Department in the News
Researchers Provide New Insight Into Dark Matter Halos
April 19, 2017
University of Pennsylvania
Many scientists now believe that more than 80 percent of the matter of the universe is locked away in mysterious, as yet undetected, particles of dark matter, which affect everything from how objects move within a galaxy to how galaxies and galaxy clusters clump together in the first place.
This dark matter extends far beyond the reach of the furthest stars in the galaxy, forming what scientists call a dark matter halo. While stars within the galaxy all rotate in a neat, organized disk, these dark matter particles are like a swarm of bees, moving chaotically in random directions, which keeps them puffed up to balance the inward pull of gravity.
Bhuvnesh Jain, a physics professor in Penn's School of Arts & Sciences, and postdoc Eric Baxter are conducting research that could give new insights into the structure of these halos.
The researchers wanted to investigate whether these dark matter halos have an edge or boundary.
"People have generally imagined a pretty smooth transition from the matter bound to the galaxy to the matter between galaxies, which is also gravitationally attracted to the galaxies and clusters," Jain said. "But theoretically, using computer simulations a few years ago, researchers at the University of Chicago showed that for galaxy clusters a sharp boundary is expected, providing a distinct transition that we should be able to see through a careful analysis of the data."
Using a galaxy survey called the Sloan Digital Sky Survey, or SDSS, Baxter and Jain looked at the distribution of galaxies around clusters. They formed a team of experts at the University of Chicago and other institutions around the world to examine thousands of galaxy clusters. Using statistical tools to do a joint analysis of several million galaxies around them, they found a drop at the edge of the cluster. Baxter and collaborator Chihway Chang at the University of Chicago led a paper reporting the findings, accepted for publication in the Astrophysical Journal.
Department members: Andrey V. Kravtsov
Prof. Angela Olinto leads project to collect data at near-space altitudes
April 6, 2017
UChicago News, by Greg Borzo
NASA to launch telescope on super-pressure balloon in search for cosmic rays
The National Aeronautics and Space Administration is preparing to use a super-pressure balloon to launch into near space a pioneering telescope designed to detect ultra-high-energy cosmic rays as they interact with the Earth's atmosphere.
"We're searching for the most energetic cosmic particles that we've ever observed," said Angela V. Olinto, the Homer J. Livingston Distinguished Service Professor at the University of Chicago and principal investigator of the project, known as the Extreme Universe Space Observatory-Super Pressure Balloon. "The origin of these particles is a great mystery that we'd like to solve. Do they come from massive black holes at the center of galaxies? Tiny, fast-spinning stars? Or somewhere else?"
The extremely rare particles hit the atmosphere at a rate of only one per square kilometer per century. To assure that it will capture some of the particles, the telescope's camera takes 400,000 images a second as it casts a wide view back toward the Earth.
Preparations are complete in Wanaka, New Zealand for the balloon's launch, which will happen as soon as scientists and engineers have the right weather conditions. Researchers hope the balloon will stay afloat for up to 100 days, thereby setting a record for an ultra-long duration flight.
NASA describes the super-pressure balloon as the "most persnickety" of all the flight and launch vehicles it operates. Launching the balloon depends on just the right weather conditions on the surface of the Earth all the way up to 110,000 feet, where the balloon travels.
The project will set the stage for a space mission currently being planned. "That would enlarge even more the volume of the atmosphere that we can observe at one time," said Olinto, who serves as chair of UChicago's Department of Astronomy and Astrophysics. "We need to observe a significantly large number of these cosmic messengers to discover what are their sources and how they interact at their energetic extremes."
When an ultra-high-energy cosmic ray reaches the Earth's atmosphere, it induces a series of interactions that stimulates a large cosmic ray shower. The new telescope, which detects at night, will capture the ultra-violet fluorescence produced by the interaction of these particle showers with the nitrogen molecules in the air.
"High-energy cosmic rays have never been observed this way from space," said Lawrence Wiencke, professor of physics at the Colorado School of Mines and co-leader of the project. "This mission to a sub-orbital altitude is a pioneering opportunity for us. Our international collaboration is very excited about this launch and about the new data that will be collected along the way."
The project lends itself to participation by graduate and undergraduate students, Olinto said. Leo Allen and Mikhail Rezazadeh, two UChicago undergraduates, built an infrared camera under the supervision of UChicago Prof. Stephan Meyer and Olinto to observe the cloud coverage at night under EUSO-SPB.
Sixteen countries were involved with the design of the telescope. The U.S. team, funded by NASA, is led by UChicago, Colorado School of Mines, Marshall Space Flight Center, University of Alabama at Huntsville and Lehman College at the City University of New York.
Department members: Stephan S. Meyer, Angela V. Olinto
Scientific projects: Extreme Universe Space Observatory at the Japanese Module
A recharged debate over the speed of the expansion of the universe could lead to new physics
March 9, 2017
AAAS, by Joshua Sokol
It was the early 1990s, and the Carnegie Observatories in Pasadena, California, had emptied out for the Christmas holiday. Wendy Freedman was toiling alone in the library on an immense and thorny problem: the expansion rate of the universe.
Carnegie was hallowed ground for this sort of work. It was here, in 1929, that Edwin Hubble first clocked faraway galaxies flying away from the Milky Way, bobbing in the outward current of expanding space. The speed of that flow came to be called the Hubble constant.
Freedman's quiet work was soon interrupted when fellow Carnegie astronomer Allan Sandage stormed in. Sandage, Hubble's designated scientific heir, had spent decades refining the Hubble constant, and had consistently defended a slow rate of expansion. Freedman was the latest challenger to publish a faster rate, and Sandage had seen the heretical study.
"He was so angry," recalls Freedman, now at the University of Chicago in Illinois, "that you sort of become aware that you're the only two people in the building. I took a step back, and that was when I realized, oh boy, this was not the friendliest of fields."
The acrimony has diminished, but not by much. Sandage died in 2010, and by then most astronomers had converged on a Hubble constant in a narrow range. But in a twist Sandage himself might savor, new techniques suggest that the Hubble constant is 8% lower than a leading number. For nearly a century, astronomers have calculated it by meticulously measuring distances in the nearby universe and moving ever farther out. But lately, astrophysicists have measured the constant from the outside in, based on maps of the cosmic microwave background (CMB), the dappled afterglow of the big bang that is a backdrop to the rest of the visible universe. By making assumptions about how the push and pull of energy and matter in the universe have changed the rate of cosmic expansion since the microwave background was formed, the astrophysicists can take their map and adjust the Hubble constant to the present-day, local universe. The numbers should match. But they don't.
It could be that one approach has it wrong. The two sides are searching for flaws in their own methods and each other's alike, and senior figures like Freedman are racing to publish their own measures. "We don't know which way this is going to land," Freedman says.
Department members: Wendy L. Freedman
Kumiko Kotera: doing beautiful physics without giving up on family, art and the rest of the world
February 24, 2017
e-EPS, by Lucia Di Ciaccio
Kumiko Kotera is a young researcher in Astrophysics, at the Institut d'Astrophysique de Paris, (IAP) of the French Centre National de la Recherche Scientifique (CNRS). She builds theoretical models to probe the most violent phenomena in the Universe, by deciphering their so-called "astroparticle" messengers (cosmic rays, neutrinos and photons). Today, she is one of the leaders of the international project GRAND (Giant Radio Array for Neutrino Detection), that aims at detecting very-high energy cosmic neutrinos. In 2016, she received a prestigious award: the CNRS bronze medal for her important achievements.
Lucia Di Ciaccio: Do you have any female 'physicist cult figure' or 'role model'?
Kumiko Kotera: Angela Olinto, professor at the University of Chicago, is undoubtedly my mentor. She struggled to build her brilliant career at a time when female physicists were far more isolated than today and opened the path for all of us. She showed me how one can be strong, respected, and do beautiful physics without ever giving up on kindness, family, art, and the rest of the world.
Department members: Angela V. Olinto
Cosmos Controversy: The Universe Is Expanding, but How Fast?
February 21, 2017
The New York Times, by Dennis Overbye
A small discrepancy in the value of a long-sought number has fostered a debate about just how well we know the cosmos.
There is a crisis brewing in the cosmos, or perhaps in the community of cosmologists. The universe seems to be expanding too fast, some astronomers say. Recent measurements of the distances and velocities of faraway galaxies don't agree with a hard-won "standard model" of the cosmos that has prevailed for the past two decades. The latest result shows a 9 percent discrepancy in the value of a long-sought number called the Hubble constant, which describes how fast the universe is expanding. But in a measure of how precise cosmologists think their science has become, this small mismatch has fostered a debate about just how well we know the cosmos. "If it is real, we will learn new physics," said Wendy Freedman of the University of Chicago, who has spent most of her career charting the size and growth of the universe.
Michael S. Turner of the University of Chicago said, "If the discrepancy is real, this could be a disruption of the current highly successful standard model of cosmology and just what the younger generation wants - a chance for big discoveries, new insights and breakthroughs."
Department members: Wendy L. Freedman, Michael S. Turner
Galactic X-rays could point to dark matter proof
February 2, 2017
BBC News, by Edwin Cartlidge
Prof. Dan Hooper discusses a recent claim of the detection of the 3.5 keV X-ray line in our Galaxy with the BBC.
"The new paper claims a modest detection," said Dr Hooper, "but it doesn't sway me very strongly at this point."
Department members: Dan Hooper
U of C Astronomers Discover "Twin Star," Develop Insight Into Planetary Movement
January 14, 2017
The Chicago Maroon, by Stephanie Palazzolo
University of Chicago researchers have discovered a planetary system based around "solar twin" HIP68468, a star that shares many similarities with the Sun.
Unlike the Sun, this star contains abnormal amounts of lithium, levels that would be more common in a much younger star, as lithium gets consumed by a star during its lifetime.
"Lithium is like the 'smoking gun' evidence in this case that there's something unusual about this star," said Megan Bedell, a UChicago graduate student and leader of the planet search portion of this project. "[It's] kind of an unusual element in that it actually gets consumed by the star during the course of its lifetime, so as [the star] grows older, the lithium gets eaten up in the same process that fuses the hydrogen to create energy in the star."
High levels of lithium in HIP68468, which usually indicates a young star, contradicts its actual age -- 6 billion years compared to the Sun's 4.5 billion years.
"Planets have lithium, so we inferred that the extra lithium [is due to] planetary pollution on the outside of the star," Bedell said. "We also see that extra rocky material -- iron and things that make up the Earth -- tend up to be fairly prevalent in this star compared to other solar twin stars and the Sun, especially."
Therefore, Bedell's group, under the mentorship of her thesis adviser Jacob Bean, assistant professor of astronomy and astrophysics at the University of Chicago, and collaborating with a team of international scientists, including Brazilian scientist and lead author Jorge Melendez, came to the conclusion that star HIP68468 actually devoured nearby planets, which would explain the inconsistencies in the composition of the star.
Bedell's discovery of two nearby planets, a "super Earth" and a "super Neptune," also supports this hypothesis, as they seem to have migrated closer to the star over time.
"We can guess that the 'super Earth' formed somewhere close to where the Earth did [in our solar system] and the 'super Neptune' probably formed much further away," Bedell said. "In both cases today, we see them in a place where they're so close to the star and so hot that it just wouldn't have been possible for the material to condense in that place in the early solar system."
Bedell observed these planets with a Chile-based spectrograph called High Accuracy Radial Velocity Planet Searcher (HARPS). This instrument breaks down light from stars into the component colors, and researchers then use the spectrum it creates to find planets and discover the composition of stars.
"We have to keep using HARPS to observe the star many times over a period of years because you want to see the small changes that happen in the star during the time it takes for the planet to do an orbit around the star," Bedell said. "I've been going to Chile about three times a year or so for the past few years and using the same instrument to keep track of how the stars are changing through time. Using that, I can then find out whether or not they have planets and what the planets are like."
By looking at "solar twins" like HIP68468, researchers gain insight into the future of our own solar system.
"It's kind of cool to see what the planetary systems of these stars are like, especially if there's a lot of debate about how planet migration might happen over time -- maybe the system that's born around a young star doesn't stay stable like that, and it'll get rearranged over the star's lifetime," Bedell said. "So if you see a really old solar twin, maybe that's what the Sun will end up looking like."
In addition, looking at systems like the one surrounding star HIP68468 provides a "stepping stone" to questions about other Earth-like planets, Bedell said.
"[It's] got a lot of implications for the solar system and especially how common an Earth-like system is, whether other Earths out there are habitable or whether a lot of stars have this migration event that renders everything too hot to be inhabited," Bedell said. "It's nice evidence that we're on the right path for what the current theory is to explain these systems."
The group plans on continuing their research on the star system to verify their findings.
"We would like to keep taking measurements of the star's radial velocity to confirm the planet candidates that we identified and to search for additional planets," Bean said. "We also want to compare the star's unusual abundance pattern to that of other similar stars to determine how common this sort of phenomenon is."
However, even though solar twin HIP68468 might be engulfing nearby planets, Bedell dismisses fears about Earth being similarly destroyed by the Sun any time soon.
"I mean, if we're going to stick around for 5 billion years, we'll have to worry about the Sun devouring the Earth because eventually the Sun will swell up into a red giant, but I think this points to us being safe until the next phase of the Sun's life starts," Bedell said. "We're probably not going to go spiraling into the Sun at any moment."
Department members: Jacob L. Bean
Department students: Megan Bedell
Research reinforces role of supernovae in clocking the universe
January 4, 2017
UChicago News, by Greg Borzo
How much light does a supernova shed on the history of universe?
New research by cosmologists at the University of Chicago and Wayne State University confirms the accuracy of Type Ia supernovae in measuring the pace at which the universe expands. The findings support a widely held theory that the expansion of the universe is accelerating and such acceleration is attributable to a mysterious force known as dark energy. The findings counter recent headlines that Type Ia supernova cannot be relied upon to measure the expansion of the universe.
Using light from an exploding star as bright as entire galaxies to determine cosmic distances led to the 2011 Nobel Prize in physics. The method relies on the assumption that, like lightbulbs of a known wattage, all Type Ia supernovae are thought to have nearly the same maximum brightness when they explode. Such consistency allows them to be used as beacons to measure the heavens. The weaker the light, the farther away the star. But the method has been challenged in recent years because of findings the light given off by Type Ia supernovae appears more inconsistent than expected.
"The data that we examined are indeed holding up against these claims of the demise of Type Ia supernovae as a tool for measuring the universe," said Daniel Scolnic, a postdoctoral scholar at UChicago’s Kavli Institute for Cosmological Physics and co-author of the new research published in Monthly Notices of the Royal Astronomical Society. "We should not be persuaded by these other claims just because they got a lot of attention, though it is important to continue to question and strengthen our fundamental assumptions."
One of the latest criticisms of Type Ia supernovae for measurement concluded the brightness of these supernovae seems to be in two different subclasses, which could lead to problems when trying to measure distances. In the new research led by David Cinabro, a professor at Wayne State, Scolnic, Rick Kessler, a senior researcher at the Kavli Institute, and others, they did not find evidence of two subclasses of Type Ia supernovae in data examined from the Sloan Digital Sky Survey Supernovae Search and Supernova Legacy Survey. The recent papers challenging the effectiveness of Type Ia supernovae for measurement used different data sets.
A secondary criticism has focused on the way Type Ia supernovae are analyzed. When scientists found that distant Type Ia supernovae were fainter than expected, they concluded the universe is expanding at an accelerating rate. That acceleration is explained through dark energy, which scientists estimate makes up 70 percent of the universe. The enigmatic force pulls matter apart, keeping gravity from slowing down the expansion of the universe.
Yet a substance that makes up 70 percent of the universe but remains unknown is frustrating to a number of cosmologists. The result was a reevaluation of the mathematical tools used to analyze supernovae that gained attention in 2015 by arguing that Type Ia supernovae don't even show dark energy exists in the first place.
Scolnic and colleague Adam Riess, who won the 2011 Nobel Prices for the discovery of the accelerating universe, wrote an article for Scientific American Oct. 26, 2016, refuting the claims. They showed that even if the mathematical tools to analyze Type Ia supernovae are used "incorrectly," there is still a 99.7 percent chance the universe is accelerating.
The new findings are reassuring for researchers who use Type Ia supernovae to gain an increasingly precise understanding of dark energy, said Joshua A. Frieman, senior staff member at the Fermi National Accelerator Laboratory who was not involved in the research.
"The impact of this work will be to strengthen our confidence in using Type Ia supernovae as cosmological probes," he said.
Department members: Joshua A. Frieman, Richard Kessler
Scientific projects: Sloan Digital Sky Survey
Astronomers discover dark past of planet-eating 'Death Star'
December 15, 2016
UChicago News, by Greg Borzo
Solar twin could hold clues to planetary formation
An international team of scientists, including researchers from the University of Chicago, has made the rare discovery of a planetary system with a host star similar to Earth's sun. Especially intriguing is the star's unusual composition, which indicates it ingested some of its planets.
"It doesn't mean that the sun will 'eat' the Earth any time soon," said Jacob Bean, assistant professor of astronomy and astrophysics at UChicago and co-author of an Astronomy & Astrophysics article on the research. "But our discovery provides an indication that violent histories may be common for planetary systems, including our own."
Unlike the artificial planet-destroying Death Star in the movie "Star Wars," this natural version could provide clues about how planetary systems evolve over time.
Astronomers discovered the first planet orbiting a star other than the sun in 1995. Since then, more than two thousand exoplanets have been identified. Rare among them are planets that orbit a star similar to Earth's sun. Due to their extreme similarity to the sun, these so-called solar twins are ideal targets for investigating the connections between stars and their planets.
Bean and his colleagues studied star HIP68468, which is 300 light years away, as part of a multi-year project to discover planets that orbit solar twins. It's tricky to draw conclusions from a single system, cautioned Megan Bedell, a UChicago doctoral student who is co-author of the research and the lead planet finder for the collaboration. She said the team plans "to study more stars like this to see whether this is a common outcome of the planet formation process."
Department members: Jacob L. Bean
Department students: Megan Bedell
Daniel Holz: Gravitational Waves
October 13, 2016
The Good Stuff
In 2015 scientists working at the Laser Interferometer Gravitational-Wave observatory, or LIGO, detected gravitational waves for the first time. But how did they do it? What is a gravitational wave? And why is confirming something that Albert Einstein predicted a hundred years ago one of the greatest scientific achievements of the past century?
Department members: Daniel E. Holz
Department students: Hsin-Yu Chen, Zoheyr Doctor
Why is this star dimming? Astronomers still don't know
October 6, 2016
Fox News Science, by Rob Verger
A strange star in our galaxy has officially become even more enigmatic: According to data collected by NASA's Kepler space telescope, the star mysteriously dimmed over a period of a few years.
The star is called KIC 8462852, and it was already on scientists' radar for fluctuations in its brightness. So two astronomers decided to study it more carefully, using images from Kepler. They discovered that from 2009 to 2012, the star's brightness declined by just under 1 percent. Then, over a time period of six months, its brightness plunged by 2 percent. While news of their discovery first surfaced in August, their work has now been accepted for publication in an astronomy journal, the Carnegie Institution for Science announced on Monday.
"The steady brightness change in KIC 8462852 is pretty astounding," Ben Montet, an astronomer and fellow at the University of Chicago, said in a statement. "Our highly accurate measurements over four years demonstrate that the star really is getting fainter with time. It is unprecedented for this type of star to slowly fade for years, and we don't see anything else like it in the Kepler data."
Montet is coauthor on the new study about the star, forthcoming in the Astrophysical Journal.
Department members: Benjamin Montet
Physics Confronts Its Heart of Darkness
September 1, 2016
Scientific American, by Lee Billings
Cracks are showing in the dominant explanation for dark matter. Is there anything more plausible to replace it?
Physics has missed a long-scheduled appointment with its future - again. The latest, most sensitive searches for the particles thought to make up dark matter - the invisible stuff that may comprise 85 percent of the mass in the cosmos - have found nothing. Called WIMPs (weakly interacting massive particles), these subatomic shrinking violets may simply be better at hiding than physicists thought when they first predicted them more than 30 years ago. Alternatively, they may not exist, which would mean that something is woefully amiss in the underpinnings of how we try to make sense of the universe. Many scientists still hold out hope that upgraded versions of the experiments looking for WIMPs will find them but others are taking a second look at conceptions of dark matter long deemed unlikely.
Whatever dark matter is, it is not accounted for in the Standard Model of particle physics, a thoroughly-tested "theory of almost everything" forged in the 1970s that explains all known particles and all known forces other than gravity. Find the identity of dark matter and you illuminate a new path forward to a deeper understanding of the universe - at least, that is what physicists hope.
WIMPs would get their gravitational heft from being somewhere between one and a thousand times the mass of a proton. Their sole remaining connection to our familiar world would be through the weak nuclear force, which is stronger than gravity but only active across tiny distances on the scale of atomic nuclei. If they exist, WIMPs should surround us like an invisible fog, their chances of interacting with ordinary matter so remote that one could pass through light-years of elemental lead unscathed.
Undaunted, experimentalists have spent decades devising and operating enough cleverly named WIMP detectors to overflow your average can of alphabet soup. (CDEX, CDMS, CoGeNT, COUPP and CRESST are just the most notable examples that start with the letter C.) The delicate work of detecting any weak, rare and fleeting interactions of WIMPs with atoms requires isolation and solitude, confining most detectors to caverns, abandoned mines and other outlier subterranean spaces.
One of the latest null results in the search for WIMPs came from the Large Underground Xenon (LUX) experiment, a third of a ton of liquid xenon held at a frosty -100 degrees Celsius inside a giant water-filled tank buried one and a half kilometers beneath the Black Hills of South Dakota. There, shielded from most sources of contaminating noise, researchers have spent more than a year's worth of time looking for flashes of light emanating from WIMPs striking xenon nuclei. On July 21 they announced they had seen none.
The next disappointment came on August 5 from the most powerful particle accelerator ever built: CERN's Large Hadron Collider (LHC) near Geneva, Switzerland. In 2012 after it found the Higgs boson - the Standard Modelâ€™s long-predicted final particle that imbues others with mass - many theorists believed the next blockbuster result from the LHC would be a discovery of how the Higgs (or other hypothesized particles very much like it) helps produce the WIMPs thought to suffuse the cosmos. Since spring 2015 the LHC has been pursuing these ideas by smashing protons together at unprecedentedly high energies at rates of up to a billion per second, pushing into new frontiers of particle physics. Early on, two independent teams had spied a telltale anomaly in the subatomic wreckage, an excess of energy from proton collisions that hinted at new physics perhaps produced by WIMPs (or, to be fair, many additional exotic possibilities). Instead, as the LHC smashed more protons and collected more data, the anomaly fizzled out, indicating it had been a statistical fluke.
Taken together, these two null results are a double-edged sword for dark matter. On one hand, their new constraints on the plausible masses and interactions of WIMPs are priming plans for next-generation detectors that could offer better chances of success. On the other, they have ruled out some of the simplest and most cherished WIMP models, raising fresh fears that the long-postulated particles might be a multidecadal detour in the search for dark matter.
Edward "Rocky" Kolb, a cosmologist now at the University of Chicago who in the 1970s helped lay the foundations for the generations of WIMP hunts to come, declared the 2010s "the decade of the WIMP" but now admits the search has not gone as planned. "We are now more in the dark about dark matter than we were five years ago," he says. So far, Kolb says, most theorists have responded by "letting a thousand WIMPs bloom," creating ever-more baroque and exotic theories to explain how WIMPs have managed to dodge all our detectors.
There is, of course, another possibility - that WIMPs are not the solution to dark matter we should be looking for. "WIMPs emerged as a simple, elegant, compelling explanation for a complex phenomenon," Kolb says. "And for every complex phenomenon there is a simple, elegant, compelling explanation that is wrong."
Department members: Edward ''Rocky'' W. Kolb
James W. Cronin, Nobel laureate and pioneering physicist, 1931-2016
August 27, 2016
UChicago News, by Steve Koppes
Scholar remembered for groundbreaking research on particle physics and cosmic rays
James W. Cronin, a pioneering scientist who shared the Nobel Prize in physics in 1980 for his groundbreaking work on the laws governing matter and antimatter and their role in the universe, died Aug. 25 in Saint Paul, Minn. He was 84.
Cronin, SM'53, PhD'55, spent much of his career at the University of Chicago, first as a student and then a professor. A University Professor Emeritus of Physics and Astronomy & Astrophysics, he was remembered this week as a mentor, collaborator and visionary.
"He inspired us all to reach further into the unknown with deep intuition, solid scientific backing and poetic vision," said Angela Olinto, the Homer J. Livingston Distinguished Service Professor in Astronomy and Astrophysics. "He accepted his many recognitions and accolades with so much humility that he encouraged many generations to follow his vision."
Edward "Rocky" Kolb, dean of the Physical Sciences Division and the Arthur Holly Compton Distinguished Service Professor in Astronomy and Astrophysics, described Cronin as â€śa person of real honesty and integrity who was a mentor and friend to so many people."
"Just like in basketball, there are good players in science, but the greatest players are the ones who make the people around them better. Jim was that great player," Kolb said.
Croninâ€™s research that resulted in the Nobel Prize came in 1964 while he was working with Val Fitch at the Brookhaven National Laboratory. The two scientists, who were Princeton University professors at the time, observed the first example of nature's preference for matter over antimatter. Without the phenomenon, which physicists refer to as charge-parity violation, no matter would exist in the universe.
Cronin and Fitch studied the short-lived subatomic particles that appeared after the collision of accelerated protons and the nucleus of an atom. They observed indirect charge-parity violation, which is the unbalanced mixing of neutral subatomic kaon particles with their charged antiparticles. Called the Fitch-Cronin effect, the finding showed that some physical laws are violated when the direction of time is reversed. It also lent support for the big bang theory of the universe's origin.
Cronin later in his career shifted his focus, becoming co-leader of the Pierre Auger Project. The $50 million international collaboration of 250 scientists across 16 nations focused on the mysterious sources of rare but extremely powerful cosmic rays that periodically bombard Earth. The project led to the creation of the Auger Observatory, which consists of a vast array of cosmic-ray detectors in Argentina.
"It was 25 years ago since Jim and I first conceived the idea of what became the Auger Collaboration. It was definitely a great partnership as we drummed up financial and scientific support for the collaboration," said Alan Watson, emeritus professor of physics at the University of Leeds and a fellow of the Royal Society.
The collaboration has made definitive measurements on the energy spectrum of cosmic rays, on the patterns of their arrival directions, and on their mass compositions. It also has conducted particle physics research, measuring phenomena that far exceed the energies of the Large Hadron Collider.
"It's been an outstanding success, and it's still going strong," Watson said.
Drawing inspiration from Fermi
Cronin was born on Sept. 29, 1931, in Chicago, while his father was a graduate student in classical languages and literatures at the University of Chicago. The younger Cronin received a bachelor's from Southern Methodist University in 1951 before returning to the University of Chicago as a National Science Foundation Fellow to earn his master's and doctoral degrees.
Cronin met his first wife, Annette Martin, while both were students at the University. She died in 2005, and Cronin married Carol McDonald (nee Champlin) in late 2006.
Cronin began his scientific career at Brookhaven before becoming a member of the physics faculty at Princeton in 1958. In 1971, he joined the University of Chicago, where he was appointed the University Professor of Physics. He became University Professor Emeritus of Physics and Astronomy & Astrophysics in 1997.
Cronin shared a birthdate with Prof. Enrico Fermi, who earned the Nobel Prize in Physics in 1938. Cronin, who knew Fermi from his graduate school days at UChicago, organized a symposium in 2001 to mark the 100th anniversary of Fermi's birth, and was editor of the resulting book, Fermi Remembered. It included contributions from seven Nobel Prize recipients and many other scientists who studied under or worked with Fermi at UChicago.
"What's significant about Fermi is if you look through his career, he never just did the same thing. He kept moving on to new scientific challenges," Cronin once said of Fermi. The same statement also could be applied to Cronin and his research shift from high-energy physics to ultra-high-energy cosmic rays.
Cronin's honors include the University of Chicago Alumni Medal (2013), election as a foreign member of the Royal Society of London (2007), Distinguished Graduate Award of SMU's Dedman College (2004), Legion dâ€™honneur of France (2001), National Medal of Science (1999), University of Chicago's Quantrell Award for Excellence in Undergraduate Teaching (1994), Laureate of Lincoln Academy of Illinois (1981), Ernest Lawrence Memorial Award for outstanding contributions in the field of atomic energy (1977), John Price Wetherill Medal of the Franklin Institute (1975) and the Research Corporation Award (1968).
In 1990 Cronin delivered the Ryerson Lecture, which provides an opportunity each year for a distinguished faculty member to address the UChicago community on significant aspects of his or her research.
He was a member of the National Academy of Sciences, American Academy of Arts and Sciences, American Physical Society, American Philosophical Society, Accademia Nazionale dei Lincei of Italy, Mexican Academy of Sciences and the Russian Academy of Sciences. Cronin also had received honorary doctorates from l'Universite Pierre et Marie Curie, University of Leeds, Universite de Franche Conte, Novo Gorica Polytechnique of Slovenia, University of Nebraska, the University of Santiago de Compostela, the Colorado School of Mines, and the Karlsruhe Institute of Technology. Cronin served as international chair of the College de France in 1999-2000.
Cronin is survived by his wife, Carol; daughter, Emily Grothe; son, Daniel Cronin; and six grandchildren: James, Cathryn, Caroline, Meredith, Alex and Marlo. A daughter, Cathryn Cranston, died in 2011.
Department members: James W. Cronin, Edward ''Rocky'' W. Kolb, Angela V. Olinto
Scientific projects: Pierre Auger Observatory
Angela Olinto received distinguished service professorship
July 21, 2016
Faculty members recognized with named, distinguished service professorships
Ten faculty members have received named professorships or have been named distinguished service professors. Luc Anselin, John R. Birge, John List and Angela Olinto received distinguished service professorships; and Ethan Bueno de Mesquita, Michael Franklin, Christopher Kennedy, Jason Merchant, Haresh Sapra and Nir Uriel received named professorships.
Angela Olinto has been named the Homer J. Livingston Distinguished Service Professor in Astronomy & Astrophysics and the College.
Olinto has made important contributions to the physics of quark stars, inflationary theory, cosmic magnetic fields and particle astrophysics. Her research interests span theoretical astrophysics, particle and nuclear astrophysics, and cosmology. She has focused much of her recent work on understanding the origins of the highest-energy cosmic rays and neutrinos.
Olinto is an elected fellow of the American Association for the Advancement of Science for her distinguished contributions to the field of astrophysics, particularly exotic states of matter and extremely high-energy cosmic ray studies at the Pierre Auger Observatory in Argentina. She now leads the International collaboration of the Extreme Universe Space Observatory mission that will fly in a NASA super pressure balloon in 2017 and will be first to observe tracks of ultra-energy particles from above.
She also is a fellow of the American Physical Society and has received the Chaire dâ€™Excellence Award of the French Agence Nationale de Recherche. Olinto has received the Llewellyn John and Harriet Manchester Quantrell Award for Excellence in Undergraduate Teaching, as well as the Faculty Award for Excellence in Graduate Teaching and Mentoring.
Olinto joined the UChicago faculty in 1996.
Department members: Angela V. Olinto
Angela Olinto: the 114th Congress Hearing - Astronomy, Astrophysics, and Astrobiology
July 12, 2016
Committee on Science, Space and Technology, 114th Congress
Joint Space Subcommittee and Research and Technology Subcommittee Hearing - Astronomy, Astrophysics, and Astrobiology
Tuesday, July 12, 2016 - 10:00am
- Space Subcommittee Chairman Brian Babin (R-Texas)
- Research and Technology Subcommittee Chairwoman Barbara Comstock (R-Va.)
- Chairman Lamar Smith (R-Texas)
Department members: Angela V. Olinto
Simulations foresee hordes of colliding black holes in observatory's future
June 28, 2016
UChicago News, by Steve Koppes
New calculations predict that the Laser Interferometer Gravitational wave Observatory (LIGO) will detect approximately 1,000 mergers of massive black holes annually once it achieves full sensitivity early next decade.
The prediction, published online June 22 in the journal Nature, is based on computer simulations of more than a billion evolving binary stars. The simulations are based on state-of-the-art modeling of the physics involved, informed by the most recent astronomical and astrophysical observations.
"The main thing we find is that what LIGO detected makes sense," said Daniel Holz, associate professor in physics and astronomy at the University of Chicago and a co-author of the Nature paper. The simulations predict the formation of black-hole binary stars in a range of masses that includes the two already observed. As more LIGO data become available, Holz and his colleagues will be able to test their results more rigorously.
The paper's lead author, Krzysztof Belczynski of Warsaw University in Poland, said he hopes the results will surprise him, that they will expose flaws in the work. Their calculations show, for example, that once LIGO reaches full sensitivity, it will detect only one pair of colliding neutron stars for every 1,000 detections of the far more massive black-hole collisions.
"Actually, I would love to be proven wrong on this issue. Then we will learn a lot," Belczynski said.
Forming big black holes
The new Nature paper, which includes co-authors Tomasz Bulik of Warsaw University and Richard O'Shaughnessy of the Rochester Institute of Technology, describes the most likely black-hole formation scenario that generated the first LIGO gravitational-wave detection in September 2015. That detection confirmed a major prediction of Albert Einstein's 1915 general theory of relativity.
The paper is the most recent in a series of publications, topping a decade of analyses where Holz, Belczynski and their associates theorize that the universe has produced many black-hole binaries in the mass range that are close enough to Earth for LIGO to detect.
"Here we simulate binary stars, how they evolve, turn into black holes and eventually get close enough to crash into each other and make gravitational waves that we would observe," Holz said.
The simulations show that the formation and evolution of a typical system of binary stars results in a merger of similar masses, and after similarly elapsed times, to the event that LIGO detected last September. These black hole mergers have masses ranging from 20 to 80 times more than the sun.
LIGO will begin recording more gravitational-wave-generating events as the system becomes more sensitive and operates for longer periods of time. LIGO will go through successive upgrades over the coming years, and is expected to reach its design sensitivity by 2020. By then, the Nature study predicts that LIGO might be detecting more than 100 black hole collisions annually.
LIGO has detected big black holes and big collisions, with a combined mass greater than 30 times that of the sun. These can only be formed out of big stars.
"To make those you need to have low metallicity stars, which just means that these stars have to be relatively pristine," Holz said. The Big Bang produced mainly hydrogen and helium, which eventually collapsed into stars.
As these stars burned they forged heavier elements, which astronomers call "metals." Those stars with fewer metals lose less mass as they burn, resulting in the formation of more massive black holes when they die. That most likely happened approximately two billion years after the Big Bang, before the young universe had time to form significant quantities of heavy metals. Most of those black holes would have merged relatively quickly after their formation.
LIGO would be unable to detect the ones that merged early and quickly. But if the binaries were formed in large enough numbers, a small fraction would survive for longer periods and would end up merging 11 billion years after the Big Bang (2.8 billion years ago), recently enough for LIGO to detect.
"That's in fact what we think happened," Holz said. Statistically speaking, "it's the most likely scenario." He added, however, that the universe continues to produce binary stars in local, still pristine pockets of low metallicity that resemble conditions of the early universe.
"In those pockets you can make these big stars, make the binaries, and then they'll merge right away and we would detect those as well."
Belczynski, Holz and collaborators have based their simulations on what they regard as the best models available. They assume "isolated formation," which involves two stars forming in a binary, evolving in tandem into black holes, and eventually merging with a burst of gravitational wave emission. A competing model is "dynamical formation," which focuses on regions of the galaxy that contain a high density of independently evolving stars. Eventually, many of them will find each other and form binaries.
"There are dynamical processes by which those black holes get closer and closer and eventually merge," Holz said. Identifying which black holes merged under which scenario is difficult. One potential method would entail examining the black holes' relative spins. Binary stars that evolved dynamically are expected to have randomly aligned spins; detecting a preference for aligned spins would be clear evidence in favor of the isolated evolutionary model.
LIGO is not yet able to precisely measure black hole spin alignment, "but we're starting to get there," Holz said. "This study represents the first steps in the birth of the entirely new field of gravitational wave astronomy. We have been waiting for a century, and the future has finally arrived."
Citation: "The first gravitational-wave source from the isolated evolution of two stars in the 40-100 solar mass range," by Krzysztof Belczynski, Daniel E. Holz, Tomasz Bulik, and Richard Oâ€™Shaughnessy," Nature, Vol. 534, pp. 512-515, June 23, 2016, doi:10.1038/nature18322.
Department members: Daniel E. Holz
Gravitational waves detected from second pair of colliding black holes
June 16, 2016
At 9:38:53 CST on Dec. 25, 2015, scientists observed gravitational waves - ripples in the fabric of spacetime - for the second time.
The gravitational waves were detected by both of the twin Laser Interferometer Gravitational-Wave Observatory detectors, located in Livingston, La., and Hanford, Wash. University of Chicago scientists led by Daniel Holz, assistant professor in physics and astronomy, are members of the LIGO collaboration.
The LIGO observatories are funded by the National Science Foundation, and were conceived, built and are operated by the California Institute of Technology and the Massachusetts Institute of Technology. The discovery, accepted for publication in the journal Physical Review Letters, was made by the LIGO Scientific Collaboration and the Virgo Collaboration using data from the two LIGO detectors.
The LIGO detectors operated for approximately four months late last year, yielding about 50 days of data. An analysis of the first 16 days of data yielded the event that the LIGO Collaboration announced in February 2016.
Black holes events
"Now weâ€™ve analyzed the rest of the data, and we have another event thatâ€™s particularly interesting," Holz said. "It's not quite as loud as the first one, but it's quite beautiful in its own way. The event is composed of smaller black holes, and at least one is spinning. This marks the official turning point from 'detector' to 'observatory.'"
Gravitational waves carry information about their origins and about the nature of gravity that cannot otherwise be obtained, and physicists have concluded that these gravitational waves were produced during the final moments of the merger of two black holes - 14 and 8 times the mass of the sun - to produce a single, more massive spinning black hole that is 21 times the mass of the sun.
"It is very significant that these black holes were much less massive than those observed in the first detection," said Gabriela Gonzalez, LIGO Scientific Collaboration spokesperson and professor of physics and astronomy at Louisiana State University. "Because of their lighter masses compared to the first detection, they spent more time - about one second - in the sensitive band of the detectors. It is a promising start to mapping the populations of black holes in our universe."
During the merger, which occurred approximately 1.4 billion years ago, a quantity of energy roughly equivalent to the mass of the sun was converted into gravitational waves. The detected signal comes from the last 27 orbits of the black holes before their merger. Based on the arrival time of the signals - with the Livingston detector measuring the waves 1.1 milliseconds before the Hanford detector - the position of the source in the sky can be roughly determined.
The first detection of gravitational waves, announced on Feb. 11, 2016, was a milestone in physics and astronomy: It confirmed a major prediction of Albert Einstein's 1915 general theory of relativity, and marked the beginning of the new field of gravitational wave astronomy.
Both discoveries were made possible by the enhanced capabilities of Advanced LIGO, a major upgrade that increases the sensitivity of the instruments compared to the first-generation LIGO detectors, enabling a large increase in the volume of the universe probed.
'With the advent of Advanced LIGO, we anticipated researchers would eventually succeed at detecting unexpected phenomena, but these two detections thus far have surpassed our expectations,' said NSF Director France A. Cordova. "NSF's 40-year investment in this foundational research is already yielding new information about the nature of the dark universe."
Advanced LIGO's next data-taking run will begin this fall. By then, further improvements in detector sensitivity are expected to allow LIGO to reach as much as 1.5 to 2 times more of the volume of the universe. The Virgo detector is expected to join in the latter half of the coming observing run.
LIGO research is carried out by the LIGO Scientific Collaboration, a group of more than 1,000 scientists from universities around the United States and in 14 other countries. More than 90 universities and research institutes in the LSC develop detector technology and analyze data; approximately 250 students are strong contributing members of the collaboration. Virgo research is carried out by the Virgo Collaboration, consisting of more than 250 physicists and engineers belonging to 19 different European research groups.
Department members: Daniel E. Holz
Wendy Freedman Named 2016 Woman in Space Science
May 23, 2016
On Thursday, May 12, Chicago's Adler Planetarium presented the 2016 Women in Space Science Award to Wendy L. Freedman, the John & Marion Sullivan Professor of Astronomy & Astrophysics.
The annual Women in Space Science Award recognizes women who have made significant contributions to the fields of science, technology, engineering, and math (STEM) with the goal of inspiring young women to pursue careers in these disciplines. Following a luncheon and her keynote address, Professor Freedman joined approximately 250 young women from Chicago-area public schools for a series of engaging STEM workshops.
One of Professor Freedmanâ€™s many achievements was initiating the Giant Magellan Telescope (GMT) Project and serving as chair of the board of directors from its inception in 2003 until 2015. The Division of the Physical Sciences joins the Adler in celebrating Wendyâ€™s accomplishments and looking forward to the amazing discoveries that await her and the GMT.
Department members: Wendy L. Freedman
Department students: Megan Bedell, Maya Fishbach, Laura Kreidberg, Nora Shipp
Scientific projects: Giant Magellan Telescope
Quartet of exoplanets locked in complex dance
May 11, 2016
UChicago News, by Steve Koppes
The four planets of the Kepler-223 star system seem to have little in common with the planets of Earths own solar system. And yet a new study shows that the Kepler-223 system is trapped in an orbital configuration that Jupiter, Saturn, Uranus and Neptune may have broken out of in the early history of the solar system.
All four of the puffy, gaseous planets are far more massive than Earth and orbit extremely close to their nearest star-closer than Mercury is to our sun. Their orbits also are locked together in a precise pattern, raising the question of whether the gas giants in our solar system somehow escaped a similar configuration in the distant past.
"Exactly how and where planets form is an outstanding question in planetary science," said the study's lead author, Sean Mills, a graduate student in astronomy & astrophysics at the University of Chicago. "Our work essentially tests a model for planet formation for a type of planet we don't have in our solar system."
Because the orbital configuration is so different than the one in our system, Mills said, there's a big debate about how such planets form, how they got there and why Earth's system turned out as it did.
Department members: Daniel Fabrycky
Department students: Sean Mills
Astronomers find a system of planets that keep each other in the tightest formation seen
May 11, 2016
Astronomy Magazine, by John Wenz
With each planet in resonance, there's little room to move for the four planets around Kepler-223.
There's something strange going on in the Kepler-223 system. Four sub-Neptune-size worlds migrated close into their star at some point, and they never migrated back out. They hold such a tight resonance that theyâ€™ve since been unable to move out of that configuration.
A paper today in Nature details the weird workings of the system. For every three orbits that Kepler-223b makes, Kepler-223c makes four. For every two orbits that Kepler-223c makes, Kepler-223d makes three. And for every one of those three, Kepler-223e makes four. It's so tightly packed that it precludes any large moons, or even nearby planets that might tug any of these planets out of the tight resonance.
Add in that this system is far older than the Sun and you have a weird, weird system.
"This is a unique case in the Kepler data and all of nature, really, that four planets are in resonance with one another," said Dan Fabrycky, an assistant professor at the University of Chicago and a co-author on the paper.
Sean Mills, a graduate student at the University of Chicago and lead author of the paper, ran the numbers on these swiftly moving worlds. Kepler-223b orbits in 7 days and Kepler-223e orbits in 20 days.
Department members: Daniel Fabrycky
Department students: Sean Mills
Prof. Michael Turner's May 5 lecture at Adler Planetarium to be simulcast nationally
May 5, 2016
UChicago News, by Steve Koppes
Prof. Michael Turner will explore some of the biggest mysteries of modern cosmology in a 7:30 p.m. May 5 lecture at the Adler Planetarium. The cosmologistâ€™s Kavli Fulldome Lecture, titled "From the Big Bang to the Multiverse and Beyond," will be streamed live at 15 other institutions across North America.
Kavli Fulldome Lecture
Is the universe part of a larger multiverse? What is speeding up the expansion of the universe? Turner will address these and other mysteries that inspire modern cosmologists. His talk will stream live simultaneously at 15 other institutions across North America. This dome-cast will allow audiences across North America to immerse themselves in the live presentation and ask questions, and will include institutions like the American Museum of Natural History in New York City, the Pacific Science Center in Seattle and the H.R. MacMillan Space Centre in Vancouver, British Columbia.
A theoretical astrophysicist, Turner is the Bruce V. and Diana M. Rauner Distinguished Service Professor and director of its Kavli Institute for Cosmological Physics. Turner helped to pioneer the interdisciplinary field of particle astrophysics and cosmology. He has made seminal contributions to the current cosmological paradigm known as LambdaCDM, including the prediction of cosmic acceleration. Turner has received numerous prizes and is a member of the National Academy of Sciences.
Current list of institutions participating in the dome-cast:
Department members: Michael S. Turner
Joshua Frieman elected to American Academy of Arts and Sciences
April 26, 2016
UChicago News, by Mary Abowd and Steve Koppes
Joshua Frieman is a professor of astronomy & astrophysics and the College. He is also a member of the Kavli Institute for Cosmological Physics at UChicago and a member of the theoretical astrophysics group at Fermi National Accelerator Laboratory. He focuses his research on theoretical and observational cosmology, including studies of the nature of dark energy, the early universe, gravitational lensing, the large-scale structure of the universe and supernovae as cosmological distance indicators.
Frieman is a co-founder and director of the Dark Energy Survey, an international collaboration of more than 300 scientists from 25 institutions on three continents that investigates why the expansion of the universe is accelerating. The collaboration built a 570-megapixel camera for the four-meter Blanco Telescope at the Cerro Tololo Inter-American Observatory in Chile to conduct its observations. Previously Frieman led the Sloan Digital Sky Survey Supernova Survey, which discovered more than 500 type Ia supernovae for cosmological studies.
Frieman is an honorary fellow of the Royal Astronomical Society, and a fellow of the American Physical Society and of the American Association for the Advancement of Science.
Department members: Joshua A. Frieman
Scientific projects: Dark Energy Survey