Department in the News
Eugene Parker on first year of namesake NASA mission: "It's pretty exciting stuff"
August 13, 2019
A year after the launch of Parker Solar Probe, NASA scientist Nicola Fox sits down with the mission's namesake, Prof. Emeritus Eugene Parker, to discuss their findings so far.
Click on the image to enlarge
UChicago News, by Louise Lerner
Pioneering UChicago astrophysicist looks back at historic launch of solar probe

Prof. Eugene Parker had never seen a NASA launch in person until Aug. 12, 2018 - when a spacecraft honoring the pioneering University of Chicago astrophysicist blazed through the predawn skies, beginning its ambitious mission to the sun.

Six decades after Parker wrote a groundbreaking paper that shaped how we view the solar system, the launch of Parker Solar Probe was not only historic but also emotional for the 92-year-old scientist.

"So much has gone into this launch, and then to see it all disappear slowly - fading away into the night sky, knowing it will never come back - it was a moving experience," Parker said.

In the year since, Parker has been receiving updates on the NASA mission, which has already come closer to the sun than any spacecraft. Parker recently visited with Nicky Fox, director of NASA's Heliophysics Division at NASA Headquarters in Washington, at his Hyde Park apartment and learned that the spacecraft is running perfectly - and has gathered twice as much data as originally predicted.

"Parker Solar Probe is blazing a trail as she orbits through the corona; she's behaving beautifully," said Fox. "We're actually very excited because we have more than twice as much data as we had expected."

Parker Solar Probe has circled the sun twice thus far, and on Sept. 1 will reach its closest point to the star yet.

"It's pretty exciting stuff," said Parker, who is the only living person to have a NASA mission named after them.

The spacecraft, built by Johns Hopkins Applied Physics Laboratory to withstand the intense heat and radiation coming off the sun, is a marvel of engineering. It is the fastest-moving object built by humans, traveling at more than 150,000 miles per hour. It must constantly orient itself to keep its shield - a four-and-a-half inch-thick slab of carbon composite that can withstand the 2,500-degree Fahrenheit temperatures - between itself and the star. (Except for one especially tough instrument, built by UChicago alum Justin Kasper, which peeks around the edge of the craft to scoop up particles of the solar wind).

Fascinating every step of the way
Parker Solar Probe will come closer than any other spacecraft to the sun, seeking to understand multiple mysteries about our star - such as why the corona around the sun is actually hotter than the surface of the sun itself.

"You rarely have a space mission that doesn't come up with the unexpected, and it's actually going to get more exciting as the mission goes on and crosses into regions that spacecraft have never been in before," Parker said. "It's just fascinating every step of the way."

These questions have their origins in a revolutionary 1958 paper authored by Parker, which claimed that the sun was expelling waves of particles in every direction. Though the idea was roundly rejected by the scientific community at first, we now know this phenomenon, which Parker called the solar wind, shapes the entire solar system.

"A lot of people don't realize that space is not just empty space - it's full of this constantly active plasma that is carrying the magnetic field from the sun towards us and forming a protective bubble around the solar system," Fox said. "When something happens on the sun, we feel the impact here on Earth, and it was all predicted by Eugene Parker."

Scientists also hope to use Parker Solar Probe's observations to better predict solar flares and to understand how to protect future astronauts traveling through space who would encounter solar radiation.

Early answers may lie in the 22 gigabytes of data Parker Solar Probe collected during its first two encounters with the sun, but as Parker said: "I wouldn't be surprised if the most surprising things have yet to come."

Related:
Department members: Eugene N. Parker

New measure of Hubble constant adds to mystery about universe's expansion rate
July 16, 2019
Click on the image to enlarge
UChicago News, by Louise Lerner
Prof. Wendy Freedman leads study of red giant stars for new measurement of disputed constant
University of Chicago scientists have made a new measurement of how fast the universe is expanding - using an entirely different kind of star than previous endeavors. That value falls in the center of a hotly debated question in astrophysics that may call for an entirely new model of the universe.

Scientists have known for almost a century that the universe is expanding, but the exact number for how fast it's going has remained stubbornly elusive. In 2001, Prof. Wendy Freedman led a team that used distant stars to make a landmark measurement of this number, called the Hubble constant - but it disagrees with another major measurement, and the tension between the two numbers has persisted even as each side makes more and more accurate readings.

In a new paper to be published shortly in the Astrophysical Journal, Freedman and her team announced a new measurement of the Hubble constant using a kind of star known as a red giant. Their observations, made with NASA's Hubble Space Telescope, indicate that the expansion rate for our corner of the universe is just under 70 kilometers per second per megaparsec - slightly smaller than their previous measurement, but not alleviating the tension.

"The Hubble constant is the cosmological parameter that sets the absolute scale, size and age of the universe; it is one of the most direct ways we have of quantifying how the universe evolves," said Freedman, the John and Marion Sullivan University Professor in Astronomy and Astrophysics and a world-renowned astronomer. "The discrepancy that we saw before has not gone away, but this new evidence suggests that the jury is still out on whether there is an immediate and compelling reason to believe that there is something fundamentally flawed in our current model of the universe."

A number behind the theory of the universe
The Hubble constant, named after pioneering astronomer and UChicago alum Edwin Hubble, underpins everything in the universe - from our estimate of when the Big Bang happened to how much dark matter exists. It helps scientists sketch out a theory of the history and structure of the universe; and conversely, if there are fault lines in that theory, an accurate measurement of the Hubble constant might lead them to it.

"The Hubble constant...is one of the most direct ways we have of quantifying how the universe evolves."
- Prof. Wendy Freedman

Twenty years ago, the Hubble Space Telescope Key Project team, which Freedman led, announced it had measured the value using distant stars called Cepheids, which pulse at regular intervals. Their program concluded that the value of the Hubble constant for our universe was 72. As astronomers have refined their analyses and gathered new data, this number has remained fairly stable, at about 73.

But more recently, scientists took a very different approach: building a model based on the rippling structure of light left over from the earliest moments of the Big Bang, which is called the Cosmic Microwave Background. If they ran a model forward in time, extrapolating from the first few moments of the universe, they reached a value of 67. That disagreement is significant - nearly 10 percent - and it has continued to solidify over time.

Both camps have looked for anything that might be causing the mismatch. "Naturally, questions arise as to whether the discrepancy is coming from some aspect that astronomers don't yet understand about the stars we're measuring, or whether our cosmological model of the universe is still incomplete," Freedman said. "Or maybe both need to be improved upon."

Mapping the stars
A central part of the challenge in measuring the universe is that it is very difficult to accurately calculate distances to distant objects. Freedman's team originally looked at two types of stars that have reliable characteristics which allow astronomers to use them in combination as cosmological measuring sticks: Type Ia supernovae, which explode at a uniform brightness; and Cepheid variables, stars which pulse at regular intervals that can be matched to their peak brightnesses. But it's still possible that there is something about Cepheids that scientists don't yet fully understand, which could be introducing errors.

Freedman's team sought to check their results by establishing a new and entirely independent path to the Hubble constant using an entirely different kind of star.

Certain stars end their lives as a very luminous kind of star called a red giant. At a certain point, the star undergoes a catastrophic event called a helium flash, in which the temperature rises to about 100 million degrees and the structure of the star is rearranged, which ultimately dramatically decreases its luminosity. (This will one day happen to our own sun, which will also become a red giant). Astronomers can see the point where all the luminosities of the stars drop off, and they can use this as a way to tell distance.

"Our initial thought was that if there's a problem to be resolved between the Cepheids and the Cosmic Microwave Background, then the red giant method can be the tie-breaker," said Freedman.

"The principle is simple," Freedman said. "Imagine that you are standing near a street light that you know is 10 feet away. At regular intervals down the street you can seen more street lights, which get progressively dimmer the further away that they are. Knowing how far away and how bright the lamp is beside you, and then measuring how much fainter the more distant lamps appear to be, allows you to estimate the distances to each of the other lamps all down the road."

Freedman's team put this into action using sensitive cameras on the Hubble Space Telescope, searching for their new cosmic lampposts. By comparing the apparent luminosities of the distant red giants with nearby ones that we've measured with other methods, and pairing these readings with those from Type Ia supernovae, Freedman and her team were able to determine how far away each of the host galaxies were.

The next step is straightforward: How fast that galaxy is moving away from us is the product of its distance times the Hubble constant. Luckily, a galaxy's velocity is simple to measure - the light coming from galaxies shifts depending on how fast the galaxy is moving away from us.

Their calculations gave a Hubble constant of 69.8 - straddling the two previously determined numbers.

"The red giant method is independent of the Cepheids and is incredibly precise. The stars used are of lower mass, have different evolutionary histories and are located in different regions of distant galaxies," said Taylor Hoyt, a University of Chicago graduate student and co-author on the paper.

But the results do not appear to strongly favor one answer over the other.

"We are working at the frontier of what is currently known about cosmology," Freedman concluded. "These results suggest that we do not have the final answer yet. The burden of proof is high when claims of new physics hang in the balance, but that's what makes it exciting," she said. "Either way the conflict resolves, it is important. We either confirm our standard model of cosmology, or we learn something new about the universe."

The other University of Chicago co-author was Dylan Hatt, PhD'18. Carnegie scientist Barry Madore also has a visiting appointment at UChicago. Other co-authors included scientists with the Observatories of the Carnegie Institution for Science, Princeton University, Seoul National University, Penn State, Florida Atlantic University and the Leibniz Institute for Astrophysics-Potsdam.

Related:
Department members: Wendy L. Freedman, Barry Madore
Department students: Taylor Hoyt

New Hubble Constant Measurement Adds to Mystery of Universe's Expansion Rate
July 16, 2019
Click on the image to enlarge
hubblesite.org
Red Giant Stars Used as Milepost Markers
In 1924, American astronomer Edwin Hubble announced that he discovered galaxies outside of our Milky Way by using the powerful new Hooker telescope perched above Los Angeles. By measuring the distances to these galaxies, he realized the farther away a galaxy is, the faster it appears to be receding from us. This was incontrovertible evidence the universe is uniformly expanding in all directions. This was a big surprise, even to Albert Einstein, who predicted a well-balanced, static universe. The expansion rate is the basis of the Hubble constant. It is a sought-after value because it yields clues to the origin, age, evolution, and future fate of our universe.

For nearly the past century astronomers have worked meticulously to precisely measure the Hubble constant. Before the Hubble Space Telescope was launched in 1990, the universe's age was thought to lie between 10 and 20 billion years, based on different estimates of the Hubble constant. Improving this value was one of the biggest justifications for building the Hubble telescope. This paid off in the early 1990s when a team led by Wendy Freedman of the University of Chicago greatly refined the Hubble constant value to a precision of 10%. This was possible because the Hubble telescope is so sharp at finding and measuring Cepheid variable stars as milepost markers - just as Edwin Hubble did 70 years earlier.

But astronomers strive for ever greater precision, and this requires further refining yardsticks for measuring vast intergalactic distances of billions of light-years. Freedman's latest research looks at aging red giant stars in nearby galaxies. They are also milepost markers because they all reach the same peak brightness at a critical stage of their late evolution. This can be used to calculate distances.

Freedman's research is one of several recent studies that point to a nagging discrepancy between the universe's modern expansion rate and predictions based on the universe as it was more than 13 billion years ago, as measured by the European Space Agency's Planck satellite. This latest measurement offers new evidence suggesting that there may be something fundamentally flawed in the current model of the universe.

Astronomers have made a new measurement of how fast the universe is expanding, using an entirely different kind of star than previous endeavors. The revised measurement, which comes from NASA's Hubble Space Telescope, falls in the center of a hotly debated question in astrophysics that may lead to a new interpretation of the universe's fundamental properties.

Scientists have known for almost a century that the universe is expanding, meaning the distance between galaxies across the universe is becoming ever more vast every second. But exactly how fast space is stretching, a value known as the Hubble constant, has remained stubbornly elusive.

Now, University of Chicago professor Wendy Freedman and colleagues have a new measurement for the rate of expansion in the modern universe, suggesting the space between galaxies is stretching faster than scientists would expect. Freedman's is one of several recent studies that point to a nagging discrepancy between modern expansion measurements and predictions based on the universe as it was more than 13 billion years ago, as measured by the European Space Agency's Planck satellite.

As more research points to a discrepancy between predictions and observations, scientists are considering whether they may need to come up with a new model for the underlying physics of the universe in order to explain it.

"The Hubble constant is the cosmological parameter that sets the absolute scale, size and age of the universe; it is one of the most direct ways we have of quantifying how the universe evolves," said Freedman. "The discrepancy that we saw before has not gone away, but this new evidence suggests that the jury is still out on whether there is an immediate and compelling reason to believe that there is something fundamentally flawed in our current model of the universe."

In a new paper accepted for publication in The Astrophysical Journal, Freedman and her team announced a new measurement of the Hubble constant using a kind of star known as a red giant. Their new observations, made using Hubble, indicate that the expansion rate for the nearby universe is just under 70 kilometers per second per megaparsec (km/sec/Mpc). One parsec is equivalent to 3.26 light-years distance.

This measurement is slightly smaller than the value of 74 km/sec/Mpc recently reported by the Hubble SH0ES (Supernovae H0 for the Equation of State) team using Cepheid variables, which are stars that pulse at regular intervals that correspond to their peak brightness. This team, led by Adam Riess of the Johns Hopkins University and Space Telescope Science Institute, Baltimore, Maryland, recently reported refining their observations to the highest precision to date for their Cepheid distance measurement technique.

How to Measure Expansion
A central challenge in measuring the universe's expansion rate is that it is very difficult to accurately calculate distances to distant objects.

In 2001, Freedman led a team that used distant stars to make a landmark measurement of the Hubble constant. The Hubble Space Telescope Key Project team measured the value using Cepheid variables as distance markers. Their program concluded that the value of the Hubble constant for our universe was 72 km/sec/Mpc.

But more recently, scientists took a very different approach: building a model based on the rippling structure of light left over from the big bang, which is called the Cosmic Microwave Background. The Planck measurements allow scientists to predict how the early universe would likely have evolved into the expansion rate astronomers can measure today. Scientists calculated a value of 67.4 km/sec/Mpc, in significant disagreement with the rate of 74.0 km/sec/Mpc measured with Cepheid stars.

Astronomers have looked for anything that might be causing the mismatch. "Naturally, questions arise as to whether the discrepancy is coming from some aspect that astronomers don't yet understand about the stars we're measuring, or whether our cosmological model of the universe is still incomplete," Freedman said. "Or maybe both need to be improved upon."

Freedman's team sought to check their results by establishing a new and entirely independent path to the Hubble constant using an entirely different kind of star.

Certain stars end their lives as a very luminous kind of star called a red giant, a stage of evolution that our own Sun will experience billions of years from now. At a certain point, the star undergoes a catastrophic event called a helium flash, in which the temperature rises to about 100 million degrees and the structure of the star is rearranged, which ultimately dramatically decreases its luminosity. Astronomers can measure the apparent brightness of the red giant stars at this stage in different galaxies, and they can use this as a way to tell their distance.

The Hubble constant is calculated by comparing distance values to the apparent recessional velocity of the target galaxies - that is, how fast galaxies seem to be moving away. The team's calculations give a Hubble constant of 69.8 km/sec/Mpc - straddling the values derived by the Planck and Riess teams.

"Our initial thought was that if there's a problem to be resolved between the Cepheids and the Cosmic Microwave Background, then the red giant method can be the tie-breaker," said Freedman.

But the results do not appear to strongly favor one answer over the other say the researchers, although they align more closely with the Planck results.

NASA's upcoming mission, the Wide Field Infrared Survey Telescope (WFIRST), scheduled to launch in the mid-2020s, will enable astronomers to better explore the value of the Hubble constant across cosmic time. WFIRST, with its Hubble-like resolution and 100 times greater view of the sky, will provide a wealth of new Type Ia supernovae, Cepheid variables, and red giant stars to fundamentally improve distance measurements to galaxies near and far.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

Related:
Department members: Wendy L. Freedman, Barry Madore
Department students: Taylor Hoyt

Faculty who inspire students honored with UChicago teaching awards
June 6, 2019
Prof. Wayne Hu
Photo by Jean Lachat
Click on the image to enlarge
UChicago News
Wayne Hu, Horace B. Horton Professor in the Department of Astronomy and Astrophysics and the College

As Wayne Hu creates models for how the universe developed over time, he also takes pride in watching his graduate students develop and grow.

"My ultimate goal is to try to get them to think on their own," Hu said. "When you start a career, there can be quite a shock of doing things on your own. You have to show you can lead the project, not just carry out some project you're told to do. So I do as much as I can to prepare them for that moment."

Hu encourages independent thinking at every turn, giving students room to breathe on projects and having them run group meetings - inspired by his time as a postdoctoral researcher at the Institute for Advanced Study, which hosts weekly lunches in which every person in the department has to present his or her research.

Hu also urges students to collaborate with other professors in the department, and encourages them to branch out from the questions they study in his group.

His favorite part of teaching, he said, "is when the student starts telling me things I don't know. Each one has their own moment like that. That's when I know they're really ready."

Related:
Department members: Wayne Hu

Astronomers May Have Detected Neutron Star Being Consumed by Black Hole
May 15, 2019
Click on the image to enlarge
WWCI, by Paul Caine
Astronomers in the U.S. and Italy believe they may have detected gravitational waves created when a black hole swallowed a neutron star. If the discovery is confirmed, it would be the first evidence that black holes and neutron stars can pair up to form binary systems.

The apparent detection was made on April 26 by the twin LIGO observatories in the U.S. and the Virgo detector in Italy.

Neutron stars are extremely dense stars formed when massive stars collapse.

"A neutron star is kind of the most extreme star that is possible," said Daniel Holz, a University of Chicago astrophysicist who is part of the LIGO team. "When a star starts collapsing the first stop along the way is a white dwarf and that's when electrons inside the star are pushing against each other and that can hold the star up. But if the star is big enough it will continue to collapse and you'd end up with something called a neutron star. And that's when the neutrons are actually pushing against each other. And as far as we know that is it, that's the densest matter that is possible."

Related:
Department members: Daniel E. Holz
Scientific projects: Laser Interferometer Gravitational-wave Observatory

Astronomers Take First-Ever Picture of a Black Hole
April 11, 2019
Click on the image to enlarge
Chicago Tonight (WTTW), by Paul Caine
An international team of astronomers has for the very first time captured an image of one of the most exotic and mysterious objects in the universe: a black hole.

Ever since Einstein's theory of relativity first predicted them, black holes have captured the imagination of the public and scientists alike.

A black hole is an object so dense, literally so massive, that the gravity it generates is so strong that light itself cannot escape and even the fabric of space-time breaks down.

"Black holes are one of those things where the public fascination and the scientific fascination completely align," said Daniel Holz, an astrophysicist at the University of Chicago and part of the LIGO team that in 2016 first detected gravitational waves from the collision of two black holes.

"From a scientific perspective they are also incredibly extreme. The equations are very clean. You end up with this solution. But the solution is so crazy - the idea that there are black holes - that even Einstein said they are probably not real," said Holz.

But real they are and now we have a picture of one.

Carlstrom said that his first reaction on seeing the image of the black hole for the first time was: "Holy Smokes! It really works."

"For the people who have worked in this field for decades it's just disbelief that it is really there," he added.

Related:
Department members: John E. Carlstrom, Daniel E. Holz
Scientific projects: Laser Interferometer Gravitational-wave Observatory, South Pole Telescope

Astronomers capture historic first image of a black hole
April 10, 2019
The first image ever captured of a black hole.
Courtesy of EHT Collaboration
Click on the image to enlarge
UChicago News
South Pole Telescope contributes to observations of black hole in distant galaxy

The Event Horizon Telescope - a planet-scale array of eight ground-based radio telescopes forged through international collaboration - was designed to capture images of a black hole. On April 10, in coordinated news conferences across the globe, researchers reveal that they have succeeded, unveiling the first direct visual evidence of a supermassive black hole and its shadow.

This breakthrough was announced April 10 in a series of six papers published in a special issue of The Astrophysical Journal Letters. The image reveals the black hole at the center of Messier 87, a massive galaxy in the nearby Virgo galaxy cluster. This black hole sits 55 million light-years from Earth and has a mass 6.5 billion times that of the sun.

The EHT links telescopes around the globe, including the University of Chicago-run South Pole Telescope, to form an unprecedented Earth-sized "virtual telescope" with unprecedented sensitivity and resolution. The EHT is the result of years of international collaboration, and offers scientists a new way to study the most extreme objects in the universe predicted by Einstein's theory of general relativity.

"The South Pole Telescope's location at the southernmost point of the Earth makes it an important component of the global EHT network," said Prof. John Carlstrom, who directs the telescope. "Although M87 is not visible from the South Pole, it is a crucial player in observing other black holes, such as the massive one at the center of our own galaxy."

Related:
Department members: John E. Carlstrom
Scientific projects: South Pole Telescope

How to use gravitational waves to measure the expansion of the universe
April 2, 2019
Prof. Daniel Holz
University of Chicago News Office, by Louise Lerner
Prof. Daniel Holz discusses a new way to calculate the Hubble constant, a crucial number that measures the expansion rate of the universe and holds answers to questions about the universe's size, age and history.

Related:
Department members: Daniel E. Holz
Scientific projects: Laser Interferometer Gravitational-wave Observatory

Lifetime Achievement Award
March 13, 2019
Wendy L. Freedman, John and Marion Sullivan University Professor in Astronomy and Astrophysics, University of Chicago
Click on the image to enlarge
The Chicago Council on Science and Technology
Wendy Freedman is a renowned astronomer who was instrumental in precisely measuring the Hubble constant and determining the age of the universe. Freedman received both her BSc and PhD in astronomy and astrophysics from the University of Toronto. In 1984 she accepted a position as a postdoctoral fellow at the Carnegie Observatories in Pasadena, California. In 1987 Freedman became the first woman to join Carnegie's permanent staff, and in 2003 she became its director. She also initiated the Giant Magellan Telescope project and served as chair of its board of directors from the project's inception in 2003 until 2015. In 2014 she joined the faculty of the University of Chicago as the John and Marion Sullivan University Professor of Astronomy and Astrophysics. Freedman first rose to prominence leading the Hubble Space Telescope Key Project, which began in the mid-1980s and involved an international group of some 30 astronomers. The team used the Hubble telescope to study Cepheid variable stars in order to estimate intergalactic distances and thus determine the expansion rate of the universe.

Related:
Department members: Wendy L. Freedman
Scientific projects: Giant Magellan Telescope

Edward 'Rocky' Kolb to direct Kavli Institute for Cosmological Physics
February 27, 2019
Prof. Rocky Kolb
Photo by Jason Smith
UChicago News
Cosmologist to lead center dedicated to study of origin and evolution of universe

The University of Chicago has named Edward W. 'Rocky' Kolb as director of its Kavli Institute for Cosmological Physics, a leading center dedicated to deepening our understanding of the origin and evolution of the universe and the laws that govern it.

Kolb, the Arthur Holly Compton Distinguished Service Professor in the Department of Astronomy and Astrophysics, succeeds Michael S. Turner as director, effective April 1. Turner, the Bruce V. & Diana M. Rauner Distinguished Service Professor in the Department of Astronomy and Astrophysics, has served in the role since 2010.

"We are thrilled that Rocky Kolb will lead KICP. Kolb, together with current KICP director Michael Turner, helped define a new discipline at the intersection of cosmology, particle physics and astrophysics," said Angela V. Olinto, dean of the Physical Sciences Division. "Kolb's extensive leadership experience will guarantee a brilliant future for KICP."

The institute was created as an interdisciplinary center to bridge astronomy and physics, exploring physics ranging from the subatomic scale to the birth and constitution of the cosmos. It is an international hub for cosmology and has furthered the careers of many young scientists.

At the institute, UChicago researchers tackle questions about the nature of dark energy and dark matter, the first moments of the universe, and nature's highest-energy particles. Members lead some of the most significant international astronomy projects in the field, such as the Dark Energy Survey, an unprecedented survey of distant galaxies to better understand the mysterious force accelerating the expansion of the universe; the South Pole Telescope, which with its third-generation camera will be among the most sensitive instruments observing the cosmic microwave background; and the Giant Magellan Telescope, a giant ground-based telescope under construction in Chile that is expected to produce images that are 10 times sharper than those from the Hubble Space Telescope.

"Rocky Kolb is an eminent cosmologist, known for his contributions to the study of the very early universe," said Kevin Moses, vice president of science programs at the Kavli Foundation. "He has had a distinguished career at the University of Chicago and Fermi National Accelerator Laboratory and is a longtime member of KICP. Rocky will continue the strong tradition of leadership at KICP, paving the way for further understanding of our cosmos."

Kolb is a fellow of the American Academy of Arts and Sciences and the American Physical Society. He has received numerous honors, including the Dannie Heineman Prize for Astrophysics, which he shared with Turner for their work to understand the early universe. Kolb has formerly served as dean of the Physical Sciences Division, chair of the Department of Astronomy and Astrophysics, and director of Fermi National Accelerator Laboratory's Particle Astrophysics Center.

The University established the Center for Cosmological Physics in 2001 with National Science Foundation support. The center was renamed the Kavli Institute for Cosmological Physics in 2004 in honor of Fred Kavli, who through the Kavli Foundation provided $7.5 million to endow the institute and support its programs.

UChicago's Kavli Institute works closely with the other Kavli Institutes in astrophysics at Stanford University, Peking University, Massachusetts Institute of Technology, University of California, Berkeley; and the University of Cambridge.

Related:
Department members: Edward ''Rocky'' W. Kolb, Angela V. Olinto, Michael S. Turner
Scientific projects: Dark Energy Survey, Giant Magellan Telescope

Big Brains podcast: "What Ripples in Space-Time Tell Us About the Universe with Daniel Holz"
January 24, 2019
Prof. Daniel Holz
Click on the image to enlarge
UChicago News
UChicago cosmologist discusses discovery of gravitational waves and colliding black holes

All around us in the universe, black holes are smashing into each other with tremendous force. These events are so powerful that they cause ripples in the fabric of space-time - and these ripples, called gravitational waves, travel hundreds of millions of light-years across the universe, eventually passing through the Earth.

Prof. Daniel Holz and fellow scientists at LIGO knew that detecting these waves would take us closer to figuring out many profound mysteries, including the size, age and composition of the universe. They built the most sensitive machine ever constructed, detected the waves and opened up an entirely new window on the universe.

In this time-and-space-bending episode of Big Brains, the UChicago cosmologist talks black holes, testing Einstein's predictions, and the threat of nuclear annihilation.

Related:
Department members: Daniel E. Holz
Scientific projects: Laser Interferometer Gravitational-wave Observatory

After mapping millions of galaxies, Dark Energy Survey finishes data collection
January 15, 2019
UChicago News
For the past six years, Fermi National Accelerator Laboratory has been part of an international effort to create an unprecedented survey of distant galaxies and better understand the nature of dark energy - the mysterious force accelerating the expansion of the universe.

After scanning about a quarter of the southern skies over 800 nights, the Dark Energy Survey finished taking data on Jan. 9. It ends as one of the most sensitive and comprehensive surveys of its kind, recording data from more than 300 million distant galaxies.

Fermilab, an affiliate of the University of Chicago, served as lead laboratory on the survey, which included more than 400 scientists and 26 institutions. The findings created the most accurate dark matter map of the universe ever made, shaping our understanding of the cosmos and its evolution. Other discoveries include the most distant supernova ever detected, a bevy of dwarf satellite galaxies orbiting our Milky Way, and helping to track the first-ever detection of gravitational waves from neutron stars back to its source.

According to Dark Energy Survey Director Rich Kron, a Fermilab scientist and professor at the University of Chicago, those results - and the scientists who made them possible - are where much of the real accomplishment of the Dark Energy Survey lies.

"The first generations of students and postdoctoral researchers on the Dark Energy Survey are now becoming faculty at research institutions and are involved in upcoming sky surveys," Kron said. "The number of publications and people involved are a true testament to this experiment. Helping to launch so many careers has always been part of the plan, and it's been very successful."

Now the job of analyzing that data takes center stage, providing opportunities for new breakthroughs. The survey has already released a full range of papers based on its first year of data, and scientists are now diving into the rich seam of catalogued images from the first several years of data, looking for clues to the nature of dark energy.

The first step in that process, according to Fermilab scientist Josh Frieman, a professor at UChicago and former director of the Dark Energy Survey, is to find the signal in all the noise.

"We're trying to tease out the signal of dark energy against a background of all sorts of non-cosmological stuff that gets imprinted on the data,' Frieman said. "It's a massive ongoing effort from many different people around the world."

Related:
Department members: Joshua A. Frieman, Richard G. Kron
Scientific projects: Dark Energy Survey

Distortion
December 1, 2018
Brian Nord, visiting research assistant professor in the UChicago Department of Astronomy and Astrophysics
University of Chicago Magazine, by Brian Nord, Maureen Searcy
Astrophysicist Brian Nord looks for lenses through AI eyes.

Brian Nord is a visiting research assistant professor in the UChicago Department of Astronomy and Astrophysics, an associate scientist in the Machine Intelligence Group at Fermilab, and a senior member of the Kavli Institute for Cosmological Physics. He is a leader in the institute's Space Explorers educational program for high school students and a cofounder of Deep Skies, a collaborative research group that applies artificial intelligence to astrophysics.

Related:
Department members: Brian Nord

Studying the stars with machine learning
November 12, 2018
Click on the image to enlarge
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.

Related:
Department members: Brian Nord

Flash Center turns 20, welcomes new director
October 29, 2018
Petros Tzeferacos, new director of the Flash Center for Computational Science
PSD News
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."

Related:
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.

Related:
Department members: Daniel E. Holz
Department students: Maya Fishbach
Scientific projects: Laser Interferometer Gravitational-wave Observatory