astrophysics

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.

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.

Ke Fang earns NSF CAREER award

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profile photo of Ke Fang
Ke Fang

Congrats to Ke Fang, assistant professor of physics, WIPAC faculty member, and HAWC spokesperson, on earning an NSF CAREER award! CAREER awards are NSF’s most prestigious awards in support of early-career faculty who have the potential to serve as academic role models in research and education and to lead advances in the mission of their department or organization.

Fang’s award is sponsored by the NSF Windows on the Universe: Multimessenger Astrophysics program. In multimessenger astrophysics, scientists search for multiple high energy signals to identify their sources and learn more about the makeup of our universe. WIPAC hosts both the IceCube neutrino telescope and the HAWC gamma ray telescope, and Fang says she is excited to have access to high-quality data from both. In her NSF proposal, she plans to use that data in two ways.

“One is evolving novel data analysis techniques to study the problems that remain outstanding, such as the source of high-energy neutrinos,” Fang says. “The second part is once we have these data analysis results, then we’ll use numerical simulations to understand our observations.”

In addition to an innovative research component, NSF proposals require that the research has broader societal impacts, such as working toward greater inclusion in STEM or increasing public understanding of science. Once again, Fang finds herself well-positioned at WIPAC, where the outreach team has developed Master Classes, a one-day event where high school students come to WIPAC, spend time with scientists, and learn about topics not typically covered in high school physics class. Currently, the students learn about IceCube’s instrumentation and how to analyze the complex detector data.

“The course is already well designed, but from my perspective, I use a lot of numerical simulation in my research, so one thing I proposed to do is that I would design a module that would incorporate some of these modern numerical study techniques into the master class,” Fang says. “The students will now learn how to study physics using supercomputers, using numerical simulations.”

UW–Madison physicists key in revealing neutrinos emanating from galactic neighbor with a gigantic black hole

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On Earth, billions of subatomic particles called neutrinos pass through us every second, but we never notice because they rarely interact with matter. Because of this, neutrinos can travel straight paths over vast distances unimpeded, carrying information about their cosmic origins.

Although most of these aptly named “ghost” particles detected on Earth originate from the Sun or our own atmosphere, some neutrinos come from the cosmos, far beyond our galaxy. These neutrinos, called astrophysical neutrinos, can provide valuable insight into some of the most powerful objects in the universe.

For the first time, an international team of scientists has found evidence of high-energy astrophysical neutrinos emanating from the galaxy NGC 1068 in the constellation Cetus.

The detection was made by the National Science Foundation-supported IceCube Neutrino Observatory, a 1-billion-ton neutrino telescope made of scientific instruments and ice situated 1.5-2.5 kilometers below the surface at the South Pole.

These new results, to be published tomorrow (Nov. 4, 2022) in Science, were shared in a presentation given today at the Wisconsin Institute for Discovery.

“One neutrino can single out a source. But only an observation with multiple neutrinos will reveal the obscured core of the most energetic cosmic objects,” says Francis Halzen, a University of Wisconsin–Madison professor of physics and principal investigator of the IceCube project. “IceCube has accumulated some 80 neutrinos of teraelectronvolt energy from NGC 1068, which are not yet enough to answer all our questions, but they definitely are the next big step toward the realization of neutrino astronomy.”

For the full story, please visit https://news.wisc.edu/uw-madison-scientists-and-staff-key-in-revealing-neutrinos-emanating-from-galactic-neighbor-with-a-gigantic-black-hole/

 

Study led by UW–Madison researcher confirms star wreck as source of extreme cosmic particles

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Astronomers have long sought the launch sites for some of the highest energy protons in our galaxy. Now, a study using 12 years of data from NASA’s Fermi Gamma-ray Space Telescope (Fermi) confirms that a remnant of a supernova, or star explosion, is just such a place, solving a decade-long cosmic mystery.

a mostly black image of space, with some small white-ish out-of-focus stars, and a large fuzzy pink blob partially overlapping a green-hued amorphous apparition
The newly discovered PeVatron (in pink) is hosted by a supernova remnant (in green) called G106.3+2.7. The supernova remnant is believed to have formed together with the pulsar (in magenta) about 10,000 years ago. Particles accelerated by the shock waves of the supernova remnant interact with the gas in the interstellar medium, producing high-energy gamma-ray emission. Credit: Jayanne English, University of Manitoba, NASA/Fermi/Fang et al. 2022, and Canadian Galactic Plane Survey/DRAO.

Previously, Fermi has shown that the shock waves of exploded stars boost particles to speeds comparable to that of light. Called cosmic rays, these particles mostly take the form of protons, but can include atomic nuclei and electrons. Because they all carry an electric charge, their paths become scrambled as they whisk through our galaxy’s magnetic field, which masks their origins. But when these particles collide with interstellar gas near the supernova remnant (SNR), they produce a telltale glow in gamma rays—the highest-energy light there is.

“Theorists think the highest energy cosmic ray protons in the Milky Way reach a million billion electron volts, or PeV energies,” said Ke Fang, an assistant professor of physics at the Wisconsin IceCube Particle Astrophysics Center (WIPAC), a research center at the University of Wisconsin–Madison. “The precise nature of their sources, which we call PeVatrons, has been difficult to pin down.”

Fang, who led the study, performed the data analysis and developed the theory models. The research team identified a few suspected PeVatrons, including one at the center of our galaxy. Naturally, SNR top the list of candidates. Yet out of about 300 known remnants, only a few have been found to emit gamma rays with sufficiently high energies.

Read the full story

Massive bubbles at center of Milky Way caused by supermassive black hole

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depiction of a blueish circle and its reflection below seen in distant space with a Milky Way image in the background
The enormous clouds of material known as the eRosita and Fermi bubbles extend above and below the galactic plane of the Milky Way. NASA/KAREN YANG/MATEUSZ RUSZKOWSKI/ELLEN ZWEIBEL

New research reveals the origins of enormous bubbles of material emanating from the center of the Milky Way.

The related structures — known as the eRosita and Fermi bubbles and the microwave haze — are the result of a powerful jet of activity from the supermassive black hole at the center of the galaxy. The study, published March 7 in Nature Astronomy, also shows the jet began spewing out material about 2.6 million years ago, and lasted about 100,000 years.

profile photo of Ellen Zweibel
Ellen Zweibel

The work was led by Karen Yang of National Tsing Hua University in Taiwan with University of Wisconsin–Madison astronomer Ellen Zweibel and Mateusz Ruszkowski at the University of Michigan.

The black hole origin of these huge bubbles rules out an alternative model that the expansion of the material was driven by exploding stars. Such a nuclear starburst would last about 10 million years, according to Zweibel, a professor of astronomy and physics at UW–Madison.

“On the other hand, our active black hole model accurately predicts the relative sizes of the eRosita X-ray bubbles and the Fermi gamma ray bubbles, provided the energy injection time is about one percent of that, or one-tenth of a million years,” Zweibel says. “Injecting energy over 10 million years would produce bubbles with a completely different appearance. While both the black hole and stellar explosion models were in reasonably good agreement with the gamma ray data, it’s the discovery of the X-ray bubbles, and the opportunity to compare the X-ray and gamma ray bubbles, which provide the crucial, previously missing piece.”

The enormous structures are nearly 36,000 light-years tall, one-third the diameter of the Milky Way. The eRostia and Fermi bubbles were named for the telescopes that discovered them in 2020 and 2010, respectively.

Read more about the discovery at the University of Michigan’s website and from the study’s lead author.

IceCube to appear in BBC and PBS documentaries

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This story was originally published by IceCube.

The IceCube Neutrino Observatory, a massive astroparticle physics experiment located at the South Pole, will be featured in two upcoming documentaries about neutrinos produced for the BBC and PBS NOVA.

Sometimes called the world’s biggest and strangest telescope, IceCube comprises over 5,000 light sensors deployed in a cubic kilometer of ice at the South Pole. Despite its inhospitable environment, the South Pole’s abundance of ice makes it an ideal location for detecting neutrinos: tiny fundamental particles that could reveal unseen parts of the universe.

For these documentaries, IceCube staff from the experiment’s headquarters at the Wisconsin IceCube Particle Astrophysics Center (WIPAC), a research center of the University of Wisconsin–Madison, captured video footage at the South Pole. During the austral summer of 2019, Kael Hanson, John Hardin, Matt Kauer, John Kelley, and Yuya Makino recorded video at the bottom of the world as they conducted annual maintenance and other work on the observatory. The footage was then sent “up north” for use in the two different documentaries.

The BBC documentary, “Neutrino: Hunting the Ghost Particle,” will premiere on BBC Four on Wednesday, September 22 from 9:00 – 10:00 pm BST. It is described as “an astonishing tale of perseverance and ingenuity that reveals how scientists have battled against the odds for almost a century to detect and decode the neutrino, the smallest and strangest particle of matter in the universe.” The documentary will feature footage and interviews from IceCube and will discuss the experiment’s role in neutrino astronomy.

PBS NOVA will feature IceCube and its science in its “Particles Unknown” documentary premiering on Wednesday, October 6 at 9:00 pm CDT. IceCube will appear near the end of the program, which is also about the hunt for neutrinos, “the universe’s most common—yet most elusive and baffling—particle,” and includes an interview with Hanson, who is also IceCube’s director of operations and the director of WIPAC.

Learn more about IceCube and neutrinos at IceCube’s website.

The IceCube Neutrino Observatory is funded primarily by the National Science Foundation (OPP-1600823 and PHY-1913607) and is headquartered at the Wisconsin IceCube Particle Astrophysics Center, a research center of UW–Madison in the United States. IceCube’s research efforts, including critical contributions to the detector operation, are funded by agencies in Australia, Belgium, Canada, Denmark, Germany, Japan, New Zealand, Republic of Korea, Sweden, Switzerland, the United Kingdom, and the United States. The IceCube EPSCoR Initiative (IEI) also receives additional support through NSF-EPSCoR-2019597. IceCube construction was also funded with significant contributions from the National Fund for Scientific Research (FNRS & FWO) in Belgium; the Federal Ministry of Education and Research (BMBF) and the German Research Foundation (DFG) in Germany; the Knut and Alice Wallenberg Foundation, the Swedish Polar Research Secretariat, and the Swedish Research Council in Sweden; and the University of Wisconsin–Madison Research Fund in the U.S.

 

Balantekin named co-PI on NSF grant to solve cosmic mystery

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This story has been modified from one originally published by New York Institute of Technology. 

A team of University of Wisconsin–Madison and New York Institute of Technology physicists has secured a grant from the National Science Foundation (NSF) in an attempt to solve one of science’s greatest mysteries: how the universe formed from stardust.

Many of the universe’s elements, including the calcium found in human bones and iron in skyscrapers, originated from ancient stars. However, scientists have long sought to understand the cosmic processes that formed other elements—those with undetermined origins. Now, UW–Madison professor of physics Baha Balantekin and co-principal investigator Eve Armstrong assistant professor of physics at New York Institute of Technology, will perform the first known research project that uses weather prediction techniques to explain these events. Their revolutionary work will be funded by a two-year $299,998 NSF EAGER grant, an award that supports early-stage exploratory projects on untested but potentially transformative ideas that could be considered “high risk/high payoff.”

While the Big Bang created the first and lightest elements (hydrogen and helium), the next and heavier elements (up to iron on the periodic table) formed later inside ancient, massive stars. When these stars exploded, their matter catapulted into space, seeding that space with elements. Eventually, stardust matter from these supernovae formed the sun and planets, and over billions of years, Earth’s matter coalesced into the first life forms. However, the origins of elements heavier than iron, such as gold and copper, remain unknown. While they may have formed during a supernova explosion, current computational techniques render it difficult to comprehensively study the physics of these events. In addition, supernovae are rare, occurring about once every 50 years, and the only existing data is from the last explosion in 1987.

Large information-rich data sets are obtained from increasingly sophisticated experiments and observations on complicated nonlinear systems. The techniques of Statistical Data Assimilation (SDA) have been developed to handle very nonlinear systems with sparsely sampled data. SDA techniques, akin to the path integral methods commonly used in physics, are used in fields ranging from weather prediction to neurobiology. Armstrong and Balantekin will apply the SDA methods to the vast amount of data accumulated so far in neutrino physics and astrophysics.

With simulated data, in preparation for the next supernova event, the team will use data assimilation to predict whether the supernova environment could have given rise to some heavy elements. If successful, these “forecasts” may allow scientists to determine which elements formed from supernova stardust.

This project will provide an opportunity to the Physics graduate students interested in neutrinos to master an interdisciplinary technique with many other applications.

“Physicists have sought for years to understand how, in seconds, giant stars exploded and created the substances that led to our existence. A technique from another scientific field, meteorology, may help to explain an important piece of this puzzle that traditional tools render difficult to access,” says Armstrong.

The NSF is an independent agency of the U.S. government that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National Institutes of Health. NSF funding accounts for approximately 27 percent of the total federal budget for basic research conducted at U.S. colleges and universities.

This project is funded by NSF EAGER Award ID No. 2139004. 

The content is solely the responsibility of the authors and does not necessarily represent the official views of the NSF.

Magnetic fields implicated in the mysterious midlife crisis of stars

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a brightly colored sun with a cutout showing into the core, with lines suggesting the spinning motion
Artist’s impression of the spinning interior of a star, generating the stellar magnetic field. This image combines a dynamo simulation of the Sun’s interior with observations of the Sun’s outer atmosphere, where storms and plasma winds are generated. | Credit:
CESSI / IISER Kolkata / NASA-SVS / ESA / SOHO-LASCO

This post was originally published by the Royal Astronomical Society. UW–Madison physics graduate student Bindesh Tripathi is the lead author of the scientific publication.

Middle-aged stars can experience their own kind of midlife crisis, experiencing dramatic breaks in their activity and rotation rates at about the same age as our Sun, according to new research published today in Monthly Notices of the Royal Astronomical Society: Letters. The study provides a new theoretical underpinning for the unexplained breakdown of established techniques for measuring ages of stars past their middle age, and the transition of solar-like stars to a magnetically inactive future.

Astronomers have long known that stars experience a process known as ‘magnetic braking’: a steady stream of charged particles, known as the solar wind, escapes from the star over time, carrying away small amounts of the star’s angular momentum. This slow drain causes stars like our Sun to gradually slow down their rotation over billions of years.

In turn, the slower rotation leads to altered magnetic fields and less stellar activity – the numbers of sunspots, flares, outbursts, and similar phenomena in the atmospheres of stars, which are intrinsically linked to the strengths of their magnetic fields.

profile photo of Bindesh Tripathy
Bindesh Tripathi

This decrease in activity and rotation rate over time is expected to be smooth and predictable because of the gradual loss of angular momentum. The idea gave birth to the tool known as ‘stellar gyrochronology’, which has been widely used over the past two decades to estimate the age of a star from its rotation period.

However recent observations indicate that this intimate relationship breaks down around middle age. The new work, carried out by Bindesh Tripathi at UW–Madison and the Indian Institute of Science Education and Research (IISER) Kolkata, India, provides a novel explanation for this mysterious ailment. Prof. Dibyendu Nandy, and Prof. Soumitro Banerjee of IISER are co-authors.

Using dynamo models of magnetic field generation in stars, the team show that at about the age of the Sun the magnetic field generation mechanism of stars suddenly becomes sub-critical or less efficient. This allows stars to exist in two distinct activity states – a low activity mode and an active mode. A middle aged star like the Sun can often switch to the low activity mode resulting in drastically reduced angular momentum losses by magnetized stellar winds.

Prof. Nandy comments: “This hypothesis of sub-critical magnetic dynamos of solar-like stars provides a self-consistent, unifying physical basis for a diversity of solar-stellar phenomena, such as why stars beyond their midlife do not spin down as fast as in their youth, the breakdown of stellar gyrochronology relations, and recent findings suggesting that the Sun may be transitioning to a magnetically inactive future.”

The new work provides key insights into the existence of low activity episodes in the recent history of the Sun known as grand minima – when hardly any sunspots are seen. The best known of these is perhaps the Maunder Minimum around 1645 to 1715, when very few sunspots were observed.

The team hope that it will also shed light on recent observations indicating that the Sun is comparatively inactive, with crucial implications for the potential long-term future of our own stellar neighbor.

Celebrating IceCube’s first decade of discovery

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It was the beginning of a grand experiment unlike anything the world had ever seen. Ten years ago today, the IceCube Neutrino Observatory fully opened its eyes for the first time.

Over the course of the previous seven years, dozens of intrepid technicians, engineers, and scientists had traveled to the South Pole—one of the coldest, driest, and most isolated places on Earth—to build the biggest, strangest telescope in the world. Crews drilled 86 holes nearly two-and-a-half kilometers deep and lowered a cable strung with 60 basketball-sized light detectors into each hole. The result was a hexagonal grid of sensors embedded in a cubic kilometer of ice about a mile below the surface of the Antarctic ice sheet. On December 18, 2010, the 5,160th light sensor was deployed in the ice, completing the construction of the IceCube Neutrino Observatory.

The purpose of the unconventional telescope was to detect signals from passing astrophysical neutrinos: mysterious, tiny, extremely lightweight particles created by some of the most energetic and distant phenomena in the cosmos. IceCube’s founders believed that studying these astrophysical neutrinos would reveal hidden parts of the universe. Over the course of the next decade, they would be proven right.

IceCube began full operations on May 13, 2011 — ten years ago today — when the detector took its first set of data as a completed instrument. Since then, IceCube has been watching the cosmos and collecting data continuously for a decade.

During its first few years of operation, IceCube accumulated vast amounts of data, but it wasn’t until 2013 that the observatory yielded its first major results.

For the full story, please visit https://icecube.wisc.edu/news/collaboration/2021/05/celebrating-icecubes-first-decade-of-discovery/

Ellen Zweibel elected to the National Academy of Sciences

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Ellen Zweibel

Astronomy and physics Professor Ellen Zweibel has been honored with membership in the National Academy of Sciences.

Zweibel is among 120 new members — and one of 59 women, the largest group ever — elected to the academy, one of the highest honors that can be conferred on an American scientist. Members are chosen “in recognition of their distinguished and continuing achievements in original research.”

Zweibel, the W.L. Kraushaar Professor of Astronomy and Physics, came to UW–Madison in 2003. She studies the way magnetic fields shape the universe, including the physics of plasmas in stars and galaxies and the cosmic rays they throw out into the universe.

A founding member of the Center for Magnetic Self-Organization, a Physics Frontier Center funded by the National Science Foundation and the U.S. Department of Energy, Zweibel won the American Physical Society’s Maxwell Prize for Plasma Physics in 2016.

The National Academy of Sciences — with the National Academy of Engineering and the National Academy of Medicine — provides science, engineering, and health policy advice to the federal government and other organizations. It is a private, nonprofit institution established in 1863 under a congressional charter signed by President Abraham Lincoln.

For the full story, please visit https://news.wisc.edu/national-academy-of-sciences-adds-two-uw-madison-faculty-members/