Research, teaching and outreach in Physics at UW–Madison
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Ke Fang named Sloan Fellow
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This story is adapted from one published by University Communications
Ke Fang
Ke Fang, assistant professor of Physics and WIPAC investigator, is among 126 scientists across the United States and Canada selected as Sloan Research Fellows.
The fellowships, awarded annually since 1955, honor exceptional scientists whose creativity, innovation and research accomplishments make them stand out as future leaders in their fields.
Using data from the Ice Cube Observatory and Fermi Large Area Telescope along with numerical simulations, Fang studies the origin of subatomic particles — like neutrinos — that reach Earth from across the universe.
“Sloan Research Fellowships are extraordinarily competitive awards involving the nominations of the most inventive and impactful early-career scientists across the U.S. and Canada,” says Adam F. Falk, president of the Alfred P. Sloan Foundation. “We look forward to seeing how fellows take leading roles shaping the research agenda within their respective fields.”
Founded in 1934, the Sloan Foundation is a not-for-profit institution dedicated to improving the welfare of all through the advancement of scientific knowledge.
Sloan Fellows are chosen in seven fields — chemistry, computer science, Earth system science, economics, mathematics, neuroscience and physics — based on nomination and consideration by fellow scientists. The 2024 cohort comes from 53 institutions and a field that included more than 1,000 nominees. Winners receive a two-year, $75,000 fellowship that can be used flexibly to advance their research.
Among current and former Sloan Fellows, 57 have won a Nobel Prize, 71 have been awarded the National Medal of Science, 17 have won the Fields Medal in mathematics and 23 have won the John Bates Clark Medal in economics.
Xiangyao Yu, assistant professor of computer sciences at UW–Madison, was also named a Sloan Fellow.
Tulika Bose, co-organizer of PURSUE, featured in Symmetry article
The largest magnetic fields in galaxy clusters have been revealed for the first time
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By Alex Lazarian, Yue Hu, and Ka Wai Ho
Galaxy clusters, immense assemblies of galaxies, gas, and elusive dark matter, form the cornerstone of our Universe’s grandest structure — the cosmic web. These clusters are not just gravitational anchors, but dynamic realms profoundly influenced by magnetism. The magnetic fields within these clusters are pivotal, shaping the evolution of these cosmic giants. They orchestrate the flow of matter and energy, directing accretion and thermal flows, and are vital in accelerating and confining high-energy charged particles/cosmic rays.
However, mapping the magnetic fields on the scale of galaxy clusters posed a formidable challenge. The vast distances and complex interactions with magnetized and turbulent plasmas diminish the polarization signal, a traditionally used informant of magnetic fields. Here, the groundbreaking technique — synchrotron intensity gradients (SIG) — developed by a team of UW–Madison astronomers and physicists led by astronomy professor Alexandre Lazarian, marks a turning point. They shifted the focus from polarization to the spatial variations in synchrotron intensity. This innovative approach peels back layers of cosmic mystery, offering a new way to observe and comprehend the all-important magnetic tapestry on scale of millions of light years.
A landmark study published in Nature Communications has employed the SIG technique to unveil the enigmatic magnetic fields within five colossal galaxy clusters, including the monumental El Gordo cluster, observed with the Very Large Array (VLA) and MeerKAT telescope. This colossal cluster, formed 6.5 billion years ago, represents a significant portion of cosmic history, dating back to nearly half the current age of the universe. The findings in El Gordo, characterized by the largest magnetic fields observed, provide crucial insights into the structure and evolution of galaxy clusters.
Left: Image of the El Gordo cluster observed Chandra X-ray Observatory and ground-based optical telescopes (credits: NASA/ESA/CSA). Magnetic field visualized by streamlines are superimposed on the image. Right: images of the Fishhook galaxy (top) and Milky Way (bottom).
The research is a fruitful collaboration between the UW–Madison team and their Italian colleagues, including Gianfranco Brunetti, Annalisa Bonafede, and Chiara Stuardi from the Instituto do Radioastronomia (Bologna, Italy) and the University of Bologna. Brunetti, a renowned expert in the high-energy physics of galaxy clusters, is enthusiastic about the potential that the SIG technique holds for exploring magnetic field structures on even larger scales, such as the Megahalos recently discovered by him and his colleagues.
Echoing this excitement is the study’s lead researcher, physics graduate student Yue Hu.
“This research marks a significant milestone in astrophysics,” Hu says. “Utilizing the SIG method, we’ve observed and begun to comprehend the nature of magnetic fields in galaxy clusters for the first time. This breakthrough heralds new possibilities in our quest to unravel the mysteries of the universe.”
This study lays the groundwork for future explorations. With the SIG method’s proven effectiveness, scientists are optimistic about its application to even larger cosmic structures that have been detected recently with the Square Kilometre Array (SKA), promising deeper insights into the mysteries of the Universe magnetism and its effects on the evolution of the Universe Large Scale Structure.
First field season for IceCube Upgrade ongoing at the South Pole
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Over the past two months, a team of IceCube drill engineers have completed an impressive amount of work during the first of three consecutive field seasons for the IceCube Upgrade. The project is funded by the National Science Foundation and international collaborators.
The goal of the project is to drill seven holes in 2025/2026 and deploy seven more closely spaced and more densely instrumented strings of sensors in the central part of the array, which will improve IceCube’s sensitivity to low energies. Having a productive first field season both sets the Upgrade project up for success and trains the new generation of drillers at the South Pole.
The majority of the team’s engineers come from the University of Wisconsin–Madison’s Physical Sciences Laboratory (PSL), where equipment is fabricated and shipped to the South Pole. Additional drill engineers hail from Sweden, New Zealand, and for the first time, Thailand.
“This year’s drill team is a group of 17 talented professionals who have completed an enormous amount of work,” says Kurt Studt, drill engineer at PSL and the on-ice drill manager for the Upgrade. “We’ve overcome many difficult challenges while dealing with the extreme environment at the South Pole, including temperatures as low as -35 ⁰F and windchills below -60 ⁰F.”
The IFD “carrot” drill head (left) drills a 40-meter hole in the firn (right). Credit: Kurt Studt, IceCube/NSF
Earth-sized planet discovered in ‘our solar backyard’
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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.
The new planet was described in a new study published this week by The Astronomical Journal. Melinda Soares-Furtado, a NASA Hubble Fellow at the University of Wisconsin–Madison who will begin work as an astronomy and physics professor at the university in the fall, and recent UW–Madison graduate Benjamin Capistrant, now a graduate student at the University of Florida, co-led the study with co-authors from around the world.
“It’s a useful planet because it may be like an early Earth,” says Soares-Furtado.
Young, hot, Earth-sized planet HD 63433d sits close to its star in the constellation Ursa Major, while two neighboring, mini-Neptune-sized planets — identified in 2020 — orbit farther out. Illustration: Alyssa Jankowski
UW physicists part of study offering unique insights into the expansion of the universe
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.
An example of a supernova discovered by the Dark Energy Survey within the field covered by one of the individual detectors in the Dark Energy Camera. The supernova exploded in a spiral galaxy with redshift = 0.04528, which corresponds to a light-travel time of about 0.6 billion years. This is one of the nearest supernovae in the sample. In the inset, the supernova is a small dot at the upper-right of the bright galaxy center. Image: DES collaboration
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.
Keith Bechtol
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.”
Navigating new tech: Kael Hanson earns Draper Technology Innovation Fund award
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Kael Hanson
Celestial navigation — charting a course through a combination of identifying star positions in the sky and knowing the time — has existed for centuries and is considerably low-res compared to modern GPS systems. So why did physics professor Kael Hanson recently receive a Draper Technology Innovation Fund (TIF) award for an invention that is based off of it?
“The pain that we’re trying to address with this technology is vulnerabilities in GPS,” Hanson says. “Everyone uses GPS, but if it drops out or gets jammed, that could be a problem, especially for the military or commercial industries like aviation or shipping that rely on it to be working and accurate 100% of the time.”
GPS is vulnerable because the satellites’ weak signals can be easily drowned out by stronger signals. Its function is susceptible to both natural (e.g. strong solar flares) and man-made (e.g. jamming or intentional signal spoofing) incidents.
Distant stars and galaxies, however, remain unaffected by whatever is happening on or near earth, so they are useful visual points of reference — unless the current conditions include daylight, clouds, or fog. Hanson’s invention, known as GRADIANT, reverts to the same concept as celestial navigation, but with a modern twist to avoid any visibility issues.
“Charged particles spinning around in the magnetic fields of our galaxy give off synchrotron radiation at radio frequencies. This technology images the sky in radio frequencies,” Hanson says. “And by doing that, basically you can see through clouds. Our technology is reliably good in all scenarios.”
Radio astronomers have been cataloging radio data for decades, and the signals remain mostly static throughout time. The invention would detect radio frequencies at the user’s location, be computationally compared to the wealth of catalogued data, and then tell the user where they are.
Hanson is not exactly sure where he came up with this idea, but he thinks it came to him when he was at the South Pole 10-15 years ago working on the Askaryan Radio Array (ARA), a radio detector installed below the ice (it is co-deployed with IceCube, which is operated by WIPAC, of which Hanson was director from 2014-2022).
These two images of the sky are looking at the same sky but at different wavelengths. The left is optical, what you would see if you looked up on a clear night. The right is at radio frequencies. There are still plenty of objects that can be used to determine position, but the right image would be seen under a thick, overcast sky. Credit: Navigationis
“One of the background signals was the sun, and I thought ‘Oh, we can actually image the sun a couple hundred meters under the ice. Boy, wouldn’t that be interesting if you could somehow use this technology to try to figure out where you are based on where the sun is?’” Hanson says. “But then I just stuffed it away in my brain and didn’t really think about it (until recently).”
In 2021, Hanson started a company, Navigationis, to pursue his modern celestial navigation idea. This past summer, he submitted a disclosure for GRADIANT to WARF, for which a patent has now been filed. Then, he applied for and was awarded the Draper TIF funding.
Draper TIF provides a mechanism to support additional research necessary to bring new concepts and inventions to the patent and licensing stage. A main goal of the program is the eventual introduction of new products and processes into the marketplace for the public good. It is open to UW–Madison faculty and academic staff. The program is administered in partnership between Discovery to Product and the Wisconsin Alumni Research Foundation.
Hanson’s award provides $50,000, which he will use to try to make the technology more licensable.
“In order to really get this thing to the commercial state, it will take millions of dollars, it will take some additional investment,” Hanson says. “With this Draper TIF, we’re going to put together a prototype that actually proves in real hardware the working concept that’s in the patent. My hope is that I’ll have something I can point to, and venture capitalists will be that much more interested in making an investment, or the Department of Defense would be interested in supporting this work.”
Physics PhD student Stephen McKay named ALMA ambassador
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Stephen McKay
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.”
In the Chajnantor Plateau, amazing picture of the antennas under the Milkyway. Credit: Sergio Otarola- ALMA (ESO/NAOJ/NRAO)
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.
Jimena González
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.
Welcome, Professor Vladimir Zhdankin!
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Vladimir Zhdankin (credit: Flatiron Institute)
Theoretical plasma astrophysicist Vladimir Zhdankin ‘11, PhD ’15, returns to UW–Madison as an assistant professor of physics on January 1, 2024. As a student, Zhdankin worked with Prof. Stas Boldyrev on solar wind turbulence and basic magnetohydrodynamic turbulence, which are relevant for near-Earth types of space plasmas. After graduating, Zhdankin began studying plasma astrophysics of more extreme environments. He first completed a postdoc at CU-Boulder, then a NASA Einstein Fellowship at Princeton University. He joins the department from the Flatiron Institute in New York, where he is currently a Flatiron Research Fellow.
Please give an overview of your research.
These days, most of my interest is in the field of plasma astrophysics — the application of plasma physics to astrophysical problems. Much of the matter in the universe is in a plasma state, such as stars, the matter around black holes, and the interstellar medium in the galaxy. I’m interested in understanding the plasma processes in those types of systems. My focus is particularly on really high energy systems, like plasmas around black holes or neutron stars, which are dense objects where you could get extreme plasmas where relativistic effects are important. The particles are traveling at very close to the speed of light, and there’s natural particle acceleration occurring in these systems. They also radiate intensely, you could see them from halfway across the universe. There’s a need to know the basic plasma physics in these conditions if you want to interpret observations of those systems. A lot of my work involves doing plasma simulations of turbulence in these extreme parameter regimes.
What are one or two research projects you’ll focus on the most first?
One of them is on making reduced models of plasmas by using non-equilibrium statistical mechanical ideas. Statistical mechanics is one of the core subjects of physics, but it doesn’t really seem to apply to plasmas very often. This is because a lot of plasmas are in this regime that’s called collisionless plasma, where they are knocked out of thermal equilibrium, and then they always exist in a non-thermal state. That’s not what standard statistical mechanics is applicable to. This is one of the problems that I’m studying, whether there is some theoretical framework to study these non-equilibrium plasmas, to understand basic things like: what does it mean for entropy to be produced in these types of plasmas? The important application of this work is to explain how are particles accelerated to really high energies in plasmas. The particle acceleration process is important for explaining cosmic rays which are bombarding the Earth, and then also explaining the highest energy radiation which we see from those systems.
Another thing I’m thinking about these days is plasmas near black holes. In the center of the Milky Way, for example, there’s a supermassive black hole called Sagittarius A*, which was recently imaged a year or two ago by the Event Horizon Telescope. It’s a very famous picture. What you see is the shape of the black hole and then all the plasma in the vicinity, which is in the accretion disk. I’m trying to understand the properties of that turbulent plasma and how to model the type of radiation coming out of the system. And then also whether we should expect neutrinos to be coming out, because you would need to get very high energy protons in order to produce neutrinos. And it’s still an open question of whether or not that happens in these systems.
What attracted you to UW–Madison?
It’s just a perfect match in many ways. It really feels like a place where I’m confident that I could succeed and accomplish my goals, be an effective mentor, and build a successful group. It has all the resources I need, it has the community I need as a plasma physicist to interact with. I think it has a lot to offer to me and likewise, I have a lot to offer to the department there. I’m also really looking forward to the farmers’ market and cheese and things like that. You know, just the culture there.
What is your favorite element and/or elementary particle?
I like the muon. It is just a heavy version of the electron, I don’t remember, something like 100 times more massive or so. It’s funny that such particles exist and this is like the simplest example of one of those fundamental particles which we aren’t really familiar with, it’s just…out there. You could imagine situations where you just replace electron with a muon and then you get slightly different physics out of it.
What hobbies and interests do you have?
They change all the time. But some things I’ve always done: I like running, skiing, bouldering indoors, disk golf, racquet sports, and hiking. (Cross country or downhill skiing?) It’s honestly hard to choose which one I prefer more. In Wisconsin, definitely cross country. If I’m in real mountains, the Alps or the Rockies, then downhill is just an amazing experience.
