Research, teaching and outreach in Physics at UW–Madison
Earth-sized planet discovered in ‘our solar backyard’
A team of astronomers have discovered a planet closer and younger than any other Earth-sized world yet identified. It’s a remarkably hot world whose proximity to our own planet and to a star like our sun mark it as a unique opportunity to study how planets evolve.
In the culmination of a decade’s worth of effort, the Dark Energy Survey collaboration of scientists analyzed an unprecedented sample of nearly 1,500 supernovae classified using machine learning. They placed the strongest constraints on the expansion of the universe ever obtained with the DES supernova survey. While consistent with the current standard cosmological model, the results do not rule out a more complex theory that the density of dark energy in the universe could have varied over time.
DES scientists presented the results January 8 at the 243rd meeting of the American Astronomical Society and have submitted them for publication to the Astrophysical Journal.
The work is the output of over 400 DES scientists, including UW–Madison physics professor Keith Bechtol and former graduate student Robert Morgan, PhD ’22.
In 1998, astrophysicists discovered that the universe is expanding at an accelerating rate, attributed to a mysterious entity called dark energy that makes up about 70% of our universe. While foreshadowed by earlier measurements, the discovery was somewhat of a surprise; at the time, astrophysicists agreed that the universe’s expansion should be slowing down because of gravity.
This revolutionary discovery, which astrophysicists achieved with observations of specific kinds of exploding stars, called type Ia (read “type one-A”) supernovae, was recognized with the Nobel Prize in Physics in 2011.
In this new study, DES scientists performed analyses with four different techniques, including the supernova technique used in 1998, to understand the nature of dark energy and to measure the expansion rate of the universe.
As a graduate student in Bechtol’s group, Morgan was part of the DES supernova working group that worked to identify type Ia supernova. This group had to address two main concerns with the data to enhance detection fidelity.
“One is that there is some leakage of other types of supernovae into the sample, so you have to calibrate the rate of misclassification,” Bechtol explains. “Also, the brightness of the supernova gives us a way of estimating its distance, but there is a distribution of how bright the Ia supernovae are. Because we are slightly less likely to detect the intrinsically fainter supernovae, there is a small bias that needs to be accounted for.”
Bechtol has been part of the DES collaboration since its formation in 2012, serving as a co-convener of the DES’s Science Release Working Group for four years and a co-convener of the Milky Way Working Group for two years. His role in this new study was in data processing and presentation.
“We collect all of the data, process it, and then release it as a coherent set of data products, both for use by the DES collaboration and as part of public releases to the community,” Bechtol says. “One of the aspects I worked on is the photometric calibration — our ability to measure the fluxes of objects accurately and precisely. It’s an important part of the supernova analysis and something that I’ve been working on continuously over the past ten years.”
Physics PhD student Stephen McKay named ALMA ambassador
Congrats to physics graduate student Stephen McKay on being named an ALMA ambassador!
ALMA, or the Atacama Large Millimeter/submillimeter Array, is the largest radio telescope in the world. It can detect light radiated by clouds of dust grains in some of the earliest and most distant galaxies in the Universe. Researchers can submit proposals to ALMA that direct data collection to observe astronomical targets at a wide range of wavelengths, in order to accomplish many cutting-edge science goals. However, ALMA receives many more proposals than there is time to operate the telescope.
That’s where McKay’s ambassadorship comes in.
“Lots of groups at UW–Madison and other places will propose to get data from these telescope arrays,” McKay says. “In February, I’ll attend a training (through the ambassador program) where they will teach me tips and tricks for writing proposals. Then in early spring, I’ll run a proposal workshop here for anyone who wants to learn how to strengthen a proposal.”
McKay is no stranger to proposing and using ALMA data. A third-year graduate student in astronomy professor Amy Barger’s research group, he expects nearly all his publications will be based on ALMA data. His research focuses on old, distant galaxies and measuring and inferring physical properties about them: How massive are they? What is their rate of star formation? What processes trigger the rapid star-formation in these systems?
“The galaxies that I mainly study are faint or hard to detect in optical wavelengths or even near-infrared wavelengths. Until about maybe 25 years ago, we didn’t know a lot of these galaxies existed because they just weren’t visible in the typical telescope images we had,” McKay says. “The portion of the observed electromagnetic spectrum where these galaxies are brightest ranges from 500 microns to nearly one millimeter, which overlaps heavily with ALMA’s spectral coverage.”
Two years ago, McKay attended an ALMA workshop to learn more about how ALMA and similar radio arrays operate. With this ALMA ambassadorship, he will now help run the workshops and offer advice on crafting stronger proposals. The ALMA Ambassador Program is run through the National Radio Astronomy Observatory’s North American ALMA Science Center (NAASC). It provides training and an up to $10,000 research grant to early-career researchers interested in expanding their ALMA/interferometry expertise and sharing that knowledge with their home institutions.
“This program is helpful for me because I will learn more in terms of how to actually do my own research, but then I can also pass along what I learn with the rest of the astronomical community,” McKay says.
Jimena González joins Bouchet Graduate Honor Society
Five outstanding scholars, including Physics PhD student Jimena González, are joining the UW–Madison chapter of the national Edward Alexander Bouchet Graduate Honor Society this academic year.
The Bouchet Society commemorates the first person of African heritage to earn a PhD in the United States. Edward A. Bouchet earned a PhD in Physics from Yale University in 1876. Since then, the Bouchet Society has continued to uphold Dr. Bouchet’s legacy.
“The 2024 Bouchet inductees are making key contributions in their disciplines, as well as to the research, education, and outreach missions of our campus. They truly embody the Wisconsin Idea and are exemplary in every way,” said Abbey Thompson, assistant dean for diversity, inclusion, and funding in the Graduate School.
The Bouchet Society serves as a network for scholars that uphold the same personal and academic excellence that Dr. Bouchet demonstrated. Inductees to the UW–Madison Chapter of the Bouchet Society also join a national network with 20 chapters across the U.S. and are invited to present their work at the Bouchet Annual Conference at Yale University, where the scholars further create connections and community within the national Bouchet Society.
The UW–Madison Division of Diversity, Equity, and Educational Achievement supports each inductee with a professional development grant.
González is a physics PhD candidate specializing in observational cosmology. Her research centers on searching and characterizing strong gravitational lenses in the Dark Energy Survey. These rare astronomical systems can appear as long curved arcs of light surrounding a galaxy. Strong gravitational lenses offer a unique probe for studying dark energy, the driving force behind the universe’s accelerating expansion and, consequently, a pivotal factor in determining its ultimate fate.
During her graduate program, Jimena has received the Albert R. Erwin, Jr. & Casey Durandet Award and the Firminhac Fellowship from the Department of Physics. Additionally, she was honored with the 2023 Open Science Grid David Swanson Award for her outstanding implementation of High-Throughput Computing to advance her research. Jimena has contributed as a co-author to multiple publications within the field of strong gravitational lensing and has presented her work at various conferences. In addition to her academic achievements, Jimena has actively engaged in outreach programs. Notably, she was selected as a finalist at the 2021 UW–Madison Three Minute Thesis Competition and secured a winning entry in the 2023 Cool Science Image Contest. Her commitment to science communication extends to a contribution in a Cosmology chapter in the book AI for Physics. Jimena has also led a citizen science project that invites individuals from all around the world to inspect astronomical images to identify strong gravitational lenses. Jimena obtained her bachelor’s degree in physics at the Universidad de los Andes, where she was awarded the “Quiero Estudiar” scholarship.
Federal physics advisory panel — including Profs. Bose and Cranmer — announces particle physics recommendations
Earlier this year, physics professors Tulika Bose and Kyle Cranmer were selected to serve on the Particle Physics Project Prioritization Panel, or P5, a group of High Energy Physics experts that advises the Department of Energy Office of Science and the National Science Foundation’s Division of Physics on high energy and particle physics matters.
One recommendation is to move forward with a planned expansion of the IceCube Neutrino Observatory, an international scientific collaboration operated by the UW–Madison at the South Pole. Other recommendations include support for a separate neutrino experiment based in Illinois (the Deep Underground Neutrino Experiment, or DUNE); continuing investment in the Large Hadron Collider in Switzerland and the Rubin Observatory in Chile; and expanding involvement in the Cherenkov Telescope Array (CTA), a ground-based very-high-energy gamma ray observatory. UW–Madison physicists have leading roles in all of these research efforts.
Additional recommendations include the development of a next generation of ground-based telescopes to observe the cosmic microwave background and a direct dark matter detector experiment, among others.
To better understand the nature of dark energy, she uses machine learning to search Dark Energy Survey cosmology data for evidence of strong gravitational lensing — where a heavy foreground galaxy bends the light of another galaxy, producing multiple images of it that can get so distorted that they appear as long arcs of light around the large galaxy in telescope images. She also focuses on finding very rare cases of strong gravitational lensing in which two galaxies are lensed by the same foreground galaxy, systems known as double-source-plane lenses.
First, she had to create simulations of the galaxy systems. Next, she used those simulations to train the machine learning model to identify the systems in the heaps and heaps of DES data. Lastly, she would apply the trained model to the real DES data. All told, she expected to find hundreds of “simple” strong gravitational lenses and only a few double-source-plane lenses out of 230 million images.
“But, for example, when I did the search the first time, I mostly only got spiral galaxies, so then I had to include spiral galaxies in my training,” says González, a physics graduate student in Keith Bechtol’s group.
The initial steps took around two weeks (hence the waiting) before she could even know what needed to be changed to better train the model. Once she had the model trained and would be ready to apply it to the entire dataset, she estimated it would take five to six years just to find the images of interest — and then she would finally be able to study the systems found.
Then, the email from the Open Science Grid (OSG) Consortium came. The OSG Consortium operates a fabric of distributed High Throughput Computing (dHTC) services, allowing users to take advantage of massive amounts of computing power. Researchers can apply to the OSG User School, an annual workshop for scientists who want to learn and use dHTC methods.
“[dHTC] is parallelizing things. It’s like if you had 500 exams to grade, you can distribute them among different people and it would take less time,” González says. “It sounded perfect for me.”
González applied and was accepted into the 2021 program, which was run virtually that year. At the OSG User School, she learned methods that would allow her to take advantage of dHTC and apply them to her work. Her multi-year processing time was cut down to mere days.
“Because it was so fast, there were many new things that I could implement in my research,” González says. “A lot of the methodology I implemented would not have been possible without OSG.”
David Swanson was a longtime champion of and contributor to OSG, who passed away in 2016. In his memory, the award is bestowed annually upon one or more former students of the OSG User School who have subsequently achieved significant dHTC-enabled research outcomes.
She accepted the award at the Throughput Computing 2023 conference, where she presented her research and discussed how she used her training from the OSG User School to successfully comb through the DES data and find the systems of interest.
“When I got the award, I didn’t know anything about [Swanson],” González says. “But once I attended this event, I heard so many people talking about him, and I understood why it was created. It is such an honor to receive this award in his name.”
Through machine learning maps, cosmic history comes into focus
By Jason Daley, UW–Madison College of Engineering
For millennia, humans have used optical telescopes, radio telescopes and space telescopes to get a better view of the heavens.
Today, however, one of the most powerful tools for understanding the cosmos is the computer chip: Cosmologists rely on processing power to analyze astronomical data and create detailed simulations of cosmic evolution, galaxy formation and other far-out phenomena. These powerful simulations are starting to answer fundamental questions of how the universe began, what it is made of and where it’s likely headed.
“It is extremely expensive to run these simulations and basically takes forever,” says Kangwook Lee, an assistant professor of electrical and computer engineering at the University of Wisconsin-Madison. “So they cannot run them for large-scale simulations or for high-resolution at that same time. There are a lot of issues coming from that.”
Instead, machine learning expert Lee and physics colleagues Moritz Münchmeyer and Gary Shiu are using emerging artificial intelligence techniques to speed up the process and get a clearer view of the cosmos.
Keith Bechtol, Victor Brar promoted to Associate Professors
Congratulations to Keith Bechtol and Victor Brar, who were both promoted to associate professors of physics with tenure!
Bechtol is an observational cosmologist with research interests in dark matter and dark energy, using the whole Universe as a lab to understand the fundamental physics of nature. He is part of the Dark Energy Survey (DES) that has cataloged more 500 million galaxies and thousands of supernovae to understand the nature of dark energy. He and his group are also working on the construction and commissioning of the Vera C. Rubin Observatory in preparation for the Legacy Survey of Space and Time (LSST). LSST is expected to catalog more stars, more galaxies and more solar system objects during its first year of operations than all previous telescopes combined.
“Professor Bechtol plays a leading role in the Vera C. Rubin Observatory, which is now poised to enable a major leap in the data available for understanding the development of our universe,” says Mark Eriksson, Chair and John Bardeen Professor of Physics.
Bechtol was a co-convener of the DES’s Science Release Working Group for four years and a co-convener of the Milky Way Working Group for two years. He is now serving as Technical Coordinator for the LSST Dark Energy Science Collaboration. In 2022, he was selected to the Department of Energy’s Early Career Research Program. He also proposed and is the faculty lead for the physics department’s Thaxton Fellowship, whose goal is to provide more equitable access to physics research experiences for undergraduates.
Brar, the Van Vleck professor of physics and a member of the Wisconsin Quantum Institute, is an experimental condensed matter physicist with a research focus on quantum materials and novel imaging techniques. His group works on developing metamaterials such as 2D materials for use in laser sailing or fabricating graphene structures for use in telecommunications. They also use scanning tunneling microscopy and scanning tunneling potentiometry to understand the physical and electrical properties of materials.
“The experiments performed by Professor Brar and his research team have enabled measurements of completely new regimes for electron transport in 2D materials,” Eriksson says.
Brar was awarded a Moore Inventor Fellowship in 2018, a Sloan Fellowship in 2021, and a National Science Foundation CAREER award in 2023. He has additionally received two UW–Madison Research Forward awards.
Sau Lan Wu honored with named planet
The International Astronomical Union (IAU) has named a minor planet ‘Saulanwu’ after UW–Madison physics professor Sau Lan Wu.
The planet (177770) ‘Saulanwu’ (=2005 JE163) was discovered on May 8, 2005 at Mt Lemmon observatory in southern Arizona by a NASA funded project, the Catalina Sky Survey. More details about the planet can be found from NASA’s JPL website, including a sketch of the planet’s orbit, which is in the asteroid belt between Mars and Jupiter. Minor planet ‘Saulanwu’ is about two kilometers in diameter, and it takes four years to orbit the sun once. This planet is relatively stable, dynamically, and is expected to remain in our cosmos for millions of years to come.
Wu was nominated for this honor by astronomer Gregory J. Leonard from the University of Arizona’s Department of Planetary Sciences.
Keith Bechtol selected to Department of Energy Early Career Research Program
The funding will allow Bechtol and his group to first work on commissioning the Vera C. Rubin Observatory in preparation for the Legacy Survey of Space and Time (LSST), then they will transition to data collection and analysis for their cosmology research.
“We are anticipating that LSST will catalog more stars, more galaxies and more solar system objects during its first year of operations than all previous telescopes combined,” Bechtol says.
Rubin Observatory’s telescope will have an eight-meter diameter mirror and a ten square degree field of view. The 3.2-billion-pixel camera will collect an image every 30 seconds. All told, LSST will amass around 10 terabytes of data every night.
Bechtol has leadership roles for building and commissioning the observatory as well as with the Dark Energy Science Collaboration (DESC), the international science collaboration that will make high accuracy measurements of fundamental cosmological parameters using LSST data. At least seven other collaborations have formed around different science areas to analyze the data. Rubin Observatory is preparing to serve the LSST data to many thousands of scientists in the US, Chile, and at international partner institutions around the world.
“DESC will use LSST data to address several outstanding physics questions, such as: Why are the distances between galaxies growing at an accelerating rate? What is the fundamental nature of dark matter? What is the absolute mass scale of neutrinos? How did the universe begin and what were the initial conditions?” Bechtol says.
Bechtol will receive around $150,000 per year for five years to cover summer salary and research expenses. The research expenses will be used mostly to cover the analyses after the data collection starts. However, because there cannot be useful data without the initial commissioning and science validation steps — and because the Observatory is still a couple of years away from first light — the DOE award is also supporting Bechtol’s efforts during the commissioning phase to accelerate the realization of DESC science goals.
“For me, the most important thing about this award is that it will provide more opportunity for students and postdocs to directly contribute to this ambitious experiment. Turning on a new experiment of this scale and complexity doesn’t happen every day,” Bechtol says. “For my research group to be able to participate firsthand in the commissioning, seeing first light, and contributing to the first cosmology results is so valuable from a career development perspective. We are training the next generation of experiment builders.”
The DOE early career program is open to untenured, tenure-track professors at a U.S. academic institution (or a full-time employee at a DOE national laboratory) who received a PhD within the past 10 years. Research topics are required to fall within one of the DOE Office of Science’s eight major program offices, including high energy physics, the program through which Bechtol’s award was made.