The largest magnetic fields in galaxy clusters have been revealed for the first time

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.

a 3-panel picture. The left half is a blue swirly image titled "El Gordo galaxy cluster" and labeled "radius: 6M light years." A tiny square inset of this left picture is enlarged in the top right, titled "fishhook galaxy", which is a hook-shaped orange swirl of gas-like substance. the bottom right panel is the Milky Way for comparison, with a radius of 52,850 light years
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.

UW physicists part of study offering unique insights into the expansion of the universe

This post is modified from one originally published by Fermilab

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.

a mostly-black background of space with dots of various sized stars across the image. The title reads "Dark Energy Camera Deep Image" and has a square inset of a swirly, wispy image, which is enlarged in the inset and labeled "supernova"
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.

profile photo of keith bechtol
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.”

For the full story, please see the Fermilab news release

Physics PhD student Stephen McKay named ALMA ambassador

profile photo of Stephen McKay
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.”

a series of dish antenna telescopes is gently illuminated under the night sky with the milky way galaxy visible above
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

This story was originally posted by the Graduate School

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.

profile picture of Jimena Gonzalez
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.

“Sandwich” structure found to reduce errors caused by quasiparticles in superconducting qubits

Qubits are notoriously more prone to error than their classical counterparts. While superconducting quantum computers currently use on the order of 100 to 1000 qubits, an estimated one million qubits will be needed to track and correct errors in a quantum computer designed for real-world applications. At present, it is not known how to scale superconducting qubit circuits to this size.

In a new study published in PRX Quantum, UW–Madison physicists from Robert McDermott’s group developed and tested a new superconducting qubit architecture that is potentially more scalable than the current state of the art. Control of the qubits is achieved via “Single Flux Quantum” (SFQ) pulses that can be generated close to the qubit chip. They found that SFQ-based control fidelity improved ten-fold over their previous versions, providing a promising platform for scaling up the number of qubits in a quantum array.

profile photo of Robert McDermott
Robert McDermott
profile photo of Vincent Liu
Vincent Liu

The architecture involves a sandwich of two chips: one chip houses the qubits, while the other contains the SFQ control unit. The new approach suppresses the generation of quasiparticles, which are disruptions in the superconducting ground state that degrade qubit performance.

“This structure physically separates the two units, and quasiparticles on the SFQ chip cannot diffuse to the quantum chip and generate errors,” explains Chuan-Hong Liu, PhD ’23, a former UW–Madison physics graduate student and lead author of the study. “This design is totally new, and it greatly improves our gate fidelities.”

Liu and his colleagues assessed the fidelity of SFQ-based gates through randomized benchmarking. In this approach, the team established operating parameters to maximize the overall fidelity of complex control sequences. For instance, for a qubit that begins in the ground state, they performed long sequences incorporating many gates that should be equivalent to an identity operation; in the end, they measured the fraction of the population remaining in the ground state. A higher measured ground state population indicated higher gate fidelity.

Inevitably, there are residual errors, but the reduced quasiparticle poisoning was expected to lower the error rate and improve gate fidelities — and it did.

four panels showing the new chip architecture. The two on the left just show the two computer chips, and then the top right panel shows them "sandwiched" on top of each other. The bottom right panel is a circuit diagram of the whole setup.
The quantum-classical multichip module (MCM). (a) A micrograph of the qubit chip. (b) A micrograph of the SFQ driver chip. (c) A photograph showing the assembled MCM stack; the qubit chip is outlined in red and the SFQ chip is outlined in blue. (d) The circuit diagram for one qubit-SFQ pair. | From Liu et al, PRX Quantum.

“Most of the gates had 99% fidelity,” Liu says. “That’s a one order of magnitude reduction in infidelity compared to the last generation.”

Importantly, they showed the stability of the SFQ-based gates over the course of a six-hour experimental run.

Later in the study, the researchers investigated the source of the remaining errors. They found that the SFQ unit was emitting photons with sufficient energy to create quasiparticles on the qubit chip. With the unique source of the error identified, Liu and his colleagues can develop ways to improve the design.

“We realized this quasiparticle generation is due to spurious antenna coupling between the SFQ units and the qubit units,” Liu says. “This is really interesting because we usually talk about qubits in the range of one to ten gigahertz, but this error is in the 100 to 1000 gigahertz range. This is an area people have never explored, and we provide a straightforward way to make improvements.”

This study is a collaboration between the National Institute of Standards and Technology, Syracuse University, Lawrence Livermore National Laboratory, and UW–Madison.

This work was funded in part by the National Science Foundation (DMR-1747426); the Wisconsin Alumni Research Foundation (WARF) Accelerator; Office of the Director of National Intelligence, Intelligence Advanced Research Projects Activity (IARPA-20001-D2022-2203120004); and the NIST Program on Scalable Superconducting Computing and the National Nuclear Security Administration Advanced Simulation and Computing Beyond Moore’s Law program (LLNL-ABS-795437).

Physics has three winners in the Cool Science Image contest!

The winners of the UW–Madison 13th annual Cool Science Image contest were announced, and Physics has three winners! Our winners include graduate student Jacob Scott, the graduate student-professor pairing of Jimena González and Keith Bechtol, and alum Aedan Gardill, PhD ’23. Their winning images are below.

A panel of experienced artists, scientists and science communicators chose 12 winning images based on the aesthetic, creative and scientific qualities that distinguished them from scores of entries. The winning entries showcase the research, innovation, scholarship and curiosity of the UW–Madison community through visual representations of socioeconomic strata, brain cells snuffed out in Parkinson’s disease, the tangle of technology required to equip a quantum computing lab and a bug-eyed frog that opened students’ eyes to the world.

The winning images go on display this week in an exhibit at the McPherson Eye Research Institute’s Mandelbaum and Albert Family Vision Gallery on the ninth floor of the Wisconsin Institutes for Medical Research, 111 Highland Ave. The exhibit, which runs through the end of 2023, opens with a public reception at the gallery Thursday, Sept. 28, from 4:30 to 6:30 p.m. The exhibit also includes historical images of UW science, in celebration of the 175th anniversary of the University of Wisconsin’s founding.

The Cool Science Image Contest recognizes the technical and creative skills required to capture and create images, videos and other media that reveal something about science or nature while also leaving an impression with their beauty or ability to induce wonder. The contest is sponsored by Madison’s Promega Corp., with additional support from UW–Madison’s Office of University Communications.

a photograph of a room with the lights off, but the bulk of the image is taken up by a large piece of complicated equipment with many different colored laser lights visible, illuminating the shape of the equipment
The glow of red and green lasers and an array of supporting electronics fill a UW–Madison lab where physicists study the behavior of cesium atoms cooled within a fraction of a degree of absolute zero. The atoms could be used to store information in quantum computing systems. | Jacob Scott
an oddly-shaded portrait of physicist Marie Curie, which can only be viewed when a light polarizer is held in front of the portrait
Like the radiation she studied, this portrait of physicist Marie Curie is invisible until revealed by the proper equipment — in this case, a polarizer, a filter that blocks all light waves except those oscillating in a certain direction. One polarizing filter on the back layer of the portrait organizes the light shining through to the viewer. That light passes through layers of colorless cellophane, which rotate the waves a little or a lot depending on the layer’s thickness. A second polarizing filter, held by the viewer, filters the light again, selecting light at the wavelengths that correspond to the intended colors of the portrait. The image above is as the portrait appears viewed through a polarizer. | Aedan Gardill PhD ’23
an array of red-glowing images on a dark black background
Each image in this collage is of an astronomical phenomenon known as a strong gravitational lens, in which the light from a galaxy or cluster of galaxies is curved by a massive object in the foreground. The light is distorted into bright arcs, exhibiting physics theorized by Albert Einstein. Strong gravitational lenses offer a way to study dark matter, difficult to detect but considered a crucial factor in the structure, evolution and fate of the cosmos. | Jimena González and Keith Bechtol

Jimena González wins 2023 OSG David Swanson Award

Early in her thesis research, Jimena González was waiting. A lot.

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.

a woman stands in front of a screen with a research slide on the screen, she faces the audience and is gesturing with her hands.
Jimena González presents an award lecture at the 2023 Throughput Computing Conference. (provided by Jimena González)

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.”

This summer, González was selected as one of two recipients of the OSG David Swanson Award.

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.”

Zain Abhari selected for SACLA graduate internship

a woman stands in front of a tree with a Japanese castle in the near background
Zain Abhari on a tour at Himeji Castle, which is one of the last few fully intact castles in Japan and is located near the SACLA facility | Photo provided by Zain Abhari

Congrats to Physics PhD student Zain Abhari for being selected to the SACLA Research Support Program for Graduate Students. The one-year internship run by SACLA (the SPring-8 Angstrom Compact free electron LAser) accepts graduate students with a demonstrated interest in using X-ray free electron lasers (XFELs) for their research and provides them with training and beam time at the facility in Japan.

Prior to her acceptance in the program, Abhari had already spent time at SACLA as part of her research in Uwe Bergmann’s group. While there, her collaborator told her about the program and recommended she apply.

“My goal after the PhD is to work at one of these large-scale facilities, specifically the X-ray free electron lasers and there’s only six of them right now in the world,” Abhari says. “If I can get my foot in the door in Japan, or get the experience to then help me with any of the other ones, that would be pretty awesome.”

Abhari was also interested in the program because SACLA’s laser aligns well with the goals of her thesis research, which is to obtain intense, stable XFEL pulses to apply to different spectroscopy techniques. For about the past decade, XFEL has allowed researchers to make ultrafast movies of molecular changes, essentially helping them to see chemical reactions take place. But x-ray lasers are “dirty,” and they contain multiple wavelengths of light of varying intensity. Last year, Bergmann and his colleagues somewhat accidentally discovered a way to make the pulses cleaner through two intense, femtosecond-spaced pulses.

Even though the researchers think they know how the useful pulses work, producing and controlling them are a completely different story — and one that Abhari hopes to unravel in her research.

“Right now, they’re just random,” Abhari says. “So the goal is to understand them. And then if we understand them, can we control them? If we can control them, can we apply them?”

Abhari will travel to Japan for three months beginning in September, where the program provides on-campus housing and time on the laser. Without the access she is now granted by this internship, her research would have been much more focused on short rounds of data collection followed by off-site data analysis.

“Now, I can get my hands on the laser and collect data to try to understand parameters that allow us to get the specific output we’re looking for,” Abhari says. “I have data that allude me to what those parameters will be, but now in real time, I can be like, ‘If I do this, I see this; if I do that, I see that.’”

In addition to her thesis research, Abhari will be working with her SACLA collaborators on a machine learning project to optimize beam focusing, and helping learn about and improve a portable beam nanofocusing apparatus.

 

Physics students earn 2023 NSF graduate fellowships

Congrats to current Physics PhD students Samuel Hori and Alysa Rogers and undergraduate Emil Pellett on earning 2023 National Science Foundation Graduate Research Fellowships! Congrats also to PhD student Spencer Weeden for earning an honorable mention!

The Graduate Research Fellowship Program (GRFP) supports high-potential scientists and engineers in the early stages of their careers. Each year, more than 12,000 applicants compete for ~2,000 fellowship awards. NSF GRFP awards are highly sought and competitive. The fellowship is awarded to individuals in the early stages of their graduate study, who intend to pursue research-based graduate studies in science, technology, engineering, and mathematics (STEM).

The program provides awardees with three years of financial support consisting of a $37,000 annual stipend and a $12,000 education allowance. UW–Madison contributes toward fringe benefits.

UW–Madison researchers key in search for neutrino emission from the brightest gamma-ray burst ever detected

This story was originally published by WIPAC

On October 9th, 2022, an unusually bright pulse of high-energy radiation whizzed past Earth, captivating astronomers around the world. The luminous emission came from a gamma-ray burst (GRB), one of the most powerful classes of explosions in the universe. Named GRB 221009A, it triggered detectors at NASA’s Gamma-ray Burst Monitor and Large Area Telescope (both on board the Fermi Gamma-ray Space Telescope), the Neil Gehrels Swift Observatory, and the Wind spacecraft as well as other telescopes that quickly turned to the GRB site to study its aftermath.

profile photo of Jessie Thwaites
Jessie Thwaites

This record-shattering GRB is one of the closest and the brightest GRB ever spotted, earning it the nickname BOAT (“brightest of all time”). This GRB is believed to come from an exploding star and likely signals the birth of a black hole.

In a new study by the IceCube Collaboration, published today in The Astrophysical Journal Letters, UW–Madison researchers presented results of one of five searches for neutrino emission from GRB 221009A that leveraged the full detector range, covering nine orders of magnitude in energy. Because no significant emission was found across samples spanning 10 MeV to 10 PeV, the results are the most stringent constraints on neutrino emission from GRBs.

As some of the most energetic sources in the universe, GRBs have long been considered a possible astrophysical source of neutrinos—tiny “ghostlike” particles that travel through space and large amounts of matter unhindered. These high-energy neutrinos are of particular interest to the National Science Foundation-supported IceCube Neutrino Observatory, a gigaton-scale neutrino detector at the South Pole.

IceCube is run by the international IceCube Collaboration, which comprises over 350 scientists from 58 institutions around the world. The Wisconsin IceCube Particle Astrophysics Center (WIPAC), a research center at UW–Madison, is the lead institution for the IceCube project.

Previously, IceCube has performed searches for neutrino emission from GRBs, but thus far, a correlation has not been found between high-energy neutrinos and GRBs. The recent observation of GRB 221009A presented IceCube with the best opportunity yet to search for neutrino emission by GRBs.

profile photo of Justin Vandenbroucke
Justin Vandenbroucke

“Not only was this GRB the brightest ever detected in gamma rays, it also occurred in a region of the sky where IceCube is very sensitive,” says UW–Madison physics professor Justin Vandenbroucke, who helped lead the analysis.

For the study, collaborators carried out five complementary IceCube analyses that encompassed the full energy range of the detector. Each analysis targeted a specific energy range, with the idea of covering as wide an energy range as possible. UW–Madison physics PhD student Jessie Thwaites was one of the main analyzers.

Thwaites performed a “fast response” analysis based on real-time data from the South Pole to search for high-energy (0.10 teraelectronvolts to 10 petaelectronvolts) neutrinos from the direction of the GRB. They chose two time windows: one three-hour window covering all of the triggers reported in real time, and one covering two days. Their analysis, which set strong constraints on neutrino emission from GRBs, was quickly reported to the community, within hours of the GRB being detected by the gamma-ray satellites.

“In the high energies, our upper limits are very constraining—they are below the observations from gamma-ray telescopes,” says Thwaites. “These upper limits, combined with the observations from many electromagnetic telescopes, give us more information about GRBs as potential particle accelerators.”

Because this GRB is so bright, and because it has been so well studied, IceCube is able to place constraining upper limits on neutrino emission models proposed for this specific GRB. These constraints will enable better understanding of how GRBs work.

The collaborators are already developing new methods to improve searches for neutrinos from GRBs and other transient astrophysical sources. In addition, future upgrades and proposed extensions of IceCube, including the IceCube Upgrade project and IceCube-Gen2, could be the key to finding high-energy neutrino emission from GRBs or other transients.

According to Vandenbroucke, “This GRB illustrates the capabilities of IceCube for real-time follow-up of astrophysical transients. IceCube views the entire sky, all the time, over a factor of a billion in energy range. There is likely a burst of neutrinos already flying towards us from some other cosmic source, and we are ready for it.”

+ info “Limits on Neutrino Emission from GRB 221009A from MeV to PeV using the IceCube Neutrino Observatory,” The IceCube Collaboration: R. Abbasi et al. Published in The Astrophysical Journal Letters. arxiv.org/abs/2302.05459