Department in the News
Studying the stars with machine learning
November 12, 2018
Symmetry Magazine, by Evelyn Lamb
To keep up with an impending astronomical increase in data about our universe, astrophysicists turn to machine learning.
Kevin Schawinski had a problem.
In 2007 he was an astrophysicist at Oxford University and hard at work reviewing seven years' worth of photographs from the Sloan Digital Sky Survey - images of more than 900,000 galaxies. He spent his days looking at image after image, noting whether a galaxy looked spiral or elliptical, or logging which way it seemed to be spinning.
Technological advancements had sped up scientists' ability to collect information, but scientists were still processing information at the same rate. After working on the task full time and barely making a dent, Schawinski and colleague Chris Lintott decided there had to be a better way to do this.
There was: a citizen science project called Galaxy Zoo. Schawinski and Lintott recruited volunteers from the public to help out by classifying images online. Showing the same images to multiple volunteers allowed them to check one another's work. More than 100,000 people chipped in and condensed a task that would have taken years into just under six months.
Citizen scientists continue to contribute to image-classification tasks. But technology also continues to advance.
The Dark Energy Spectroscopic Instrument, scheduled to begin in 2019, will measure the velocities of about 30 million galaxies and quasars over five years. The Large Synoptic Survey Telescope, scheduled to begin in the early 2020s, will collect more than 30 terabytes of data each night - for a decade.
"The volume of datasets [from those surveys] will be at least an order of magnitude larger," says Camille Avestruz, a postdoctoral researcher at the University of Chicago.
To keep up, astrophysicists like Schawinski and Avestruz have recruited a new class of non-scientist scientists: machines.
Researchers are using artificial intelligence to help with a variety of tasks in astronomy and cosmology, from image analysis to telescope scheduling.
Superhuman scheduling, computerized calibration
Artificial intelligence is an umbrella term for ways in which computers can seem to reason, make decisions, learn, and perform other tasks that we associate with human intelligence. Machine learning is a subfield of artificial intelligence that uses statistical techniques and pattern recognition to train computers to make decisions, rather than programming more direct algorithms.
In 2017, a research group from Stanford University used machine learning to study images of strong gravitational lensing, a phenomenon in which an accumulation of matter in space is dense enough that it bends light waves as they travel around it.
Because many gravitational lenses can't be accounted for by luminous matter alone, a better understanding of gravitational lenses can help astronomers gain insight into dark matter.
In the past, scientists have conducted this research by comparing actual images of gravitational lenses with large numbers of computer simulations of mathematical lensing models, a process that can take weeks or even months for a single image. The Stanford team showed that machine learning algorithms can speed up this process by a factor of millions.
Schawinski, who is now an astrophysicist at ETH Zurich, uses machine learning in his current work. His group has used tools called generative adversarial networks, or GAN, to recover clean versions of images that have been degraded by random noise. They recently published a paper about using AI to generate and test new hypotheses in astrophysics and other areas of research.
Another application of machine learning in astrophysics involves solving logistical challenges such as scheduling. There are only so many hours in a night that a given high-powered telescope can be used, and it can only point in one direction at a time. "It costs millions of dollars to use a telescope for on the order of weeks," says Brian Nord, a physicist at the University of Chicago and part of Fermilab's Machine Intelligence Group, which is tasked with helping researchers in all areas of high-energy physics deploy AI in their work.
Department members: Brian Nord
Flash Center turns 20, welcomes new director
October 29, 2018
October marks the 20th anniversary of the Flash Center for Computational Science. The center is the home of FLASH, a community code with applications in fields ranging from astrophysics to engineering and biology. The center does more than develop software for simulations, however; it is also a hub for research on high-energy density physics and laboratory astrophysics.
As the center celebrates its 20th anniversary, Petros Tzeferacos, research assistant professor in the Department of Astronomy and Astrophysics at the University of Chicago, will step into the role of director of the center. After serving as director for 15 years, Don Lamb, the Robert A. Millikan Distinguished Service Professor Emeritus in the Department of Astronomy and Astrophysics, will become associate director.
The birth of a versatile framework
The center was founded in 1998 under the directorship of Robert Rosner, the William E. Wrather Distinguished Service Professor in the Department of Astronomy and Astrophysics, as part of the Accelerated Strategic Computing Initiative (ASCI) - a research program funded by the U.S. Department of Energy (DOE) to jumpstart the development of high-performance physics codes in the national labs and academia. Under Rosner's and Lamb's leadership, researchers in the center developed FLASH to study astrophysical processes that involved nuclear reactions, including supernovae explosions, x-ray bursts, and more. "Twenty years later, FLASH is being used by more than 3,000 scientists around the world to do cutting-edge research in plasma physics and astrophysics," said Tzeferacos.
In 2009, the DOE brought online the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory, the most energetic laser in the world, and made it available to academic researchers. Lamb and the Flash Center were asked by the DOE to enable the code to simulate experiments at this facility, providing researchers with an open tool to design and tune their experiments before executing them with high-energy lasers at NIF and similar labs across the globe.
According to Tzeferacos, the code's applications have continued to expand since then. "That's the beauty of FLASH," he said. "It's a versatile framework with which you can target a number of scientific applications, from fundamental plasma physics to proto-planetary disks, to galaxy formation simulations and cosmology, true to the diverse research in our department and aligned with the scientific goals of its faculty".
Turbulent dynamo and beyond
Tzeferacos was trained as a theoretical astrophysicist and developed a strong interest in applied mathematics while at the University of Turin in Italy. He joined the Flash Center in 2012 with the dream of studying the origin of cosmic magnetic fields in the lab. For decades, researchers had theorized that a process called 'turbulent dynamo' is responsible for amplifying cosmic magnetic fields to the magnitudes observed today in the universe. Recreating the necessary conditions for turbulent dynamo to work in a laboratory had been a long sought-after and challenging goal until the Flash Center and its collaborators from the University of Oxford began their concerted research effort.
Several years of simulations with FLASH and experiments at the most powerful laser facilities in the world enabled Tzeferacos and his colleagues to demonstrate the turbulent dynamo mechanism in a controlled laboratory environment for the first time. Shortly after the paper was published, Lamb lauded the accomplishment: "People have dreamed of doing this experiment with lasers for a long time, but it really took the ingenuity of this team to make this happen."
Under Tzeferacos' leadership, the center's scientists are expanding the physics and algorithms of FLASH to model plasma physics experiments with pulsed-power devices and to study fundamental astrophysical processes in magnetized plasmas. In addition, Flash Center researchers are restructuring the code to take advantage of the new supercomputing platforms that will usher in the exascale computing era. "High performance computing will always be a part of the centerís scope," Tzeferacos said.
According to Tzeferacos, the training and mentoring of young researchers is central to the Flash Centerís mission. "The center has trained scores of postdocs, graduate students, and undergraduates to make sure that the future generation of scientists is well-versed in numerical modeling and code development," he said.
Tzeferacos is excited about the future of the center. "The Flash Center and UChicago's Department of Astronomy and Astrophysics are a place where a unique synergy of plasma astrophysics and laboratory astrophysics can be realized," he said. "By modeling both astrophysical phenomena and the laboratory experiments that reveal their fundamental physical processes, we are creating a virtuous cycle that will lead to exciting discoveries and new understanding of the workings of the universe."
Department members: Donald Q. Lamb, Robert Rosner, Petros Tzeferacos
Scientific projects: Flash Center for Computational Science
Gravitational waves could soon provide measure of universe's expansion
October 23, 2018
UChicago News, by Louise Lerner
UChicago study: New LIGO readings could improve disputed measurement within 5-10 years
Twenty years ago, scientists were shocked to realize that our universe is not only expanding, but that it's expanding fasterover time.
Pinning down the exact rate of expansion, called the Hubble constant after famed astronomer and UChicago alumnus Edwin Hubble, has been surprisingly difficult. Since then scientists have used two methods to calculate the value, and they spit out distressingly different results. But last year's surprising capture of gravitational waves radiating from a neutron star collision offered a third way to calculate the Hubble constant.
That was only a single data point from one collision, but in a new paper published Oct. 17 in Nature, three University of Chicago scientists estimate that given how quickly researchers saw the first neutron star collision, they could have a very accurate measurement of the Hubble constant within five to ten years.
"The Hubble constant tells you the size and the age of the universe; it's been a holy grail since the birth of cosmology. Calculating this with gravitational waves could give us an entirely new perspective on the universe," said study author Daniel Holz, a UChicago professor in physics who co-authored the first such calculation from the 2017 discovery. "The question is: When does it become game-changing for cosmology?"
In 1929, Edwin Hubble announced that based on his observations of galaxies beyond the Milky Way, they seemed to be moving away from us - and the farther away the galaxy, the faster it was receding. This is a cornerstone of the Big Bang theory, and it kicked off a nearly century-long search for the exact rate at which this is occurring.
To calculate the rate at which the universe is expanding, scientists need two numbers. One is the distance to a faraway object; the other is how fast the object is moving away from us because of the expansion of the universe. If you can see it with a telescope, the second quantity is relatively easy to determine, because the light you see when you look at a distant star gets shifted into the red as it recedes. Astronomers have been using that trick to see how fast an object is moving for more than a century - it's like the Doppler effect, in which a siren changes pitch as an ambulance passes.
Department members: Daniel E. Holz
Department students: Maya Fishbach
Scientific projects: Laser Interferometer Gravitational-wave Observatory
Gravitational waves provide dose of reality about extra dimensions
September 18, 2018
UChicago News, by Louise Lerner
No evidence for extra spatial dimensions, UChicago scientists say
While last year's discovery of gravitational waves from colliding neutron stars was Earth-shaking, it won't add extra dimensions to our understanding of the universe -- not literal ones, at least.
University of Chicago astronomers found no evidence for extra spatial dimensions to the universe based on the gravitational wave data. Their research, published in the Journal of Cosmology and Astroparticle Physics, is one of many papers in the wake of the extraordinary announcement last year that LIGO had detected a neutron star collision.
The first-ever detection of gravitational waves in 2015, for which three physicists won the Nobel Prize last year, was the result of two black holes crashing together. Last year, scientists observed two neutron stars collide. The major difference between the two is that astronomers could see the aftermath of the neutron star collision with a conventional telescope, producing two readings that can be compared: one in gravity, and one in electromagnetic (light) waves.
"This is the very first time we've been able to detect sources simultaneously in both gravitational and light waves," said Prof. Daniel Holz. "This provides an entirely new and exciting probe, and we've been learning all sorts of interesting things about the universe."
Einstein's theory of general relativity explains the solar system very well, but as scientists learned more about the universe beyond, big holes in our understanding began to emerge. Two of these are dark matter, one of the basic ingredients of the universe; and dark energy, the mysterious force that's making the universe expand faster over time.
"This changes how a lot of people can do their astronomy."
- Astrophysicist Maya Fishbach
Scientists have proposed all kinds of theories to explain dark matter and dark energy, and "a lot of alternate theories to general relativity start with adding an extra dimension," said graduate student Maya Fishbach, a coauthor on the paper. One theory is that over long distances, gravity would "leak" into the additional dimensions. This would cause gravity to appear weaker, and could account for the inconsistencies.
The one-two punch of gravitational waves and light from the neutron star collision detected last year offered one way for Holz and Fishbach to test this theory. The gravitational waves from the collision reverberated in LIGO the morning of Aug. 17, 2017, followed by detections of gamma-rays, X-rays, radio waves, and optical and infrared light. If gravity were leaking into other dimensions along the way, then the signal they measured in the gravitational wave detectors would have been weaker than expected. But it wasn't.
It appears for now that the universe has the same familiar dimensions -- three in space and one of time -- even on scales of a hundred million light-years.
But this is just the beginning, scientists said. "There are so many theories that until now, we didn't have concrete ways to test," Fishbach said. "This changes how a lot of people can do their astronomy."
"We look forward to seeing what gravitational-wave surprises the universe might have in store for us," Holz said.
Other authors on the space-time study were Princeton's Kris Pardo and David Spergel.
Citation: "Limits on the number of space-time dimensions from GW170817." Pardo et al, Journal of Cosmology and Astroparticle Physics, July 23, 2018. doi: 10.1088/1475-7516/2018/07/048
Department members: Daniel E. Holz
Department students: Maya Fishbach
Scientific projects: Laser Interferometer Gravitational-wave Observatory
UChicago-led collaboration installed sensitive new instrument in Antarctica
September 11, 2018
University of Chicago News Office
Deep in Antarctica, at the southernmost point on our planet, sits a 33-foot telescope designed for a single purpose: to make images of the oldest light in the universe.
This light, known as the cosmic microwave background, or CMB, has journeyed across the cosmos for 14 billion years -- from the moments immediately after the Big Bang until now. Because it is brightest in the microwave part of the spectrum, the CMB is impossible to see with our eyes and requires specialized telescopes.
The South Pole Telescope, specially designed to measure the CMB, is using its third-generation camera to carry out a multi-year survey to observe the earliest instants of the universe. Since 2007, the SPT has shed light on the physics of black holes, discovered a galaxy cluster that is making stars at the highest rate ever seen, redefined our picture of when the first stars formed In the universe, provided new insights into dark energy and homed in on the masses of neutrinos. This latest upgrade improves its sensitivity by nearly an order of magnitude -- making it among the most sensitive CMB instruments ever built.
NASA Should Lead a Large Direct Imaging Mission to Study Earth-Like Exoplanets, Says New Report
September 5, 2018
The National Academies of Sciences, Engineering, and Medicine
"The NAS Exoplanet Strategy report outlines a vision for how to pursue some of the most compelling questions in modern astrophysics and planetary science, including the possible existence of life beyond our solar system."
- Prof. Jacob Bean, a member of the report committee
WASHINGTON - To answer significant questions about planetary systems, such as whether our solar system is a rare phenomenon or if life exists on planets other than Earth, NASA should lead a large direct imaging mission - an advanced space telescope - capable of studying Earth-like exoplanets orbiting stars similar to the sun, says a new congressionally mandated report by the National Academies of Sciences, Engineering, and Medicine.
The study of exoplanets - planets outside our solar system that orbit a star - has seen remarkable discoveries in the past decade. The report identifies two overarching goals in this field of science:
Based on these goals, the committee that authored the report found that our current knowledge of the range of characteristics of planets outside the solar system is substantially incomplete. A holistic approach to studying habitability in exoplanets, using both theory and observations, will ultimately be required to search for evidence of past and present life elsewhere in the universe.
While the committee recognized that developing a direct imaging capability will require large financial investments and a long time scale to see results, the effort will foster the development of the scientific community and technological capacity to understand myriad worlds. To detect a system analogous to our own Earth-sun system, the report recommends using instruments that enable direct imaging of an exoplanet by blocking the light emitted by the parent stars - such as a coronagraph or starshade.
In addition, ground-based astronomy - enabled by two U.S.-led telescopes - will also play a pivotal role in studying planet formation and potentially terrestrial worlds, the report says. The future Giant Magellan telescope (GMT) and proposed Thirty Meter Telescope (TMT) would allow profound advances in imaging and spectroscopy - absorption and emission of light - of entire planetary systems. They also could detect molecular oxygen in temperate terrestrial planets in transit around close and small stars, the report says.
The committee pointed out that the technology road map to enable the full potential of GMT and TMT in the study of exoplanets is in need of investments, and should leverage the existing network of U.S. centers and laboratories. To that end, the report recommends that the National Science Foundation invest in both telescopes and their exoplanet instrumentation to provide all-sky access to the U.S. community.
While missions like Kepler spacecraft have characterized a remarkable population of planets relatively close to their stars, our knowledge of worlds in the outer reaches of the universe is woefully lacking, the committee said. The report says WFIRST, the large space-based mission that received the highest priority in the Academies' 2010 decadal survey, will play two extremely valuable roles: first, it will permit a survey of planets farther from their stars than surveyed by Kepler and other missions. Second, it will enable a large direct imaging mission.
Although the radial velocity method - which measures the shift of the star as it orbits the center of mass of the planet system - will continue to provide essential mass and orbit information, its measurements are currently limited by variations in the surface of the star and imperfect calibration of the instruments, the report says. New instruments installed on large telescopes, substantial allocations of observing time, and collaboration between observers as well as theorists are some of the requirements for progress. To develop these methods and facilities for measuring the masses of temperate terrestrial planets orbiting sun-like stars, NASA and NSF should establish a strategic initiative in Extremely Precise Radial Velocities.
In addition, NASA should create a mechanism to systematically collect data on exoplanet atmospheres early in the James Webb Space Telescope mission. The committee also recommended building on the model of NASA's interdisciplinary collaboration initiative - Nexus for Exoplanet Science System - by supporting a cross-divisional research effort inviting proposals for interdisciplinary research.
The committee called on NASA to support a robust individual investigator program that includes grants for theoretical, laboratory, and ground-based telescopic investigations to fully realize the scientific payoff of exoplanet missions. The report also recognizes that discrimination and harassment exist in the scientific workforce and can affect the exoplanet research community, posing barriers to the participation of people from certain demographic groups. To maximize scientific potential and opportunities for excellence, institutions and organizations should take concrete steps to eliminate discrimination and harassment and to proactively recruit and retain scientists from underrepresented groups.
The study was sponsored by NASA. The National Academies of Sciences, Engineering, and Medicine are private, nonprofit institutions that provide independent, objective analysis and advice to the nation to solve complex problems and inform public policy decisions related to science, technology, and medicine. They operate under an 1863 congressional charter to the National Academy of Sciences, signed by President Lincoln.
Department members: Jacob L. Bean
Scientific projects: Giant Magellan Telescope
NASA's New Probe Sails Into the Solar Wind
August 15, 2018
The Wall Street Journal, by Angela V. Olinto
The astrophysicist Eugene Parker found only doubters 60 years ago when he proposed that a type of "wind" flows from the sun. Now NASA is sending up a spacecraft. Now NASA is sending up a spacecraft named in his honor. The Parker Solar Probe, set to launch Saturday, will fly closer to the sun than any previous mission. It will investigate why the sunís atmosphere is hotter than the sun itself, how to protect earthly electric grids from space weather, and more.
Department members: Angela V. Olinto, Eugene N. Parker
NASA Parker Solar Probe, named after UChicago scientist, begins historic mission
August 12, 2018
UChicago News, by Louise Lerner
Prof. Eugene Parker becomes first person to see launch of mission named in their honor.
At 2:31 a.m. CDT on Sunday, Aug. 12, NASA's Parker Solar Probe blasted off into the predawn darkness, on its way to explore the sun on a mission that will send it closer to our star than any previous spacecraft.
With its liftoff, University of Chicago Prof. Emeritus Eugene Parker became the first person to witness the launch of a namesake spacecraft. The Parker Space Probe is the first NASA mission named in honor of a living person.
"All I can say is wow, here we go," said Parker, who is the S. Chandrasekhar Distinguished Service Professor Emeritus in Physics at UChicago. "[Now I] really have to turn from biting my nails ... to thinking about all the interesting things which I don't know yet. We're in for some learning the next several years."
On a clear, muggy night at Cape Canaveral, with the occasional shooting star from the Perseids meteor shower streaking overhead, Parker watched from NASA's viewing terrace along with three generations of his family.
Cheers and applause erupted as the rocket climbed into the sky, and minutes later, shed its booster engines in a flare of light. After officials announced the spacecraft was safely on its way, the company hugged, shook hands and took celebratory sips of Parker Solar Pale Ale, made in honor of the occasion by local company Crystal Lake Brewing.
It was a humbling moment for Parker, who was attending his first NASA launch.
"It's a bit like the Taj Mahal. We've all seen pictures of the building and what a graceful structure it is, but ... video and paintings and so forth don't quite catch it somehow," Parker said. "It's in a different state when you're looking at the real thing."
"All I can say is wow, here we go. We're in for some learning the next several years."
- Prof. Emeritus Eugene Parker
NASA said the honor befits the magnitude of Parker's contributions to science. Parker's revolutionary scientific career began with his 1958 proposal of the "solar wind," which radically changed scientists' understandings of the solar system.
He suggested, and later NASA missions confirmed, that the sun radiates an intense stream of charged particles that travel throughout the solar system at supersonic speeds. This is visible as the halo around the sun during an eclipse, and it can affect missions in space as well as satellite communication systems on Earth.
The discovery reshaped our view of space, stars and their surroundings. It also established a new field of astrophysics, leading NASA last year to name its newest and most ambitious mission to the sun after Parker as a tribute to his work.
"We're so excited and proud that Eugene Parker's namesake mission, the Parker Solar Probe, launched this morning," said Angela Olinto, dean of the Division of the Physical Sciences at UChicago. "By first proposing the concept of the solar wind in 1958, Parker revolutionized our understanding of the solar system, and we eagerly await data from this mission that will help us continue to unravel the mysteries of our universe."
Once it leaves Earth, the Parker Solar Probe will use seven flybys of Venus to slowly reduce its orbital distance and drop closer to the sun - eventually flying into the corona, facing searing temperatures of more than a million degrees Fahrenheit.
The data it collects will provide clues to explore the still-mysterious physics behind the sun - including questions first raised by Parker's work a half-century ago, such as the nature of the mechanism that flings the solar wind off the sun.
Scientists around the world are eagerly awaiting the results, which will shed light on everything from the magnetic underpinnings of stars to the conditions that would await astronauts traveling to Mars to why the corona is so much hotter than the surface of the sun.
"The science has started on its way, and it won't stop until we know a lot more about the structure and heating of the solar corona," Parker said.
Among the company at the Kennedy Space Center was Johns Hopkins Applied Physics Laboratory scientist Nicola Fox, the Parker Solar Probe mission scientist.
"I can't think of anybody who would be more deserving of having a mission named after them than Gene Parker," she said at a news conference in Chicago held before the launch. "Physics 101 is Gene Parker's papers. It doesn't matter what you do, Gene Parker turns up somewhere in that literature."
The solar wind was only the first of Parker's discoveries; he went on to study other phenomena, such as cosmic rays and the magnetic fields of galaxies. His name is littered across the field of astrophysics: the Parker Instability, which describes magnetic fields in galaxies; the Parker equation, which describes particles moving through plasmas; the Sweet-Parker model of magnetic fields in plasmas; and the Parker limit on the flux of magnetic monopoles.
Department members: Angela V. Olinto, Eugene N. Parker
Countdown begins for launch of NASA mission named after UChicago Prof. Eugene Parker
August 6, 2018
Pioneering astrophysicist plans to become first person to watch his namesake spacecraft launch
On Aug. 11, the launch window opens for NASA's Parker Solar Probe to begin its journey to the corona of the sun, a mission that will bring a spacecraft closer to the sun than any ever before.
Watching from the Kennedy Space Center in Florida will be University of Chicago Prof. Emeritus Eugene Parker, who has dedicated his life to unraveling the sun's mysteries. He is the first living person to have a spacecraft named after him and is now preparing at the age of 91 to become the first person to see his namesake mission thunder into space.
Parker is best known for his pioneering research on the sun, which radically changed scientists' understandings of the solar system. In the 1950s, he proposed the concept of solar wind, showing that the sun radiates a constant and intense stream of charged particles that travel throughout the solar system at about one million miles per hour. This is visible as the halo around the sun during an eclipse, and it can affect missions in space as well as satellite communication systems on Earth.
"The solar probe is going to a region of space that has never been explored before. It's very exciting that we'll finally get a look," said Parker, who was on the UChicago faculty from 1955 to 1995. "One would like to have some more detailed measurements of what's going on in the solar wind. I'm sure that there will be some surprises. There always are."
Parker's theory of the solar wind challenged conventional understandings of the sun, causing scientists at the time to dismiss his work. Parker barely managed to publish the original 1958 paper that presented his theory. But he firmly defended his work, and he was ultimately proven correct in 1962 with data collected by the first successful interplanetary mission, the Mariner II space probe to Venus.
"Gene Parker's story is about challenging assumptions. He came up with a new theory and proved that theory through meticulous, scientific calculations," said Angela Olinto, dean of the Division of the Physical Sciences at UChicago. "Gene carries on a great tradition at UChicago of questioning the status quo to make discoveries and create whole new fields of science."
NASA last year named its most important mission to the sun after Parker as a tribute to his work, which established a new field of solar research. He stands as a giant among researchers who continue to push the boundaries of science, such as UChicago scientists Wendy Freedman, who was first to precisely measure the expansion rate of the universe, and Michael Turner, who coined the term dark energy.
The Parker Solar Probe is scheduled to launch during a period that opens Aug. 11. The spacecraft will use seven flybys of Venus to slowly reduce its orbital distance and drop closer to the sun. Three of the spacecraft's orbits will bring it within 3.83 million miles of the sun's surface - approximately seven times closer than any other previous mission.
The spacecraft's observations will help scientists understand why the corona is hotter than the sun's surface, how the solar wind is accelerated and what drives intense, energetic particles that can affect astronauts or interfere with onboard satellite electronics, among other questions.
"I'm sure that there will be some surprises. There always are."
- Prof. Emeritus Eugene Parker
Although Parker is the first living person to have a spacecraft named after him, he is the fifth of his peers at UChicago to have the honor, with the other four having won the recognition posthumously. They include alumnus Edwin Hubble, AB 1910, PhD 1917, with the Hubble Space Telescope; Nobel laureate Subrahmanyan Chandrasekhar, a UChicago professor who worked with Parker, with the Chandra X-ray Observatory; Enrico Fermi, a Nobel laureate and UChicago professor, with the Fermi Gamma-Ray Telescope; and Nobel laureate Arthur Holly Compton, a UChicago professor, with the Compton Gamma Ray Observatory.
Those who want to view the launch can watch on NASA's livestream. The daily launch window runs from 3:15 to 5:15 a.m. CST starting on Aug. 11.
Department members: Wendy L. Freedman, Angela V. Olinto, Eugene N. Parker, Michael S. Turner
NASA mission to sun honors pioneering UChicago physicist
August 1, 2018
Prof. Eugene Parker, who redefined how we view the sun, to witness launch of solar mission
Prof. Eugene Parker was 31 years old in 1958 when he proposed a radical idea that changed the way we think about the sun and solar system. The space between planets was not empty, he said, but filled with a "solar wind": an expanding force of particles flowing off the sun out through the farthest reaches of the solar system.
Like other scientists with outlandish theories about the sun before him, he was not believed at first.
"The first reviewer on the paper said, 'Well I would suggest that Parker go to the library and read up on the subject before he tries to write a paper about it. Because this is utter nonsense,'" Parker, the S. Chandrasekhar Distinguished Service Professor Emeritus in Physics at the University of Chicago, recalled with a laugh.
More than half a century later, in honor of his work, which opened a new field of astrophysics, Parker is the first living person to have a NASA spacecraft named after him. This month, he will travel to Cape Canaveral to watch the launch of the Parker Solar Probe, which will fly closer to the sun than any mission - all to investigate the mysterious workings of the sun and the solar wind that Parker proposed decades ago.
"Eugene Parker had a vision of the solar system that was way ahead of its time," said Prof. Angela Olinto, dean of the physical sciences at UChicago. "His work basically laid the foundation of a whole new field, and he serves as an inspiration to all of us here at the University of Chicago who are working to expand the boundaries of human knowledge."
"His work basically laid the foundation of a whole new field."
- Prof. Angela Olinto, dean of the physical sciences at UChicago
A far-out idea
Parker was a young UChicago assistant professor when he began looking into an open question in astrophysics at the time: whether there were particles coming off the sun. It seemed unlikely, since Earth's atmosphere doesn't flow out into space, and presumably the same would be true for the sun. But scientists had noticed an odd phenomenon: The tails of comets, no matter which direction they traveled, always pointed away from the sun - almost as though something was blowing them away.
Parker sat down and began to do the math. He calculated that if the sun's corona was a million degrees, there had to be a flow of particles expanding away from its surface, eventually becoming extremely fast - faster than the speed of sound. The idea was unheard of at the time, but that's what the physics was telling Parker.
"And that's the end of the story, except it isn't, because people immediately said, 'I don't believe it,'" Parker said.
He wrote a paper and submitted it to the Astrophysical Journal; the response from scientific reviewers was swift and scathing.
"You must understand how unbelievable this sounded, when he proposed it," said Fausto Cattaneo, UChicago professor of astronomy and astrophysics. "That this wind not only exists, but is traveling at supersonic speed. It is extraordinarily difficult to accelerate anything to supersonic speeds in the laboratory, and there is no means of propulsion."
Luckily, the editor of the journal at the time was eminent astrophysicist Subrahmanyan Chandrasekhar, Parker's colleague at the University of Chicago. Chandrasekhar didn't like the idea either, but the future Nobel laureate couldn't find anything wrong with the math, so he overruled the reviewers and published the paper.
And there it sat until 1962, when a NASA spacecraft to Venus called Mariner II took readings on its journey. The results were unambiguous. "There was the solar wind, blowing 24/7," Parker said.
"You must understand how unbelievable this sounded, when he proposed it."
- Prof. Fausto Cattaneo
Mission to the sun
The discovery reshaped our picture of space and the solar system. Scientists came to understand that this wind not only flows past Earth, but throughout the solar system and beyond. It also both protects and threatens us.
"The solar wind magnetically blankets the solar system, protecting life on Earth from even higher-energy particles coming from elsewhere in the galaxy," Olinto said. "But it also affects the sophisticated satellite communications we have today. So understanding the precise structure and dynamics and evolution of the solar wind is crucial for civilization as a whole."
Thus scientists have been eager for a mission to the sun since space travel first became possible. But the extreme temperatures meant they needed to wait until the development of technology that could shield the spacecraft from the intense heat and radiation of the sun. The Parker Solar Probe's heat shield, made of just under five inches of a cutting-edge carbon composite, will keep the craft's delicate instruments at a gentle 85 degrees Fahrenheit even as the corona rages at 3 million degrees Fahrenheit outside.
It will need it, because when the spacecraft launches in August, it will begin a seven-year journey to the blisteringly hot corona, visible as the halo around the sun during an eclipse. It will be by far the closest we've ever come to a star, and scientists are itching to get a look at the physics close-up.
Two of the most pressing questions for this mission, which date back to Parker's earliest work: Why is the corona so much hotter than the surface of the sun? How does the solar wind accelerate away from the sun?
A deeper understanding of these processes will help forecast space weather that affects life here on Earth, understand the conditions that astronauts in orbit above our world and journeying for long distances would face, and even provide clues about what kinds of star activity might favor habitability on distant planets.
Parker is looking forward to the data.
"You're exploring unknown territory, and you can be darn sure there are some surprises waiting for us there," he said. "Things are never quite what you thought they were."
'Gene Parker is like God'
Over his career, Parker went on to study other phenomena, such as cosmic rays and the magnetic fields of galaxies. His name is littered across the field of astrophysics: the Parker Instability, which describes magnetic fields in galaxies; the Parker equation, which describes particles moving through plasmas; the Sweet-Parker model of magnetic fields in plasmas, the Parker limit on the flux of magnetic monopoles.
"In our field, Gene Parker is like God," said Cattaneo. "Most people would have one good idea and rest on that. This guy had God knows how many. There are not many people like him."
In announcing the new name of the mission at the University last year, NASA said that given Parker's accomplishments within the field and how closely aligned this mission is with his research, the decision was made to honor him prior to launch in order to draw attention to his important contributions to heliophysics and space science.
"We're very proud to be able to carry Gene's name with us on this amazing voyage of discovery," said Nicola Fox, Parker Solar Probe project scientist, of the Johns Hopkins University Applied Physics Laboratory.
"We're very proud to be able to carry Gene's name with us on this amazing voyage of discovery."
- Nicola Fox, Parker Solar Probe project scientist
Asked for advice for those early in their careers, Parker said, "I have never made a significant proposal, but what there was a crowd who said 'Ain't so, can't possibly be.' If you do something new or innovative, expect trouble. But think critically about it because if you're wrong, you want to be the first one to know that."
Parker, who retired from the University in 1995, plans to fly to Florida with his family to watch the spacecraft launch.
"I've been delighted to be alive in this period of time because of all the wonderful things that have been happening," he said. "I'm just happy to be born at the right time."
Department members: Fausto Cattaneo, Angela V. Olinto, Eugene N. Parker
Parker Solar Probe, flying to the sun, is named after U. of C.'s own
July 31, 2018
Chicago Tribune, by Steve Johnson
From his windows up high in a Hyde Park retirement home, Eugene Parker can see, fittingly, the great mass of the Museum of Science and Industry and the distinctive rooftops of the University of Chicago.
He also can watch the sun as it rises over the lake and sets in the west, which is even more fitting because as much as any human alive, Parker is responsible for our understanding of the star that keeps us alive.
As a young U. of C. scientist in the mid-1950s, he performed some calculations and realized there must be a "solar wind" - his term - propelling material outward from the sun and affecting the entire solar system. The astronomical community scoffed at this upstart insight, and then, within a few years, early space missions proved it true.
As a 91-year-old emeritus professor in 2018, he will be at Cape Canaveral next month to watch NASA launch its Parker Solar Probe, the agency's first mission named for a living person.
NASA broke protocol, said Thomas Zurbuchen, head of the agency's Science Mission Directorate, because of "the unique impact Parker has had in the entire portfolio. We have 107 missions ongoing right now," either in operation or in planning. "Thirty-five of them are directly related to Parker's work."
"It's wonderful," said Nicola Fox, project scientist for the solar probe, which will bring science far closer to the sun than it's ever been. "He's going to stand and he's going to watch his legacy mission leave the planet and start its journey."
"He is the father of the mission. It was his paper. It was his science. It was his discovery that led to science's knowing the (sun's) corona was such an interesting place to go visit, and it's taken 60 years to be able to do this daring plunge into the sun's atmosphere."
Parker, though, isn't much for the fanfare.
In the home he and his wife share, an end table carried about the only visible sign of his fame, a stack of coaster-sized Parker Solar Probe stickers.
"A Mission to Touch the Sun," they say, the words atop an image of a spacecraft against a fiery orange inferno.
"Take one," Parker encouraged visitors late last week.
"I'm greatly honored that they would put my name on it," he said. "But I contributed nothing to the spacecraft. That's the hard work of a lot of other guys who never get much credit. They don't get interviews from the newspapers.'
But to be the first living honoree, following missions named for the likes of Kepler, Galileo, Hubble?
"I tend to shrug my shoulders at that," he said. "The fact that I'm living seems neither here nor there because I have not contributed in any way to the building of that spacecraft."
He is more focused on what the probe will learn on its seven-year mission as it loops repeatedly around Venus to propel it through the sun's atmosphere. Among the key questions being explored: How is the sun, contrary to any phenomenon on Earth, so many magnitudes hotter in its corona, the surrounding area visible in an eclipse (1.7 million degrees Fahrenheit and up), than at its surface (about 10,000 degrees), and how does it expel matter at supersonic speeds?
The sun, Parker said a couple of times, is a "very ordinary star." What we learn about it will tell us, in all likelihood, about much of the universe, although the craft's closest approach, at about 4 million miles and 2,500 degrees, won't come until 2024.
"Investigating the mechanisms of the heating are what I get most excited about," he said.
That sounds a lot like the Gene Parker she has come to know, said Fox, who will take part with the professor in a press event at the university's Gleacher Center downtown on Tuesday to draw attention to the scientist and the upcoming mission, now targeted to launch in the early morning hours of Aug. 11.
"It's like meeting Brad Pitt or somebody," she said. "He discovered the solar wind. He's kind of the father of heliophysics. ... He's this mythical person that did all this unbelievable science, and then you meet him, and he's just a lovely man."
In October Parker visited the Applied Physics Laboratory at Johns Hopkins University, where Fox is chief scientist for heliophysics and where the Parker Solar Probe was being loaded with an array of instruments that may solve some of the sun's enduring mysteries.
Again, she said, he was humble in the face of the engineering.
"I took him to meet the spacecraft that bears his name," she said.
Photographs of that event show Parker standing in the white suit required in a "clean room,' peering into the innards of the craft, and standing beside the exterior clad in the almost 5 inches of carbon that will keep it from incinerating as it flies past the sun.
Parker, she recalled, kept saying, "'You guys are the really clever ones. I just solved some equations. ... I just wrote a paper.'"
"I was like, 'Yeah, it's a pretty good paper, Gene.'"
"Dynamics of the Interplanetary Gas and Magnetic Fields" started on page 664 of volume 128 of the Astrophysical Journal, published in November, 1958.
"We consider the dynamical consequences of Biermann's suggestion that gas is often streaming outward in all directions from the sun with velocities on the order of 500-1500 km/sec," begins the paper's abstract.
They don't sound like the first words in a revolution, but those, and the words and calculations that followed, proved profound.
"People expected the space between earth and the sun to be basically a void," said Angela Olinto, a U. of C. astronomer and the university's dean of physical sciences. "Solar wind sort of connects up to the sun and all the other planets of the sun. Our local neighborhood is really quite different than the one we thought of in the 1950s."
"One of the reasons why Parker is so revered is because he was comfortable with a topic that most found arcane, difficult," said Geza Gyuk, director of astronomy at the Adler Planetarium.
The son of an engineer and grandson of a physicist, Parker, who grew up in the Buffalo and Detroit areas, was able to see the sun differently than those who had studied it before, he said, because he didn't approach it with a traditional astronomy background. Trained at Michigan State and CalTech, he was a physics guy so he tended to think in terms of systems, he said, where astronomers thought more about discrete objects.
A key to his work was the German scientist Ludwig Biermann's theory about why comet tails always point away from the sun, no matter the comet's direction of travel. Biermann suggested the sun must be emitting a stream of material, dubbed "solar corpuscular radiation," but did not explain the reason for the existence of such material.
And the British scientist Sydney Chapman had shown that the sun's corona extended beyond Earth, Parker said, but Chapman thought of the corona as a static thing.
When you add in Biermann's idea of motion, "you get an equation with one more term in it," Parker said. "And when you solve that, that makes all the difference in the world."
He looked at it as a problem similar to hydrodynamics - the flow of water - and found "thereís only one solution that fits," he said. "That's the supersonic solar winds starting slow and dense and accelerating as you go out" away from the sun.
"You put that into the mathematics, and the mathematics says, 'Well, there you are,' " he said.
Here is NASA's layperson's explanation of solar wind, from the detailed website for the Parker Solar Probe: "In the 1950s, Parker proposed a number of concepts about how stars - including our Sun - give off energy. He called this cascade of energy the solar wind, and he described an entire complex system of plasmas, magnetic fields, and energetic particles that make up this phenomenon."
But eminent astronomers in 1958 disagreed. Two of them were given the paper for peer review, and both rejected it. Their message was essentially that Parker couldn't be right because his work disagreed with conventional thinking.
"We recommend that the author go to the library and read up on the subject before he attempts to write papers about it," Parker recalled one of the scientist's critiques saying.
But there was no "real criticism," just a declaration and so Parker persisted: "I've had people say, 'Well, weren't you worried that if everybody disagreed, you might be wrong?' My reply is, 'I'm working with Newton. Newton got it right.'"
The journal's editor Subrahmanyan Chandrasekhar, a Chicago astronomer and future Nobel laureate in physics, examined the paper and told Parker he could find nothing wrong with it and he would publish it.
There was very little reaction, Parker said, but the 1962 Mariner 2 robotic voyage to Venus confirmed the solar wind's existence.
Parker continued on the faculty full time through 1995, had a major hand in guiding the university's astronomical research, colleagues said, and published important papers regularly on topics including the solar magnetic field and a theory on how the sun's corona is heated.
He won honors including the National Medal of Science, in 1989, and the Kyoto Prize for Lifetime Achievements in Basic Science, in 2003, but not the Nobel.
His theory on the lack of recognition from Sweden? "It wasn't exotic," he said of his solar wind work. "In a way I sort of feel, that just shows how much smarter you have to be to see it - because none of you guys thought of it. But anyway, I can't complain. I've gotten by all right."
Gyuk, of the Adler, thinks there may be a Nobel nomination in the offing "if his suggestions on heating mechanisms in the solar wind come to boot" as data comes in from the Parker Solar Probe.
But NASA naming the mission after him last year, no matter how much Parker might demur, represents a kind of crowning honor. It becomes doubly true when you consider how the mission will end: with the craft losing propellant and thus its ability to protect itself from the sun, vaporizing in the heat and joining the solar wind.
Department members: Angela V. Olinto, Eugene N. Parker
NASA Prepares to Launch Parker Solar Probe, a Mission to Touch the Sun
July 20, 2018
NASA, by Sarah Frazier
Early on an August morning, the sky near Cape Canaveral, Florida, will light up with the launch of Parker Solar Probe. No earlier than Aug. 6, 2018, a United Launch Alliance Delta IV Heavy will thunder to space carrying the car-sized spacecraft, which will study the Sun closer than any human-made object ever has.
On July 20, 2018, Nicky Fox, Parker Solar Probe's project scientist at the Johns Hopkins University Applied Physics Lab in Laurel, Maryland, and Alex Young, associate director for science in the Heliophysics Science Division at NASA's Goddard Space Flight Center in Greenbelt, Maryland, introduced Parker Solar Probe's science goals and the technology behind them at a televised press conference from NASA's Kennedy Space Center in Cape Canaveral, Florida.
"We've been studying the Sun for decades, and now we're finally going to go where the action is," said Young.
Our Sun is far more complex than meets the eye. Rather than the steady, unchanging disk it seems to human eyes, the Sun is a dynamic and magnetically active star. The Sun's atmosphere constantly sends magnetized material outward, enveloping our solar system far beyond the orbit of Pluto and influencing every world along the way. Coils of magnetic energy can burst out with light and particle radiation that travel through space and create temporary disruptions in our atmosphere, sometimes garbling radio and communications signals near Earth. The influence of solar activity on Earth and other worlds are collectively known as space weather, and the key to understanding its origins lies in understanding the Sun itself.
"The Sun's energy is always flowing past our world," said Fox. "And even though the solar wind is invisible, we can see it encircling the poles as the aurora, which are beautiful - but reveal the enormous amount of energy and particles that cascade into our atmosphere. We don't have a strong understanding of the mechanisms that drive that wind toward us, and that's what we're heading out to discover."
That's where Parker Solar Probe comes in. The spacecraft carries a lineup of instruments to study the Sun both remotely and in situ, or directly. Together, the data from these state-of-the-art instruments should help scientists answer three foundational questions about our star.
One of those questions is the mystery of the acceleration of the solar wind, the Sun's constant outflow of material. Though we largely grasp the solar wind's origins on the Sun, we know there is a point - as-yet unobserved - where the solar wind is accelerated to supersonic speeds. Data shows these changes happen in the corona, a region of the Sun's atmosphere that Parker Solar Probe will fly directly through, and scientists plan to use Parker Solar Probe's remote and in situ measurements to shed light on how this happens.
Second, scientists hope to learn the secret of the corona's enormously high temperatures. The visible surface of the Sun is about 10,000 F - but, for reasons we don't fully understand, the corona is hundreds of times hotter, spiking up to several million degrees F. This is counterintuitive, as the Sun's energy is produced at its core.
"It's a bit like if you walked away from a campfire and suddenly got much hotter," said Fox.
Finally, Parker Solar Probe's instruments should reveal the mechanisms at work behind the acceleration of solar energetic particles, which can reach speeds more than half as fast as the speed of light as they rocket away from the Sun. Such particles can interfere with satellite electronics, especially for satellites outside of Earth's magnetic field.
To answer these questions, Parker Solar Probe uses four suites of instruments.
The FIELDS suite, led by the University of California, Berkeley, measures the electric and magnetic fields around the spacecraft. FIELDS captures waves and turbulence in the inner heliosphere with high time resolution to understand the fields associated with waves, shocks and magnetic reconnection, a process by which magnetic field lines explosively realign.
The WISPR instrument, short for Wide-Field Imager for Parker Solar Probe, is the only imaging instrument aboard the spacecraft. WISPR takes images from of structures like coronal mass ejections, or CMEs, jets and other ejecta from the Sun to help link what's happening in the large-scale coronal structure to the detailed physical measurements being captured directly in the near-Sun environment. WISPR is led by the Naval Research Laboratory in Washington, D.C.
Another suite, called SWEAP (short for Solar Wind Electrons Alphas and Protons Investigation), uses two complementary instruments to gather data. The SWEAP suite of instruments counts the most abundant particles in the solar wind - electrons, protons and helium ions - and measures such properties as velocity, density, and temperature to improve our understanding of the solar wind and coronal plasma. SWEAP is led by the University of Michigan, the University of California, Berkeley, and the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts.
Finally, the ISʘIS suite - short for Integrated Science Investigation of the Sun, and including ʘ, the symbol for the Sun, in its acronym - measures particles across a wide range of energies. By measuring electrons, protons and ions, ISʘIS will understand the particles' lifecycles - where they came from, how they became accelerated and how they move out from the Sun through interplanetary space. ISʘIS is led by Princeton University in New Jersey.
Parker Solar Probe is a mission some sixty years in the making. With the dawn of the Space Age, humanity was introduced to the full dimension of the Sun's powerful influence over the solar system. In 1958, physicist Eugene Parker published a groundbreaking scientific paper theorizing the existence of the solar wind. The mission is now named after him, and it's the first NASA mission to be named after a living person.
Only in the past few decades has technology come far enough to make Parker Solar Probe a reality. Key to the spacecraft's daring journey are three main breakthroughs: The cutting-edge heat shield, the solar array cooling system, and the advanced fault management system.
"The Thermal Protection System (the heat shield) is one of the spacecraft's mission-enabling technologies," said Andy Driesman, Parker Solar Probe project manager at the Johns Hopkins Applied Physics Lab. "It allows the spacecraft to operate at about room temperature."
Other critical innovations are the solar array cooling system and on-board fault management systems. The solar array cooling system allows the solar arrays to produce power under the intense thermal load from the Sun and the fault management system protects the spacecraft during the long periods of time when the spacecraft can't communicate with the Earth.
Using data from seven Sun sensors placed all around the edges of the shadow cast by the heat shield, Parker Solar Probe's fault management system protects the spacecraft during the long periods of time when it can't communicate with Earth. If it detects a problem, Parker Solar Probe will self-correct its course and pointing to ensure that its scientific instruments remain cool and functioning during the long periods when the spacecraft is out of contact with Earth.
Parker Solar Probe's heat shield - called the thermal protection system, or TPS - is a sandwich of carbon-carbon composite surrounding nearly four and half inches of carbon foam, which is about 97% air. Though it's nearly eight feet in diameter, the TPS adds only about 160 pounds to Parker Solar Probe's mass because of its lightweight materials.
Though the Delta IV Heavy is one of the world's most powerful rockets, Parker Solar Probe is relatively small, about the size of a small car. But what Parker Solar Probe needs is energy - getting to the Sun takes a lot of energy at launch to achieve its orbit around the Sun. That's because any object launched from Earth starts out traveling around the Sun at the same speed as Earth - about 18.5 miles per second - so an object has to travel incredibly quickly to counteract that momentum, change direction, and go near the Sun.
The timing of Parker Solar Probe's launch - between about 4 and 6 a.m. EDT, and within a period lasting about two weeks - was very precisely chosen to send Parker Solar Probe toward its first, vital target for achieving such an orbit: Venus.
"The launch energy to reach the Sun is 55 times that required to get to Mars, and two times that needed to get to Pluto," said Yanping Guo from the Johns Hopkins Applied Physics Laboratory, who designed the mission trajectory. "During summer, Earth and the other planets in our solar system are in the most favorable alignment to allow us to get close to the Sun."
The spacecraft will perform a gravity assist to shed some of its speed into Venus' well of orbital energy, drawing Parker Solar Probe into an orbit that - already, on its first pass - carries it closer to the solar surface than any spacecraft has ever gone, well within the corona. Parker Solar Probe will perform similar maneuvers six more times throughout its seven-year mission, assisting the spacecraft to final sequence of orbits that pass just over 3.8 million miles from the photosphere.
"By studying our star, we can learn not only more about the Sun,' said Thomas Zurbuchen, the associate administrator for the Science Mission Directorate at NASA HQ. "We can also learn more about all the other stars throughout the galaxy, the universe and even life's beginnings."
Parker Solar Probe is part of NASA's Living with a Star Program, or LWS, to explore aspects of the Sun-Earth system that directly affect life and society. LWS is managed by NASA's Goddard Space Flight Center in Greenbelt, Maryland, for the Heliophysics Division of NASA's Science Mission Directorate in Washington. Johns Hopkins APL manages the Parker Solar Probe mission for NASA. APL designed and built the spacecraft and will also operate it.
Department members: Eugene N. Parker
NASA's Webb Space Telescope to Inspect Atmospheres of Gas Giant Exoplanets
July 11, 2018
NASA, by Christine Pulliam
In April 2018, NASA launched the Transiting Exoplanet Survey Satellite (TESS). Its main goal is to locate Earth-sized planets and larger "super-Earths" orbiting nearby stars for further study. One of the most powerful tools that will examine the atmospheres of some planets that TESS discovers will be NASA's James Webb Space Telescope. Since observing small exoplanets with thin atmospheres like Earth will be challenging for Webb, astronomers will target easier, gas giant exoplanets first.
Some of Webb's first observations of gas giant exoplanets will be conducted through the Director's Discretionary Early Release Science program. The transiting exoplanet project team at Webb's science operations center is planning to conduct three different types of observations that will provide both new scientific knowledge and a better understanding of the performance of Webb's science instruments.
"We have two main goals. The first is to get transiting exoplanet datasets from Webb to the astronomical community as soon as possible. The second is to do some great science so that astronomers and the public can see how powerful this observatory is," said Jacob Bean of the University of Chicago, a co-principal investigator on the transiting exoplanet project.
"Our team's goal is to provide critical knowledge and insights to the astronomical community that will help to catalyze exoplanet research and make the best use of Webb in the limited time we have available," added Natalie Batalha of NASA Ames Research Center, the project's principal investigator.
Transit - An atmospheric spectrum
When a planet crosses in front of, or transits, its host star, the star's light is filtered through the planet's atmosphere. Molecules within the atmosphere absorb certain wavelengths, or colors, of light. By splitting the star's light into a rainbow spectrum, astronomers can detect those sections of missing light and determine what molecules are in the planet's atmosphere.
For these observations, the project team selected WASP-79b, a Jupiter-sized planet located about 780 light-years from Earth. The team expects to detect and measure the abundances of water, carbon monoxide, and carbon dioxide in WASP-79b. Webb also might detect new molecules not yet seen in exoplanet atmospheres.
Phase curve - A weather map
Planets that orbit very close to their stars tend to become tidally locked. One side of the planet permanently faces the star while the other side faces away, just as one side of the Moon always faces the Earth. When the planet is in front of the star, we see its cooler backside. But as it orbits the star, more and more of the hot day-side comes into view. By observing an entire orbit, astronomers can observe those variations (called a phase curve) and use the data to map the planet's temperature, clouds, and chemistry as a function of longitude.
The team will observe a phase curve of the "hot Jupiter" known as WASP-43b, which orbits its star in less than 20 hours. By looking at different wavelengths of light, they can sample the atmosphere to different depths and obtain a more complete picture of its structure. "We have already seen dramatic and unexpected variations for this planet with Hubble and Spitzer. With Webb we will reveal these variations in significantly greater detail to understand the physical processes that are responsible," said Bean.
Eclipse - A planet's glow
The greatest challenge when observing an exoplanet is that the star's light is much brighter, swamping the faint light of the planet. To get around this problem, one method is to observe a transiting planet when it disappears behind the star, not when it crosses in front of the star. By comparing the two measurements, one taken when both star and planet are visible, and the other when only the star is in view, astronomers can calculate how much light is coming from the planet alone.
This technique works best for very hot planets that glow brightly in infrared light. The team plans to study WASP-18b, a planet that is baked to a temperature of almost 4,800 degrees Fahrenheit (2,900 K). Among other questions, they hope to determine whether the planet's stratosphere exists due to the presence of titanium oxide, vanadium oxide, or some other molecule.
Ultimately, astronomers want to use Webb to study potentially habitable planets. In particular, Webb will target planets orbiting red dwarf stars since those stars are smaller and dimmer, making it easier to tease out the signal from an orbiting planet. Red dwarfs are also the most common stars in our galaxy.
"TESS should locate more than a dozen planets orbiting in the habitable zones of red dwarfs, a few of which might actually be habitable. We want to learn whether those planets have atmospheres and Webb will be the one to tell us," said Kevin Stevenson of the Space Telescope Science Institute, a co-principal investigator on the project. "The results will go a long way towards answering the question of whether conditions favorable to life are common in our galaxy."
The James Webb Space Telescope will be the world's premier space science observatory. Webb will solve mysteries of our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international project led by NASA with its partners, the European Space Agency (ESA) and the Canadian Space Agency (CSA).
Department members: Jacob L. Bean
Doyal "Al" Harper has received a Norman Maclean Faculty Award
June 7, 2018
UChicago News, by Ryan Goodwin
The Norman Maclean Faculty Award recognizes emeritus or senior faculty for extraordinary contributions to teaching and to the student experience of life within the University community. This year's recipient is Doyal "Al" Harper, professor in the Department of Astronomy and Astrophysics and the College.
Prof. Doyal "Al" Harper has mentored and supported countless students in the Department of Astronomy and Astrophysics and in the College and has been an enthusiastic research adviser to both undergraduate and graduate students at UChicago. Students have benefited in particular from the wide range of research opportunities he provides--they are able to do hands-on work in the laboratory, design and build instrumentation, carry out observational programs at ground-based and airborne observatories, and develop and employ computational tools for data analysis.
Harper's research addresses problems in the formation of galaxies, stars and planetary systems; the physics of the interstellar medium; and the properties of interstellar dust. His experimental research group constructs and operates infrared instrumentation and pioneered airborne infrared astronomy and astrophysical observations from the South Pole.
Department members: Doyal ''Al'' Harper
Angela Olinto named dean of Physical Sciences Division
June 7, 2018
Angela V. Olinto, the Albert A. Michelson Distinguished Service Professor in the Department of Astronomy and Astrophysics, has been appointed dean of the Division of the Physical Sciences at the University of Chicago.
Olinto is a leading scholar in astroparticle physics and cosmology, focusing on understanding the origin of high-energy cosmic rays, gamma rays and neutrinos. Her appointment as dean is effective July 1.
"Angela brings depth of University experience and scholarly expertise to this leadership role, making her an excellent choice as dean," wrote President Robert J. Zimmer and Provost Daniel Diermeier in announcing her appointment.
Olinto's research includes important contributions to the physics of quark stars, inflationary theory and cosmic magnetic fields. She currently leads NASA sub-orbital and space missions to discover the origins of high-energy cosmic rays and neutrinos. This includes a NASA-funded balloon mission planned for 2022 that will use an ultra-sensitive telescope to detect cosmic rays and neutrinos coming from deep space.
"I am thrilled and humbled to be appointed to lead this historic and dynamic division, home to visionary scholars who constantly redefine the boundaries of the physical and mathematical sciences. I look forward to collaborating with faculty, students and staff to advance the important work of the division," Olinto said.
Olinto joined the UChicago faculty in 1996 and served as chair of the Department of Astronomy and Astrophysics from 2003 to 2006 and from 2012 to 2017. She is the leader of the POEMMA and EUSO space missions and a member of the Pierre Auger Observatory, which are international projects designed to discover the origin of high-energy cosmic rays. She is a fellow of the American Physical Society, was a trustee of the Aspen Center for Physics, and serves on advisory committees for the National Academy of Sciences, U.S. Department of Energy, the National Science Foundation and NASA.
Olinto's awards and honors include the Chaire d'Excellence Award of the French Agence Nationale de la Recherche in 2006, the University's Llewellyn John and Harriet Manchester Quantrell Award for Excellence in Undergraduate Teaching in 2011, and the Faculty Award for Excellence in Graduate Teaching and Mentoring in 2015. Olinto received her undergraduate degree from Pontificia Universidade Catolica in Rio de Janeiro, Brazil and her doctoral degree from the Massachusetts Institute of Technology.
Olinto succeeds Edward "Rocky" Kolb, the Arthur Holly Compton Distinguished Service Professor of Astronomy & Astrophysics, whose work over the last five years enhanced the division's historic strengths as a leading center of scientific discovery. Kolb will return to his full-time work on the faculty next month.
The selection of the new dean by Zimmer and Diermeier was informed by the recommendations of an elected faculty committee chaired by Stuart A. Kurtz, professor in the Department of Computer Science.
Department members: Edward ''Rocky'' W. Kolb, Angela V. Olinto
Scientific projects: Extreme Universe Space Observatory at the Japanese Module, Extreme Universe Space Observatory on a Super Pressure Balloon, Pierre Auger Observatory
NASA Spacecraft Discovers New Magnetic Process in Turbulent Space
May 24, 2018
In a new discovery reported in the journal Nature, scientists working with NASA's Magnetospheric Multiscale spacecraft -- MMS -- have uncovered a new type of magnetic event in our near-Earth environment by using an innovative technique to squeeze extra information out of the data. Astronomy & Astrophysics postdoctoral scholar Colby Haggerty was part of the team of scientists who made this exciting discovery.
Department members: Colby Haggerty
Big Brains podcast explores how world's largest telescope might glimpse universe's birth
May 15, 2018
UChicago News, by Andrew Bauld
Cosmologist Wendy Freedman on how new technology could lead to major discoveries
Prof. Wendy Freedman spent much of her career measuring the age of the universe. Now she's working on a project that may very well give scientists a chance to glimpse into its birth.
Freedman, the John & Marion Sullivan University Professor of Astronomy & Astrophysics, works in the field of observational cosmology, measuring the expansion rate of the universe. In 2001, she and a team of scientists found that the universe is around 13.7 billion years old -- far more precise than the previous estimate in the 10- to 20-billion-year-old range.
Freedman was the founding leader from 2003 until 2015 of an international consortium of researchers and universities (including UChicago) to build the world's largest telescope high in the mountains of Chile. The Giant Magellan Telescope will be as tall as the Statue of Liberty when complete, and ten times more powerful than the Hubble Space Telescope -- with the ability to look back at the dawn of the cosmos.
"In our field, the new developments have come with new technology," Freedman said. "Without exception, from the time that Galileo first turned a telescope to the sky in 1609, every time we've built a new capability we've made new discoveries, which is why we're so excited about this."
The telescope, 80 feet in diameter and weighing more than 20 tons, will be the first of its kind to see fine details like a planet's atmosphere, which could one day help discover life on other planets. The telescope is expected to be operational starting in 2024.
"If we really were able to show that there's life on a planet outside of our own solar system, that will be one of the discoveries that will not only be exciting for astronomers but will change human kind's perspective on our place in the universe," Freedman said.
On this episode of Big Brains, Freedman discusses her research on measuring the age of the universe, her leadership of the Giant Magellan Telescope and the search for life outside our solar system.
Department members: Wendy L. Freedman
Scientific projects: Giant Magellan Telescope
ALMA follow up of SPT sources discovers massive conglomerations of Star Forming Galaxies in early Universe
May 1, 2018
National Radio Astronomy Observatory
Peering deep into space - an astounding 90 percent of the way across the observable universe - astronomers have witnessed the beginnings of a gargantuan cosmic pileup, the impending collision of 14 young, starbursting galaxies. This ancient megamerger is destined to evolve into one of the most massive structures in the known universe: a cluster of galaxies, gravitationally bound by dark matter and swimming in a sea of hot, ionized gas.
Cosmologists Can't Agree on the Hubble Constant
April 23, 2018
American Physical Society, by David Ehrenstein
The discrepancy in measures of the Hubble constant, which quantifies the expansion of the Universe, has only grown in recent years.
The Hubble constant H0 tells us the speed at which galaxies are receding from us as the Universe expands. Over the past five years, cosmologists have recognized that there is a discrepancy between different measurements of this fundamental parameter. Three speakers in a session at the April Meeting of the American Physical Society in Columbus, Ohio, discussed the status of this "crisis in cosmology." The field has now accepted that the problem is real, and some researchers are optimistic that it could lead to important discoveries.
The problem began in 2013, when the first results were reported from the Planck satellite, which had measured the cosmic microwave background (CMB). The Planck team's value for H0 was 67.±1.2 kilometers per second per megaparsec (km/s/Mpc), lower than previous measurements, which had been between 70 and 75 km/s/Mpc. The result also had error bars small enough that even this slight difference was a potential problem. Planck's 2015 result was not very different, though it came with even smaller error bars.
Prior to the Planck announcement, the Supernova H0 for the Equation of State (SH0ES) Collaboration, led by Adam Riess of Johns Hopkins University in Baltimore, had already set out to make a measurement ofH0 in our cosmic neighborhood with higher precision than previous efforts. The researchers focused on re-calibrating three of the standard distance-measuring techniques from scratch - the motion of stars due to Earth's orbit (parallax), pulsating stars known as Cepheid variables, and Type Ia supernovae, said team member David Jones of the University of California at Santa Cruz. Based on their improved distance measures, SH0ES reported an H0 value of 73.2 ± 1.7 km/s/Mpc in 2016. This result differed from Planck's by more than 3 standard deviations, a highly statistically significant difference that could not easily be explained.
Re-analyses of the SH0ES results confirmed the 2016 finding, as did additional measurements of H0 in the local Universe. But an independent H0 determination in 2016 based on so-called baryon acoustic oscillations - the sloshing of matter in the early Universe that produced the characteristic CMB patterns - lined up with the Planck result.
Stephen Feeney of the Flatiron Institute in New York said that despite quite a bit of attention to the issue, no one has found any problems with the measurements that could have a large enough effect to close the gap. Cosmologists have also been discussing whether the standard cosmological model, known as ΛCDM, may require modification. This theory is used for the CMB-based determinations of H0. But the proposed adjustments to ΛCDM all introduce at least some conflicts with other types of data. Feeney estimates that the odds are 60:1 that all of the data could be explained by statistical flukes and ΛCDM alone.
Last year, the Planck team performed a more detailed analysis of their data and found that the CMB fluctuations on the smallest angular scales had the largest effect on lowering H0. Describing these results, Bradford Benson of Fermilab said that when the team used only their data from larger angular scales (above about 0.2o), they derived an H0 value consistent with the SH0ES result.
According to Benson, the smaller angular scales provide a more sensitive test of a particular parameter in ΛCDM than larger scales. The parameter is the density of neutrinos in the Universe, which should be proportional to the number of neutrino species (there are three in the standard model of particle physics). Increasing the number of neutrino types is one of the few ways to reasonably tweak ΛCDM and increase Planck's H0 enough to close the gap with local measurements. However, this solution would also require more massive neutrinos to avoid disagreements with other cosmological data sets, said Benson. And of course, there isn't much evidence for a fourth neutrino type.
Jones, Feeney, and Benson agreed that the discrepancy isn't going away and that more data are essential to explain it. The expected future trove of gravitational waves from binary neutron star mergers, for example, will provide independent estimates for H0. (Last year's event led to a value somewhere between those of Planck and SH0ES but with much larger error bars.) In addition, the South Pole Telescope and the Atacama Cosmology Telescope have upgraded equipment that will soon provide better CMB maps, and the Gaia satellite will provide a new level of precision parallax measurements.
Benson thinks there's a good chance that a "benign" explanation will solve the problem. However, in a different session, Riess pointed out that problems with the value of H0 have led to great discoveries in the past, including the existence of dark energy.
Department members: Bradford A. Benson
Scientific projects: South Pole Telescope
2018: Norman Maclean Faculty Award - Doyal "Al" Harper
April 12, 2018
University of Chicago, Alumni Association
Al Harper is a professor in the Department of Astronomy and Astrophysics and director of Yerkes Observatory in Williams Bay, Wisconsin. His research addresses problems in the formation of galaxies, stars, and planetary systems; the physics of the interstellar medium; and the properties of interstellar dust. His experimental research group constructs and operates infrared instrumentation and pioneered airborne infrared astronomy and astrophysical observations from the South Pole.
In addition to his scientific research contributions, Professor Harper has mentored and supported countless students and has been an enthusiastic research adviser to both undergraduate and graduate students at UChicago. Students have benefited in particular from the wide range of research opportunities he provides--they are able to do hands-on work in the laboratory, design and build instrumentation, carry out observational programs at ground-based and airborne observatories, and develop and employ computational tools for data analysis.
Professor Harper's commitment to the students at the University of Chicago has been an incredible gift to those he has taught and mentored. One current project is the renovation and modernization of a telescope at Yerkes Observatory so that it can be used for teaching and student projects at the undergraduate level. This is just one example of his dedication to the students in the University community. Professor Harper embraces teaching and one-on-one guidance as central to his career, and all his students can attest to his generosity and leadership capabilities.
Department members: Doyal ''Al'' Harper
Lab experiments mimic the origin and growth of astrophysical magnetic fields
April 3, 2018
Physics Today, by Rachel Berkowitz
A turbulent, laser-generated plasma can amplify magnetic fields to cosmic scales.
Magnetic fields permeate the space between objects throughout the universe, from galaxy clusters to protogalaxies to nebulae. It's not difficult to explain how those fields might be initiated: Weak fields originate in astrophysical plasmas through various mechanisms - for example, temperature or density gradients in the plasma that alter electron trajectories.
But it remains challenging to demonstrate how seed fields of 10−21 gauss in intergalactic space grow to their measured astronomical values of several microgauss. Theory suggests that turbulent motion in an astrophysical plasma amplifies tiny magnetic fields by converting kinetic energy into magnetic energy. Such a self-sustaining energy conversion mechanism is called a dynamo.
Dynamos are often distinguished between large scale and small scale. The familiar large-scale geodynamo relies on Earth's symmetry-breaking rotation to generate a magnetic field that grows at scales larger than those of the liquid-core motion. But in a small-scale dynamo, the magnetic field grows below the length scales of fluid motion. There, turbulence operates first at the smallest length scales, where it rapidly amplifies the fields. The mechanism works even in isotropic conditions.
Now Gianluca Gregori (Oxford University), Petros Tzeferacos (University of Chicago), and colleagues have measured the amplification of a magnetic field in a turbulent laboratory plasma and provided the first physical demonstration of a dynamo resulting from turbulent motion.1 The study shows that the turbulent dynamo could be a viable mechanism for magnetic field amplification in the lab and in astrophysical settings.
Galaxies far, far away
To sustain a dynamo, a fluid needs to be electrically conductive, and its motion cannot be too symmetric. Dynamo conditions also require that the magnetic field lines stay in the plasma, rather than diffusing away. Those conditions are easily satisfied by the turbulent, high-temperature, high-velocity plasma that fills intergalactic space.
Even though conditions favorable for dynamos are common in astrophysical settings, the strong turbulence is extremely difficult to replicate in the lab. (See the article by Daniel Lathrop and Cary Forest, Physics Today, July 2011, page 40.) Astronomical x-ray observations provide information about the temperature, density, and composition of hot plasmas in the universe. But observations cannot convey the geometry and topology of the magnetic field lines, both of which strongly affect basic plasma processes such as thermal conduction. Most knowledge of how astrophysical plasmas behave is based on numerical simulations and modeling.2
Joseph Larmor first invoked the dynamo mechanism a hundred years ago to explain solar magnetic fields,3 and theoretical predictions of how the turbulent dynamo should operate go back more than half a century. In 2001 Agris Gailitis and colleagues achieved the first laboratory amplification of a self-exciting magnetic field in a turbulent swirling flow of liquid sodium.4 In 2012 Gregori generated shock waves in a laboratory plasma with a laser and showed that asymmetric shocks, like those occurring in supernovae remnants and gamma-ray bursts, produced seed magnetic fields.5 But the plasma did not reach high enough temperature and velocity to trigger and sustain the dynamo effect. The advent of high-power lasers has now opened a new field of research in which astrophysical environments can be studied in the laboratory.
Galaxy in a lab
At the Omega Laser Facility at the University of Rochester, Tzeferacos and his colleagues irradiated two fixed targets of penny-sized pieces of chlorine-doped polystyrene foil with a series of progressively stronger UV laser pulses to deliver a total of 5 kJ to each target. The foils faced each other 8 mm apart. The laser energy quickly stripped and ionized each foil's atoms and generated two hot plasma jets directed toward each other. Along the way the jets each passed through a grid of holes. The grids were offset from each other and created interpenetrating fingers of plasma that sheared when they collided and generated a strongly turbulent region. Colliding plasma jets offer a laboratory representation of merging galaxy clusters.
"We've tried similar experiments at smaller-scale facilities, but generating plasma conditions where a dynamo can operate was impossible. We needed the power and diagnostics of Omega," says Tzeferacos. The Omega laser experiments were based on earlier efforts by Tzeferacos, Gregori, and colleagues that used the IR Vulcan laser at the UK's Rutherford Appleton Laboratory but that did not have sufficient power to achieve dynamo conditions. (See Physics Today, September 2015, page 16.)
Images taken by an x-ray framing camera showed that the experiments reached the turbulent regime. Inhomogeneities developed in a region more than 1 mm across after the plasma flows collided (see figure 2a). The intensity fluctuations are directly related to electron density fluctuations, which in turn indicate the plasma turbulence. Results from numerical simulations, seen in figure 2b, verify that x-ray images capture the electron density fluctuations expected in a turbulent plasma.
"The big advance was getting the laboratory plasmas to high enough temperature and velocity," says Christopher Reynolds (University of Cambridge). "We have good simulations, but at the end of the day, lab work is real gas doing real things."
Tzeferacos and colleagues used numerical simulations to develop two methods for measuring the magnetic field produced by the plasma. Simulations were necessary to determine when to run the diagnostic tools since the experiments lasted tens of nanoseconds, but the strongly amplified magnetic fields persisted for only a fraction of that time.
In one method, the researchers measured the polarization of light passing through the plasma. They based their approach on a technique astronomers use to measure the magnetic fields of distant objects. In the other method, they imaged protons fired through the plasma. Protons are focused into concentrated regions by a magnetic field that bends the protons' trajectories. By analyzing the concentration of protons, the researchers could reconstruct the magnetic field at the moment the protons were fired through the plasma.
Both methods determined the magnetic field in the turbulent region at several times during the experiment and found that in less than 10 ns, the field amplified by a factor of 25-30. On galactic spatial and temporal scales, the same amplification mechanism could grow a tiny seed field to the observed values.
The initially weak magnetic fields in turbulent dynamo theory evolve according to Maxwell's equations. When the magnetic field becomes strong enough to deflect the moving plasma, the magnetic energy grows linearly until the plasma motion can no longer amplify the magnetic field. The ratio between magnetic and kinetic energy saturates at a value that depends on the individual fluid properties.
From the lab measurements, the team determined that the magnetic field energy of the plasma saturated at about 4% of its kinetic energy. "It's reasonable that the mean magnetic energy is quantitatively smaller than the kinetic energy," says Tzeferacos. Larger and denser plasmas would give the same result, and the measured 4% value is consistent with models in the literature.
Numerical simulations supported the case that the precollision plasmas became primed with tiny seed magnetic fields as a result of density and temperature gradients produced by the laser.6 Simulations also showed that the fields grew exponentially, but the experiments did not temporally resolve the magnetic field growth rate. Follow-up experiments will address the rate at which the magnetic field grows and other, more detailed questions.
From lab to universe
"The fact that the dynamo effect is seen in an experiment validates simulations and provides very strong evidence that this is indeed what happens in the universe at large," Gregori says. The equations that describe fluids are scale independent - waves in a water glass have the same properties as waves in the ocean.
For magnetic fields, the condition for scale invariance is that the magnetized fluid remains a good conductor. Mathematically, the condition means that a dimensionless parameter called the magnetic Reynolds number Rm is above a critical threshold value of 200. The higher the Rm, the more closely the magnetic field lines move with the plasma. The experiments achieved an Rm of 600, consistent with modeled intergalactic plasmas.
Reynolds observes that "lab work has often not had the prominence it deserves in astrophysics, because it's difficult to get gases to have meaningful properties. Experiments like this are important for providing fundamental verification of an important theory."
Atoms in a laboratory plasma frequently collide with each other. That tends to homogenize the plasma, making laboratory plasmas simple to analyze. Unfortunately, the same homogenization does not occur in many less dense astrophysical plasmas, which are harder to understand. However, laboratory plasmas are beginning to approach the collision rate of their astrophysical brethren.
The laboratory platform offers a new opportunity to test theories about magnetic turbulent plasmas in situations relevant to astrophysics, and to analyze how charged particle acceleration develops in a plasma. Future experiments could provide insight into how quickly the magnetic field increases in strength, how strong it can get, and how it alters the turbulence that amplified it.
Department members: Petros Tzeferacos
Scientific projects: Flash Center for Computational Science
2018 APS Medal for Exceptional Achievement in Research
March 20, 2018
The 2018 APS Medal for Exceptional Achievement in Research was awarded on February 1 to Eugene Parker, professor emeritus at the University of Chicago, for his "many fundamental contributions to space physics, plasma physics, solar physics, and astrophysics during the past 60 plus years." (Top Left) The medal was presented to Parker by 2018 APS President Roger Falcone along with APS CEO Kate Kirby. (Top Right) Family members and colleagues joined in the celebration: from left to right, Eric Parker, Susan Kane-Parker, Niesje Parker, Eugene Parker (seated); Michael Turner, Rocky Kolb, and Young-Kee Kim (University of Chicago), and Timothy Gay (University of Nebraska-Lincoln, APS Speaker of the Council, and University of Chicago Ph.D. graduate). APS is accepting nominations for the 2019 APS Medal now through May 1.
Department members: Edward ''Rocky'' W. Kolb, Eugene N. Parker, Michael S. Turner
Stephen Hawking: A physicist's appreciation
March 16, 2018
Bulletin of the Atomic Scientists, by Daniel Holz
Stephen Hawking was a singular individual, revered both by his fellow scientists and by the public. His books were bestsellers, his public lectures were always standing-room-only, and as a sign of his broad appeal, he appeared in Star Trek, The Simpsons, and The Big Bang Theory. He became a household name. Hawking was passionate about his science, but also passionate about sharing his unique insights with the world.
His scientific legacy is assured. I believe his discovery that black holes have a temperature is one of the most beautiful and profound accomplishments of humankind, bar none. Hawking presented his results in a paper titled "Particle creation by black holes." This relatively innocuous title hides a revolution in physics. The paper is staggeringly perfect, combining physical insight with technical mastery, and is thrilling to read even 40 years later and will remain so for the foreseeable future.
Black holes are the most extreme objects in the universe, regions where the gravity is so strong that nothing can escape. Hawking showed that when you add quantum mechanics, the uncertainty principle results in particles appearing to leak out of the black holes, and thus black holes have a temperature. Black holes aren't truly black! This is a beautiful result, vividly demonstrating the unity of physics, while hinting at some underlying, fundamental processes that we have yet to understand. Because black holes radiate particles, they must lose mass, in a process known as black hole evaporation. As the black holes radiate they get smaller, and thus hotter, meaning that they radiate energy faster, and thus get even smaller and even hotter, and so on. The result is that all black holes eventually explode! Hawking radiation is still at the very forefront of theoretical physics. There are raging debates about how Hawking radiation actually works, and whether it somehow carries away the information of how the black hole was formed. One of the greatest mysteries in physics is what is left behind after Hawking radiation causes a black hole to fully evaporate.
I met Hawking a few times over the years, including at the University of Cambridge and the University of Chicago. In addition to scientific discussions, I participated in Stephen Hawking's Universe, a six-part TV documentary about the birth and evolution of the universe, black holes, and other important aspects of modern cosmology. One of my most memorable interactions with him was from when I was a post-doctoral fellow at the Kavli Institute for Cosmological Physics in Santa Barbara. Hawking visited and sat across the hall from me for two weeks. It was wonderful to spend an extended period of time with him and appreciate his insights, intuition, and, especially, his humor.
One memory is particularly vivid: I described a project I had been working on for months; it had to do with how light travels in the universe. After listening politely, he responded with several statements I initially found inscrutable. I went back to my office somewhat deflated; it seemed clear he hadn't understood what I had been describing. But I continued to contemplate his comments and over the course of the ensuing weeks it slowly dawned on me that not only had he understood, but he had jumped way past me, providing signposts, far off in the distance, that pointed toward a deeper understanding of the subject. It took me months to fully discover and appreciate the entire meaning of his comments.
When he wasn't exploring the far reaches of the universe, Hawking actively engaged with the here and now. His was a voice that transcended politics, urging us to fully appreciate the world around us and to maintain a healthy perspective, given the immensity of the cosmos. In his later years, Hawking became increasingly alarmed about the potential for human-induced global catastrophe. He helped found the Breakthrough Starshot initiative to try to develop prototypes for interstellar travel; part of his motivation was to develop a back-up plan if the Earth becomes inhospitable. He also joined the Board of Sponsors of the Bulletin of Atomic Scientists and was a particularly vital and valued member. When the Bulletin moved the minute hand of the Doomsday Clock closer to midnight in 2007, Hawking said, "As scientists, we understand the dangers of nuclear weapons and their devastating effects, and we are learning how human activities and technologies are affecting climate systems in ways that may forever change life on Earth. As citizens of the world, we have a duty to alert the public to the unnecessary risks that we live with every day, and to the perils we foresee if governments and societies do not take action now to render nuclear weapons obsolete and to prevent further climate change."
The ensuing decade has made Hawking's exhortation ever more relevant and urgent. We ignore him at our peril.
Hawking has left the universe a much more interesting place than he found it.
Daniel Holz is an Associate Professor in Physics, Astronomy & Astrophysics, the Enrico Fermi Institute, and the Kavli Institute for Cosmological Physics, at the University of Chicago. His research focuses on general relativity in the context of astrophysics and cosmology. He is a member of the Laser Interferometer Gravitational-Wave Observatory (LIGO) collaboration, and was part of the team that announced the first detection of gravitational waves in early 2016. He received a 2012 National Science Foundation CAREER Award, the 2015 Quantrell Award for Excellence in Undergraduate Teaching, and the Breakthrough Prize in Fundamental Physics in 2016, and was selected as a Kavli Fellow of the National Academy of Sciences in 2017. Holz received his PhD in physics from the University of Chicago and his AB in physics from Princeton University.
Department members: Daniel E. Holz
Astrophysicists settle century-old cosmic debate on magnetism of planets and stars
February 9, 2018
UChicago News, by Rob Mitchum
Laser experiments verify 'turbulent dynamo' theory of how cosmic magnetic fields are created
The universe is highly magnetic, with everything from stars to planets to galaxies producing their own magnetic fields. Astrophysicists have long puzzled over these surprisingly strong and long-lived fields, with theories and simulations seeking a mechanism that explains their generation.
Using one of the world's most powerful laser facilities, a team led by University of Chicago scientists experimentally confirmed one of the most popular theories for cosmic magnetic field generation: the turbulent dynamo. By creating a hot turbulent plasma the size of a penny, which lasts a few billionths of a second, the researchers recorded how the turbulent motions can amplify a weak magnetic field to the strengths of those observed in our sun, distant stars and galaxies.
The paper, published this week in Nature Communications, is the first laboratory demonstration of a theory explaining the magnetic field of numerous cosmic bodies, which has been debated by physicists for nearly a century. Using the FLASH physics simulation code, developed by the Flash Center for Computational Science at UChicago, the researchers designed an experiment conducted at the OMEGA Laser Facility in Rochester, N.Y. to recreate turbulent dynamo conditions.
Confirming decades of numerical simulations, the experiment revealed that turbulent plasma could dramatically boost a weak magnetic field up to the magnitude observed by astronomers in stars and galaxies.
"We now know for sure that turbulent dynamo exists, and that it's one of the mechanisms that can actually explain magnetization of the universe," said Petros Tzeferacos, research assistant professor of astronomy and astrophysics at the University of Chicago and associate director of the Flash Center. "This is something that we hoped we knew, but now we do."
A mechanical dynamo produces an electric current by rotating coils through a magnetic field. In astrophysics, dynamo theory proposes the reverse: the motion of electrically-conducting fluid creates and maintains a magnetic field. In the early 20th century, physicist Joseph Larmor proposed that such a mechanism could explain the magnetism of the Earth and sun, inspiring decades of scientific debate and inquiry.
While numerical simulations demonstrated that turbulent plasma can generate magnetic fields at the scale of those observed in stars, planets and galaxies, creating a turbulent dynamo in the laboratory was far more difficult. Confirming the theory requires producing plasma at an extremely high temperature and volatility to produce the sufficient turbulence to fold, stretch and amplify the magnetic field.
To design an experiment that creates those conditions, Tzeferacos and colleagues at UChicago and the University of Oxford ran hundreds of two- and three-dimensional simulations with FLASH on the Mira supercomputer at Argonne National Laboratory. The final setup involved blasting two penny-sized pieces of foil with powerful lasers, propelling two jets of plasma through grids and into collision with each other, creating turbulent fluid motion.
"People have dreamed of doing this experiment with lasers for a long time, but it really took the ingenuity of this team to make this happen," said Donald Lamb, the Robert A. Millikan Distinguished Service Professor Emeritus in Astronomy and Astrophysics and director of the Flash Center. "This is a huge breakthrough."
The team also used FLASH simulations to develop two independent methods for measuring the magnetic field produced by the plasma: proton radiography, the subject of a recent paper from the FLASH group, and polarized light, based on how astronomers measure the magnetic fields of distant objects. Both measurements tracked the growth in mere nanoseconds of the magnetic field from its weak initial state to over 100 kiloGauss - stronger than a high-resolution MRI scanner and a million times stronger than the magnetic field of the Earth.
"This work opens up the opportunity to experimentally verify ideas and concepts about the origin of magnetic fields in the universe that have been proposed and studied theoretically over the better part of a century," said Fausto Cattaneo, professor of astronomy and astrophysics at the University of Chicago and a co-author of the paper.
Now that a turbulent dynamo can be created in a laboratory, scientists can explore deeper questions about its function: How quickly does the magnetic field increase in strength? How strong can the field get? How does the magnetic field alter the turbulence that amplified it?
"It's one thing to have well-developed theories, but it's another thing to really demonstrate it in a controlled laboratory setting where you can make all these kinds of measurements about what's going on," Lamb said. "Now that we can do it, we can poke it and probe it."
In addition to Tzeferacos and Lamb, UChicago co-authors on the paper include Carlo Graziani and Gianluca Gregori, who is also professor of physics at the University of Oxford. The research was funded by the European Research Council and the U.S. Department of Energy.
Department members: Fausto Cattaneo, Carlo Graziani, Donald Q. Lamb, Petros Tzeferacos
Scientific projects: Flash Center for Computational Science
Award honors Prof. Eugene Parker's lifetime of physics research
February 1, 2018
UChicago News, by Louise Lerner
Prof. Emeritus Eugene Parker's ideas were once widely questioned in the physics world. This week, he will receive one of the field's highest honors.
Parker will receive the American Physical Society's Medal for Exceptional Achievement in Research at a Feb. 1 ceremony in Washington, D.C. The medal citation notes Parker's "fundamental contributions to space physics, plasma physics, solar physics and astrophysics for over 60 years."
"I've been a member of the APS since 1952, so this is a nice honor," said Parker, the S. Chandrasekhar Distinguished Service Professor Emeritus in Physics at the University of Chicago. "I'm very pleased, particularly since people were skeptical about these concepts for a long time."
Early in his career Parker proposed a theory that faced widespread skepticism - notably that a "solar wind" was carrying charged particles from the surface of the sun to the far reaches of the solar system. Beginning with the Mariner II space probe to Venus in 1962, however, measurements from spacecraft began to validate his predictions.
In addition to the solar wind, he has investigated magnetic fields, including the role played by cosmic rays in Milky Way magnetic fields and how cyclonic turbulence generates magnetic fields.
"Gene Parker has a wonderful and exceptional record of seminal contributions to solar, space and astrophysics over the many years of his distinguished career," said Roger Falcone, chair of the 2018 APS Medal selection committee. "It is remarkable to see so many effects that bear his name."
It's been an eventful year for Parker, whom NASA honored in May 2017 by naming its first mission to send a spacecraft through the sun's corona after the professor. The Parker Solar Probe, which recently embarked on its thermal testing phase to be frozen and then blasted with heat to simulate conditions on its journey, is scheduled to launch in July 2018. It is the first spacecraft to be named after a living person.
Scientists are eager to explore the surface of the sun, especially as flares, winds and ejections from the sun can affect electronics and infrastructure here on Earth.
Parker said he plans to travel to witness the probe's launch this summer. He's looking forward to it; he's never seen a rocket launch. "I imagine it's like the Taj Mahal," he said. "Everyone's seen a picture of it, but to see it in person is a completely different story."
Department members: Eugene N. Parker
Astronomy faculty member Bob Rosner participates in Atomic Bulletin of Scientists Doomsday Clock news conference
January 26, 2018
New York Times, by Sewall Chan
The Doomsday Clock, a potent symbol of scientific concerns about humanity's possible annihilation, was advanced by 30 seconds on Thursday, to 2 minutes to midnight, the Bulletin of the Atomic Scientists announced in Washington.
The last time the clock was moved so close to midnight was in 1953, during the Cold War.
"In 2017, world leaders failed to respond effectively to the looming threats of nuclear war and climate change, making the world security situation more dangerous than it was a year ago - and as dangerous as it has been since World War II," the bulletin's science and security board, which oversees the clock, said in a statement.
Department members: Robert Rosner
Dark Energy Survey finds remains of 11 galaxies eaten by the Milky Way
January 16, 2018
Scientific collaboration including UChicago and labs releases three years of data
Scientists have released the preliminary cosmological findings from the Dark Energy Survey - research on about 400 million astronomical objects, including distant galaxies as well as stars in our own galaxy.
Among the highlights of the first three years of survey data, presented Jan. 10 during the American Astronomical Society meeting in Washington, D.C., is the discovery of 11 new stellar streams - remnants of smaller galaxies torn apart and devoured by our Milky Way.
The results were announced by the Dark Energy Survey, an international collaboration of more than 400 members including scientists from UChicago, Argonne and Fermilab, that aims to reveal the nature of the mysterious force of dark energy.
The public release fulfills a commitment scientists on the survey made to share their findings with the astronomy community and the public. The data cover about 5,000 square degrees, or one-eighth of the entire sky, and include roughly 40,000 exposures taken with the Dark Energy Camera. The images correspond to hundreds of terabytes of data and are being released along with catalogs of hundreds of millions of galaxies and stars.
"There are all kinds of discoveries waiting to be found in the data," said Brian Yanny of Fermi National Accelerator Laboratory, Dark Energy Survey data management project scientist. "While DES scientists are focused on using it to learn about dark energy, we wanted to enable astronomers to explore these images in new ways, to improve our understanding of the universe."
The Dark Energy Camera, the primary observation tool of the Dark Energy Survey, is one of the most powerful digital imaging devices in existence. It was built and tested at UChicago-affiliated Fermilab, the lead laboratory on the Dark Energy Survey, and is mounted on the National Science Foundation's 4-meter Blanco telescope in Chile. The DES images are processed by a team at the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign.
One new discovery enabled by the data set is the detection of 11 new streams of stars around our Milky Way. Our home galaxy is surrounded by a massive halo of dark matter, which exerts a powerful gravitational pull on smaller, nearby galaxies. The Milky Way grows by pulling in, ripping apart and absorbing these smaller systems. As stars are torn away, they form streams across the sky that can be detected using the Dark Energy Camera. Even so, stellar streams are extremely difficult to find since they are composed of relatively few stars spread out over a large area of sky.
"It's exciting that we found so many stellar streams," said astrophysicist Alex Drlica-Wagner of Fermilab and the Kavli Institute for Cosmological Physics at UChicago. "We can use these streams to measure the amount, distribution and 'clumpiness' of dark matter in the Milky Way. Studies of stellar streams will help constrain the fundamental properties of dark matter."
Prior to the new discoveries, only about two dozen stellar streams had been discovered. Many of them were found by the Sloan Digital Sky Survey, a precursor to the Dark Energy Survey. The effort to detect new stellar streams in the Dark Energy Survey was led by University of Chicago graduate student Nora Shipp.
"We're interested in these streams because they teach us about the formation and structure of the Milky Way and its dark matter halo. Stellar streams give us a snapshot of a larger galaxy being built out of smaller ones," said Shipp. "These discoveries are possible because DES is the widest, deepest and best-calibrated survey out there."
Since there is no universally accepted naming convention for stellar streams, the Dark Energy Survey has reached out to schools in Chile and Australia, asking young students to select names. Students and their teachers have worked together to name the streams after aquatic words in native languages from northern Chile and aboriginal Australia.
Funding: U.S. Department of Energy Office of Science, National Science Foundation
- This release was originally posted on the Fermi National Accelerator Laboratory website.
Department members: Joshua A. Frieman
Department students: Nora Shipp
Scientific projects: Dark Energy Survey
Computational astrophysics team uncloaks magnetic fields of cosmic events
January 4, 2018
UChicago News, by Rob Mitchum
New method enhances study of stars, black holes in laboratory settings
The development of ultra-intense lasers delivering the same power as the entire U.S. power grid has enabled the study of cosmic phenomena such as supernovae and black holes in earthbound laboratories. Now, a new method developed by computational astrophysicists at the University of Chicago allows scientists to analyze a key characteristic of these events: their powerful and complex magnetic fields.
In the field of high-energy density physics, or HEDP, scientists study a wide range of astrophysical objects -- stars, supermassive black holes at the center of galaxies and galaxy clusters -- with laboratory experiments as small as a penny and lasting only a few billionths of a second. By focusing powerful lasers on a carefully designed target, researchers can produce plasmas that reproduce conditions observed by astronomers in our sun and distant galaxies.
Planning these complex and expensive experiments requires large-scale, high-fidelity computer simulation beforehand. Since 2012, the Flash Center for Computational Science of the Department of Astronomy & Astrophysics at UChicago has provided the leading open computer code, called FLASH, for these HEDP simulations, enabling researchers to fine-tune experiments and develop analysis methods before execution at sites such as the National Ignition Facility at Lawrence Livermore National Laboratory or the OMEGA Laser Facility in Rochester, N.Y.
"As soon as FLASH became available, there was kind of a stampede to use it to design experiments," said Petros Tzeferacos, research assistant professor of astronomy and astrophysics and associate director of the Flash Center.
During these experiments, laser probe beams can provide researchers with information about the density and temperature of the plasma. But a key measurement, the magnetic field, has remained elusive. To try and tease out magnetic field measurements from extreme plasma conditions, scientists at MIT developed an experimental diagnostic technique that uses charged particles instead, called proton radiography.
In a new paper for the journal Review of Scientific Instruments, Flash Center scientists Carlo Graziani, Donald Lamb and Tzeferacos, with MIT's Chikang Li, describe a new method for acquiring quantitative, high-resolution information about these magnetic fields. Their discovery, refined using FLASH simulations and real experimental results, opens new doors for understanding cosmic phenomena.
"We chose to go after experiments motivated by astrophysics where magnetic fields were important," said Lamb, the Robert A. Millikan Distinguished Service Professor Emeritus in Astronomy & Astrophysics and director of the Flash Center. "The creation of the code plus the need to try to figure out how to understand what magnetic fields are created caused us to build this software, that can for the first time quantitatively reconstruct the shape and strength of the magnetic field."
In proton radiography, energetic protons are shot through the magnetized plasma towards a detector on the other side. As the protons pass through the magnetic field, they are deflected from their path, forming a complex pattern on the detector. These patterns were difficult to interpret, and previous methods could only make general statements about the field's properties.
"Magnetic fields play important roles in essentially almost every astrophysical phenomena. If you aren't able to actually look at what's happening, or study them, you're missing a key part of almost every astrophysical object or process that you're interested in," said Tzeferacos.
By conducting simulated experiments with known magnetic fields, the Flash Center team constructed an algorithm that can reconstruct the field from the proton radiograph pattern. Once calibrated computationally, the method was applied to experimental data collected at laser facilities, revealing new insights about astrophysical events.
The combination of the FLASH code, the development of the proton radiography diagnostic, and the ability to reconstruct magnetic fields from the experimental data, are revolutionizing laboratory plasma astrophysics and HEDP. "The availability of these tools has caused the number of HEDP experiments that study magnetic fields to skyrocket," said Lamb.
The new software for magnetic field reconstruction, called PRaLine, will be shared with the community both as part of the next FLASH code release and as a separate component available on GitHub. Lamb and Tzeferacos said they expect it to be used for studying many astrophysics topics, such as the annihilation of magnetic fields in the solar corona; astrophysical jets produced by young stellar objects, the Crab Nebula pulsar, and the supermassive black holes at the center of galaxies; and the amplification of magnetic fields and acceleration of cosmic rays by shocks in supernova remnants.
"The types of experiments HEDP scientists perform now are very diverse," said Tzeferacos. "FLASH contributed to this diversity, because it enables you to think outside the box, try different simulations of different configurations, and see what plasma conditions you are able to achieve."
The paper, "Inferring Morphology and Strength of Magnetic Fields From Proton Radiographs," was published online by Review of Scientific Instruments. The work was funded by grants from the U.S. Department of Energy and the National Science Foundation.
Department members: Carlo Graziani, Donald Q. Lamb, Petros Tzeferacos
Scientific projects: Flash Center for Computational Science
The Solar System Could Have Formed in a Bubble Surrounding One of the Hottest Stars
December 22, 2017
Popular Mechanics, by Jay Bennett
A new theory of the solar system's formation provides an alternative to the idea our system formed from a supernova.
The prevailing theory of the formation of the solar system is that a large supernova ejected material that formed a dense cloud of interstellar dust, which then collapsed to form our sun - as well as other stars that have since drifted away - and the leftover material orbits our host star as planets, moons, asteroids and the rest. Astronomers developed this theory because of the high abundance the isotope aluminum-26, which is liberally ejected in a supernova explosion.
However, more recent measurements of meteorites from the early solar system suggest there is not as much iron-60 as in the rest of the galaxy, which is also created in high abundances in supernovae. "It begs the question of why one was injected into the solar system and the other was not," said coauthor Vikram Dwarkadas, a research associate professor in Astronomy and Astrophysics at the University of Chicago, in a press release.
Dwarkadas and his team have developed a new solar system formation theory in a study published in today in the Astrophysical Journal, one that could explain the apparent imbalance of aluminum-26 and iron-60 compared to what you would expect to see from supernova material.
The new theory suggests that the sun formed within the walls of a dense bubble of material surrounding one of the hottest-burning stars in the galaxy, a Wolf-Rayet star. Wolf-Rayet stars are rare and diverse stars full of heavy elements that tower about 50 times larger than our sun. Their surfaces burn at temperatures ranging from 30,000 K to more than 200,000 K (50,000 to 360,000F), making them hotter and brighter than almost all other stars.
The immense heat and volatile conditions cause Wolf-Rayet stars to hemorrhage heavy elements out into space. These stars with hundreds of times the mass of our sun are short-lived, only lasting for millions of years compared to the 4.6-billion-year-old sun, which still has about 5 billion years to go. They quickly burn through any hydrogen as Red Supergiants, and then begin fusing helium and other heavier elements as Wolf-Rayets, all the way up to iron by the end. These heavy elements bubble up to the surface in large amounts, where vicious stellar winds rip them up and eject them into space.
A bubble with a thin dense shell of heavy material forms around the raging star, inflated by stellar winds. These bubbles vary in size based on the initial mass of the star, but they can stretch as big as tens of parsecs in diameter with the volatile star in the middle. The new theory suggests that the sun could have formed within the walls of this immense cosmic bubble, where the high densities cause rapid star formation.
"These are really large, and the sun's radius is very small compared to the bubble size," Dwarkadas told Popular Mechanics in an email. "We postulate that a part of the shell will collapse to form the early solar system."
Department members: Vikram Dwarkadas
Scientists describe how solar system could have formed in bubble around giant star
December 22, 2017
UChicago News, by Louise Lerner
Despite the many impressive discoveries humans have made about the universe, scientists are still unsure about the birth story of our solar system.
Scientists with the University of Chicago have laid out a comprehensive theory for how our solar system could have formed in the wind-blown bubbles around a giant, long-dead star. Published Dec. 22 in the Astrophysical Journal, the study addresses a nagging cosmic mystery about the abundance of two elements in our solar system compared to the rest of the galaxy.
The general prevailing theory is that our solar system formed billions of years ago near a supernova. But the new scenario instead begins with a giant type of star called a Wolf-Rayet star, which is more than 40 to 50 times the size of our own sun. They burn the hottest of all stars, producing tons of elements which are flung off the surface in an intense stellar wind. As the Wolf-Rayet star sheds its mass, the stellar wind plows through the material that was around it, forming a bubble structure with a dense shell.
A simulation shows how stellar winds carry mass from a giant star over the course of millions of years, forming bubbles around it - which could have served as the origins of our solar system. Simulation by V. Dwarkadas/D. Rosenberg. Click here for more info.
"The shell of such a bubble is a good place to produce stars," because dust and gas become trapped inside where they can condense into stars, said coauthor Nicolas Dauphas, professor in the Department of Geophysical Sciences. The authors estimate that 1 percent to 16 percent of all sun-like stars could be formed in such stellar nurseries.
This setup differs from the supernova hypothesis in order to make sense of two isotopes that occur in strange proportions in the early solar system, compared to the rest of the galaxy. Meteorites left over from the early solar system tell us there was a lot of aluminium-26. In addition, studies, including a 2015 one by Dauphas and a former student, increasingly suggest we had less of the isotope iron-60.
This brings scientists up short, because supernovae produce both isotopes. "It begs the question of why one was injected into the solar system and the other was not," said coauthor Vikram Dwarkadas, a research associate professor in Astronomy and Astrophysics.
This brought them to Wolf-Rayet stars, which release lots of aluminium-26, but no iron-60.
"The idea is that aluminum-26 flung from the Wolf-Rayet star is carried outwards on grains of dust formed around the star. These grains have enough momentum to punch through one side of the shell, where they are mostly destroyed - trapping the aluminum inside the shell," Dwarkadas said. Eventually, part of the shell collapses inward due to gravity, forming our solar system.
As for the fate of the giant Wolf-Rayet star that sheltered us: Its life ended long ago, likely in a supernova explosion or a direct collapse to a black hole. A direct collapse to a black hole would produce little iron-60; if it was a supernova, the iron-60 created in the explosion may not have penetrated the bubble walls, or was distributed unequally.
Other authors on the paper included UChicago undergraduate student Peter Boyajian and Michael Bojazi and Brad Meyer of Clemson University.
Citation: "Triggered star formation inside the shell of a Wolf-Rayet bubble as the origin of the solar system." The Astrophysical Journal, Dec. 22, 2017.
Department members: Vikram Dwarkadas
First multimessenger observation of a neutron-star merger is Physics World 2017 Breakthrough of the Year
December 18, 2017
The Physics World 2017 Breakthrough of the Year goes to the international team of astronomers and astrophysicists that ushered in a new era of astronomy by making the first ever multimessenger observation involving gravitational waves.
On 17 August 2017 the LIGO-Virgo gravitational-wave detectors, the Fermi Gamma-ray Space Telescope and the INTEGRAL gamma-ray space telescope detected nearly-simultaneous signals. They came from the merger of two neutron stars - an object now called GW 170817. This was the first time that LIGO-Virgo scientists had seen a neutron star merger, but five hours later they had already worked out the location of the source in the sky. Over the next hours and days, more than 70 telescopes were pointed at GW 170817 and a wealth of observations were made in the gamma-ray, X-ray, visible, infrared and radio portions of the electromagnetic spectrum. Astrophysicists also searched for neutrinos, but none were seen.
These coordinated observations have already provided a vast amount of information about what happens when neutron stars collide in what is called a "kilonova". The observations have yielded important clues about how heavy elements, such as gold, are produced in the universe. The ability to measure both gravitational waves and visible light from neutron-star mergers has also given a new and independent way of measuring the expansion rate of the universe. In addition, the observation settles a long-standing debate about the origin of short, high-energy, gamma-ray bursts.
Department members: Daniel E. Holz
Scientific projects: Laser Interferometer Gravitational-wave Observatory
Auger result in the list of scientific breakthroughs of the year
December 18, 2017
The Physics World top 10 breakthroughs of 2017 is awarded to the Pierre Auger Observatory collaboration for showing that ultra-high-energy cosmic rays come from outside the Milky Way. For decades, astrophysicists have believed that the sources of cosmic rays with energies greater than about 1 EeV (1018eV) could be worked out from the arrival directions of these particles. This is unlike lower energy cosmic rays, which appear to come from all directions after being deflected by the Milky Way's magnetic fields. Now, Pierre Auger's 1600 Cherenkov particle detectors in Argentina have revealed that the arrival rate of ultra-high-energy cosmic rays is greater in one half of the sky. What is more, the excess lies away from the centre of the Milky Way - suggesting that the cosmic rays have extra-galactic origins.
Department members: Angela V. Olinto, Paolo Privitera
Scientific projects: Pierre Auger Observatory
ALMA follow up of SPT discovered galaxies
December 12, 2017
ALMA finds massive primordial galaxies swimming in vast ocean of dark matter
Astronomers expect that the first galaxies, those that formed just a few hundred million years after the Big Bang, would share many similarities with some of the dwarf galaxies we see in the nearby universe today. These early agglomerations of a few billion stars would then become the building blocks of the larger galaxies that came to dominate the universe after the first few billion years.
Ongoing observations with the Atacama Large Millimeter/submillimeter Array (ALMA), however, have discovered surprising examples of massive, star-filled galaxies seen when the cosmos was less than a billion years old. This suggests that smaller galactic building blocks were able to assemble into large galaxies quite quickly.
The latest ALMA observations push back this epoch of massive-galaxy formation even further by identifying two giant galaxies seen when the universe was only 780 million years old, or about 5 percent its current age. ALMA also revealed that these uncommonly large galaxies are nestled inside an even-more-massive cosmic structure, a halo of dark matter several trillion times more massive than the sun.
The two galaxies are in such close proximity - less than the distance from the Earth to the center of our galaxy - that they will shortly merge to form the largest galaxy ever observed at that period in cosmic history. This discovery provides new details about the emergence of large galaxies and the role that dark matter plays in assembling the most massive structures in the universe.
The researchers report their findings in the journal Nature ("Galaxy growth in a massive halo in the first billion years of cosmic history").
"With these exquisite ALMA observations, astronomers are seeing the most massive galaxy known in the first billion years of the universe in the process of assembling itself," said Dan Marrone, associate professor of astronomy at the University of Arizona in Tucson and lead author on the paper.
Astronomers are seeing these galaxies during a period of cosmic history known as the Epoch of Reionization, when most of intergalactic space was suffused with an obscuring fog of cold hydrogen gas. As more stars and galaxies formed, their energy eventually ionized the hydrogen between the galaxies, revealing the universe as we see it today.
"We usually view that as the time of little galaxies working hard to chew away at the neutral intergalactic medium," said Marrone. "Mounting observational evidence with ALMA, however, has helped to reshape that story and continues to push back the time at which truly massive galaxies first emerged in the universe."
The galaxies that Marrone and his team studied, collectively known as SPT0311-58, were originally identified as a single source by the South Pole Telescope. These first observations indicated that this object was very distant and glowing brightly in infrared light, meaning that it was extremely dusty and likely going through a burst of star formation. Subsequent observations with ALMA revealed the distance and dual nature of the object, clearly resolving the pair of interacting galaxies.
To make this observation, ALMA had some help from a gravitational lens, which provided an observing boost to the telescope. Gravitational lenses form when an intervening massive object, like a galaxy or galaxy cluster, bends the light from more distant galaxies. They do, however, distort the appearance of the object being studied, requiring sophisticated computer models to reconstruct the image as it would appear in its unaltered state.
This "de-lensing" process provided intriguing details about the galaxies, showing that the larger of the two is forming stars at a rate of 2,900 solar masses per year. It also contains about 270 billion times the mass of our sun in gas and nearly 3 billion times the mass of our sun in dust. "That's a whopping large quantity of dust, considering the young age of the system," noted Justin Spilker, a recent graduate of the University of Arizona and now a postdoctoral fellow at the University of Texas at Austin.
The astronomers determined that this galaxy's rapid star formation was likely triggered by a close encounter with its slightly smaller companion, which already hosts about 35 billion solar masses of stars and is increasing its rate of starburst at the breakneck pace of 540 solar masses per year.
The researchers note that galaxies of this era are "messier" than the ones we see in the nearby universe. Their more jumbled shapes would be due to the vast stores of gas raining down on them and their ongoing interactions and mergers with their neighbors.
The new observations also allowed the researchers to infer the presence of a truly massive dark matter halo surrounding both galaxies. Dark matter provides the pull of gravity that causes the universe to collapse into structures (galaxies, groups and clusters of galaxies, etc.).
"If you want to see if a galaxy makes sense in our current understanding of cosmology, you want to look at the dark matter halo - the collapsed dark matter structure - in which it resides," said Chris Hayward, associate research scientist at the Center for Computational Astrophysics at the Flatiron Institute in New York City. "Fortunately, we know very well the ratio between dark matter and normal matter in the universe, so we can estimate what the dark matter halo mass must be."
By comparing their calculations with current cosmological predictions, the researchers found that this halo is one of the most massive that should exist at that time.
"There are more galaxies discovered with the South Pole Telescope that we're following up on," said Joaquin Vieira of the University of Illinois at Urbana-Champaign, "and there is a lot more survey data that we are just starting to analyze. Our hope is to find more objects like this, possibly even more distant ones, to better understand this population of extreme dusty galaxies and especially their relation to the bulk population of galaxies at this epoch."
"In any case, our next round of ALMA observations should help us understand how quickly these galaxies came together and improve our understanding of massive galaxy formation during reionization," added Marrone.
Department members: John E. Carlstrom, Thomas Crawford
Scientific projects: South Pole Telescope
Three UChicago faculty members named AAAS fellows
November 21, 2017
UChicago News, by Louise Lerner
Three members of the University of Chicago faculty were named as 2017 fellows of the American Association for the Advancement of Science. Fellows are elected by AAAS members for their scientifically or socially distinguished efforts to advance science and its applications.
Don Q. Lamb, the Robert A. Millikan Distinguished Service Professor of Astronomy and Astrophysics and the College, was named "for outstanding contributions to theoretical astrophysics, especially for seminal contributions to the understanding of supernovae and for leadership in the Sloan Digital Sky Survey."
His research interests have included the properties of matter at high densities and temperatures, the evolution of white dwarfs and neutron stars, gamma-ray bursts, supernovae and most recently, experiments that use intense lasers to study the origin of the magnetic fields in the universe. He played a key role in founding the Sloan Digital Sky Survey and was the co-leader and Mission Scientist for the NASA High Energy Transient Explorer. Head of the Flash Center for Computational Science, Lamb is also affiliated with the Enrico Fermi Institute, the Energy Policy Institute of Chicago and the Harris School of Public Policy.
Department members: Donald Q. Lamb
Scientific projects: Flash Center for Computational Science