SPACE/COSMOS
We can predict space weather. What if we could also stop it?
Solar flares and geomagnetic storms can kill satellites and mess with GPS. A Boston University researcher has designed a space-based system to better protect us from rogue interplanetary weather
The weather on Earth can get pretty messy sometimes. But in space, it can be wild—and the effects can be far-reaching.
Solar flares, giant explosions on the sun, can send out streams of energy that block radio communications and fry satellite electronics. Geomagnetic storms, caused by variations in solar wind, can mess with GPS signals and spark current surges on Earth that overload power grids.
The impact of space weather isn’t limited to temporarily losing electricity or digging out dusty paper maps for directions when satellite navigation systems fail. Every electronic financial transaction in the world, for instance, relies on time stamps sent by satellite systems. And, in May 2024, a solar storm threw out GPS systems used to accurately guide tractors in planting and harvesting crops, hobbling food production for days and costing US farmers $500 million.
Although satellites can be built with tougher shields or have their orbits adjusted, those are just Band-Aids; there’s currently little we can do to protect ourselves from space storms.
Boston University researcher Brian Walsh has an idea for how to change that. He’s been testing the theoretical feasibility of a system of spacecraft that could fire chemical elements to the edge of Earth’s magnetic field, temporarily fortifying our defenses and deflecting potentially damaging space weather. In simulations, Walsh and researchers from the University of Michigan found the system could cut the intensity of a major geomagnetic storm in half. The findings were published in the journal Space Weather.
“Since humans have been in space, we’ve been trying to predict what’s going to happen in the space environment,” says Walsh, a BU College of Engineering associate professor of mechanical engineering. “But we came up with a model that could flip the paradigm. It’s like people in a village who see a river flooding—maybe they can predict when that will happen, but probably what’s even better is if they could build a storm wall. That’s what we’re proposing here.”
Bouncing Storms Past the Earth
Walsh says his idea for a weather wall in space was inspired by a natural phenomenon: material peeling off the Earth’s atmosphere and floating to the edge of our planet’s protective bubble, the magnetosphere, to bolster it. “I thought, maybe you could turn [that process] up, increase the intensity of it,” he says.
His proposed system, named StormWall, would start with the launch of six spacecraft into a geosynchronous orbit matching the Earth’s own rotation. Each craft would be fitted with a canister loaded with what the researchers call a mass-loading material. When released, the material—an alkaline chemical element like barium or lithium—would photoionize, a process that induces an electrical charge, seeding the atmosphere with plasma.
In their simulations, Walsh and his colleagues found that this plasma would disrupt the flow of energy between any solar storm and the magnetosphere—and that would be enough to bounce the space weather around and past our planet.
Not Science Fiction
Walsh admits a weather wall in space sounds a little like science fiction, but says it’s within our reach.
“When you apply some really serious physics to it, it does work. And the amount of mass we need, the launch capacities—it’s all within our capabilities,” he says. “People have always thought, ‘space is huge, the sun is massive, we just have to sit here and take whatever it gives us.’ But what we found is that we can impact it.”
One of the biggest barriers to implementation is cost. Launching six spacecraft, together carrying the equivalent of about a dozen oil trucks–worth of material, wouldn’t be cheap. And once the payload is fired out and photoionizes, the system would be dead and couldn’t be replenished—it’s one and done. But with private companies investing billions in space infrastructure—and even contemplating data centers in orbit—Walsh says the math on cost-benefit ratios could soon favor his proposed approach. In their paper, Walsh and his colleagues point out that a massive once-in-a-century geomagnetic storm—the last one was in 1859—would cause devastating damage in space and on Earth, with power grid costs alone topping $2.4 trillion.
He’s confident the team can bring down the StormWall costs too. Next on their agenda is studying ways to half the material used, simulating a pulsed release of materials to extend the system’s lifespan, and examining potentially more efficient orbits. They also want to dig deeper into the chemistry involved to nail down the best elements to use.
And although space junk is a major issue in Earth’s lower atmosphere, Walsh says any materials they pump into its higher reaches would quickly be carried out of the system after they’ve done their job. “The material drifts out on these natural highways, it leaves the system—the magnetosphere flushes the material out within six or so hours.”
Geoengineering Space
As the head of BU’s Space Physics & Technology Lab, much of Walsh’s broader research is focused on observing and better understanding the space environment around Earth; he and his team were recently part of a mission that sent a telescope to the moon to image our magnetic shield. Although the StormWall project is loosely connected to that wider work, Walsh says it’s a bit of an outlier. “This is quite different than what anyone is doing right now—I don’t know of anyone proposing to geoengineer space.”
Should the idea literally take off, he says that, unlike some space missions that might reap rewards for the few, this one would benefit us all.
“If you built it, if it was deployed, it would help all people on the planet,” says Walsh. “You couldn’t make it in a way that helped only one country, one group of satellites.”
Journal
Space Weather
Method of Research
Computational simulation/modeling
Subject of Research
Not applicable
Article Title
Terrestrial Space Weather Protection Through Human-Produced Mass-Loading
Article Publication Date
2-Jun-2026
Found: Milky Way black hole’s missing wind
The half-century-long search is finally over
image:
This composite image shows evidence for a wind blowing away from Sagittarius A* (Sgr A*), the supermassive black hole in the center of our galaxy. The white dot in the center of the image shows Sgr A*. In orange is data from the Atacama Large Millimeter/Submillimeter Array (ALMA) radio telescopes in Chile, mapping the location of cold gas composed of carbon monoxide in the image. In blue is X-ray data from NASA’s Chandra X-ray Observatory. A large cone-shaped cavity, visible as an absence of cold gas in the ALMA data, is filled by hot X-ray-emitting gas in the Chandra data. Researchers think a hot, energetic wind blowing from Sgr A* created this structure by sweeping the cold gas away or heating it up.
view moreCredit: X-ray: NASA/CXC/Northwestern Univ./M. Gorski; Radio: ESO/NAOJ/NRAO/ALMA; Image processing: NASA/CXC/SAO/K. Arcand and P. Edmonds
The hunt is over.
After more than 50 years of searching, astrophysicists at Northwestern University have finally discovered evidence of a powerful wind blowing from the Milky Way’s central supermassive black hole, Sagittarius A* (Sgr A*).
According to theoretical physics and a long-accepted understanding of galaxies evolution, as black holes consume materials, they should produce wind or jets. Even a small amount of gas falling into a black hole should generate enough energy to push material outwards. Without wind, Sgr A* would be a unique outlier.
But, until now, no one could find it.
By providing the most detailed view yet of how Sgr A* interacts with and transforms its surrounding environment, the scientists resolved one of the longest-standing mysteries in astronomy. It also opens a new window into the physics at play in the center of the Milky Way.
The study will be published on Thursday (June 4) in The Astrophysical Journal Letters.
“Unless a black hole exists in a perfect vacuum, it must blow a wind somehow,” said Northwestern’s Mark Gorski, who co-led the study. “And there is no perfect vacuum in the universe. With new observations, this is the first time we’ve had a clean enough view to see the wind’s imprint. We looked at the data and said, ‘There it is. There is the thing that everybody’s been looking for for 50 years.’”
“We were the first to show that molecular gas very, very close to the black hole is feeding it,” said Elena Murchikova, who co-led the study with Gorski. “The wind is not powerful, and its direction probably wanders with time. It shows that our black hole is not unique, and our place in the universe is not unique.”
Focused on the evolution of galaxies, Gorski is a research assistant professor at Northwestern’s Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). An expert on black hole astrophysics, Murchikova is an assistant professor of physics and astronomy at Northwestern’s Weinberg College of Arts and Sciences and member of CIERA.
Elusive wind at the galaxy’s heart
Although black holes are infamous for swallowing anything that ventures too close, they don’t just pull matter in. They also push material out. For decades, theorists have predicted that all actively feeding black holes launch powerful outflows. As material spirals inward toward a black hole, it moves faster and faster — until it reaches close to the speed of light. This creates enough energy and pressure to fling some of the hot, fast-moving material outward in the form of winds or jets.
While astronomers have spotted evidence of past eruptions from Sgr A*, they struggled to detect currently occurring outflows. The Northwestern team says this is likely because Sgr A* is in a quieter phase and just incredibly difficult to see.
“To observe our own black hole, we have to look through the plane of our galaxy,” Murchikova said. “That means we have to peer through gas, dust and ionized structures, and you can’t really see through all of that easily.”
A cone-shaped cavity
Now, with new tools and observations, the team finally was able to take a closer look. Using five years of extraordinarily deep observations from the Atacama Large Millimeter/Submillimeter Array (ALMA) radio telescopes in Chile, Gorski and Murchikova constructed the sharpest image ever devised of cold molecular gas surrounding the black hole.
The image reflected the gas located incredibly close to Sgr A* — within just one parsec (or about three light-years) of the black hole. Then, the duo applied a calibration method to remove the black hole’s bright radio signals. The resulting image is 100 times deeper and 80 times sharper than previous maps of the region. With this level of detail, it revealed structures that were completely invisible in previous observations.
But one newly revealed, unmistakable feature left Gorski and Murchikova gobsmacked. A vast, cone-shaped cavity — nearly one parsec long and 45 degrees wide — was devoid of cold molecular gas. According to the researchers, only hot, energetic wind blowing from Sgr A* could have created this hollowed-out region. Wherever the hot wind travels, it either sweeps cold gas away or heats it up.
“If you blow hot material from the black hole, it’s not going to want to exist with the cold material,” Gorski said. “It’s either going to push the cold material out or heat it up. And, if it’s too hot, you will no longer see the cold gas.”
Exceptional claims, exceptional evidence
While stars, too, create winds, stellar winds are not powerful enough to carve out a cleanly swept region of this size. Even the combined power of all the nearby stars falls short.
“It’s a huge absence of material,” Gorski said. “We calculated how much energy was needed to create this cavity. It is more than can be provided by the stars in that area. Basically, there has to be input from the supermassive black hole. And, if you follow the shape of the cone, it’s pointed directly at the black hole.”
Before declaring they solved a long-standing mystery, Gorski and Murchikova continued to analyze data to further confirm their results. NASA’s Chandra X-ray Observatory previously pinpointed bright X-ray emissions in the exact same region. In the same location as the bright X-rays, a hollow, cone-shaped region appeared where cold gas was missing.
“Exceptional claims require exceptional evidence,” Gorski said. “We wanted to make sure that we weren’t just looking at some sort of imaging artifact. Then, the X-ray image from Chandra just slotted in perfectly. The molecular features lined up.”
“When you find something that no one has seen before, the first thought that runs through your mind is not ‘Oh my god, we made a discovery,’” Murchikova said. “It’s ‘Oh my god, what’s wrong with my analysis?’ But when we overlaid our image with the X-ray image, it started to make sense.”
A quiet phase of life
Based on how far its effects extend into a nearby stream of ionized gas, the astrophysicists estimate the wind has been active for at least 20,000 years. The discovery also confirms that Sgr A* is relatively quiet compared to other galaxies’ central supermassive black holes.
“The majority of other galaxies spend most of their lives in a state where they are not particularly active,” Murchikova said. “But we can only see them when they are in a fireworks stage. It is very attractive to study black holes when they are in the fireworks stage, but that’s not actually their dominant state. Sgr A* finally gives us a window into the life of a black hole in this quiet state.”
Data from the Atacama Large Millimeter/Submillimeter Array (ALMA) radio telescopes in Chile, mapping the location of cold gas composed of carbon monoxide in the image.
Credit
X-ray: NASA/CXC/Northwestern Univ./M. Gorski; Radio: ESO/NAOJ/NRAO/ALMA; Image processing: NASA/CXC/SAO/K. Arcand and P. Edmonds
X-ray data from NASA’s Chandra X-ray Observatory.
Credit
X-ray: NASA/CXC/Northwestern Univ./M. Gorski; Radio: ESO/NAOJ/NRAO/ALMA; Image processing: NASA/CXC/SAO/K. Arcand and P. Edmonds
Image of the Milky Way center from NASA’s Chandra X-ray Observatory.
Credit
NASA/CXC/UMass/D. Wang et al.
Composite image of the Milky Way center, combining radio date from ALMA and X-ray data from Chandra.
Credit
ALMA(ESO/NAOJ/NRAO)/S. Longmore et al. Background: ESO/D. Minniti et al.
Journal
The Astrophysical Journal Letters
Method of Research
Observational study
Article Title
The discovery of a large active wind from the Milky Way’s central black hole
Article Publication Date
4-Jun-2026
Fastest and most furious ultraviolet wind near a black hole found by York University researchers
York University
image:
An artist's impression of a quasar. The black dot in the center represents the supermassive black hole at the center of the quasar. The red-and-yellow spiral surrounding it shows the disc of hot gas falling into the black hole. Some of this gas is ejected as the quasar's wind, which is shown in light blue. The size of the disc shown is comparable to the size of our Solar System.
view moreCredit: NASA/CXC/M. Weiss, Nahks Tr'Ehnl, Nurten Filiz Ak
TORONTO, June 4, 2026 – A team led by York University researchers has discovered the fastest wind near a supermassive black hole ever found at ultraviolet wavelengths, driven by the disc of matter, or quasar, surrounding the black hole.
“This quasar has a black hole of 1.7 billion times the mass of the Sun. That’s typical. What’s not typical is that it has gas moving towards us at 30 per cent of the speed of light,” says York Professor Patrick Hall of the Faculty of Science.
The finding is published today in a peer-reviewed paper in The Astrophysical Journal, published by The American Astronomical Society.
The research team includes York graduate student and lead author Lucas Seaton, graduate student Marianna Veltri, and undergraduate student Zezhou Zhu, along with colleagues from the University of Washington Bothell and other members of the Sloan Digital Sky Survey (SDSS) collaboration.
“This quasar, known as J2318 (Jay Twenty-Three Eighteen), can be found in the Great Square in the constellation of Pegasus,” says Seaton. “In terms of its speed, this quasar’s wind could be called a category 79 hurricane,” says Seaton. “Every category of hurricane is about 20 per cent faster than the category below it. Calling it category 79 gives an idea of just how fast it is, but of course this wind is unlike anything on Earth.”
Astronomers have known for close to three decades that every large galaxy has a supermassive black hole at its centre, with a mass from millions to billions of times that of the Sun, although contrary to popular belief they do not eat everything in reach. Matter spiraling into one of these black holes forms a disc far bigger than Earth’s orbit around the Sun and hotter than the surface of the Sun. These discs of hot gas, called quasars, generate enough light to be seen across the observable universe and to drive winds from their surfaces.
“In quasars, we often see winds of gas pushed away from the black hole by the light of the quasar,” says Seaton. “The wind in J2318 can be seen at ultraviolet wavelengths at velocities up to 30 per cent the speed of light. Even faster winds can be seen at x-ray wavelengths, but J2318 is the fastest ever discovered at ultraviolet wavelengths.”
Unlike the differences in gas pressure that drive atmospheric winds on Earth, winds from quasars are pushed at least in part by light itself. Individual packets of light (called photons) bounce off or are absorbed by atoms in the gas and accelerate them.
“Quasars put out so many photons that those tiny pushes add up to extreme velocities,” says Seaton. “The problem is, the photons can also remove all the electrons from the atoms, making them invisible. How to push the gas to the speeds we see while keeping the carbon and silicon ions we see intact… it’s quite a puzzle.”
The discovery relied on data from two components of the SDSS, an international survey of the night sky to which hundreds of astronomers have contributed since its start in 1998, specifically, the SDSS-IV Time-Domain Spectroscopic Survey and the SDSS-V Black Hole Mapper. Veltri flagged the quasar as potentially interesting in SDSS-V in 2023 while an undergrad student at York. After looking at it using software set up by Zhu, Hall realized it had an extremely fast wind.
“Canada has a share of the eight-meter-diameter Frederick C. Gillett Gemini Telescope (also known as Gemini North) in Hawai’i, and we immediately proposed observations with it. They succeeded in confirming its record-breaking wind velocity,” he says, adding that he often involves York undergraduates in research as part of his participation in the SDSS.
He explains that “just as a rainbow spreads the Sun’s light into different wavelengths (colours), the SDSS spreads out the light from certain stars, galaxies, and quasars into what we call their ‘spectra’. From those spectra, with practice, students learn to spot unusual quasars. In the past, only PhD astronomers or graduate students studying for a PhD would have made a discovery like this, but the SDSS enables undergraduates to do so.”
Study co-author, Associate Professor Paola Rodríguez Hidalgo of the University of Washington at Bothell, adds: “Both Patrick and I have been working together and with undergraduate students thanks to the SDSS Faculty and Students Team (FAST) initiative that supports these collaborations. Initiatives like this allow students to focus on research while finishing their undergraduate studies. These students will be the next generation of scientists and are already making scientific discoveries.”
Co-author Liliana Flores, who worked with Professor Rodríguez Hidalgo as an undergraduate at UW Bothell and was a FAST participant, says she was thrilled to contribute to the study of this extreme outflow case. “I was in charge of fitting the absorption profiles in the quasar spectrum to determine their velocity and equivalent widths. Repeated observations revealed that the amount of absorbed light changes over time. Something in the wind conditions must be changing for that to happen.”
Veltri assembled measurements of the brightness of the quasar from 20 years of surveys, starting with the original SDSS. That data shows that J2318 is slowly varying in brightness in a way indistinguishable from other quasars. Only by taking detailed measurements of spectra with SDSS was the wind in J2318 revealed.
Rodríguez Hidalgo calls the discovery exciting. “These extreme outflows carry incredible amounts of energy that can affect the galaxies around them. They serve as a sort of missing link: the elusive feedback between the active central region of a galaxy and the rest of the galaxy. While this process has been included in simulations of galaxy formation for decades, a lot more work needs to be done to understand it from observations and make sure the simulations handle it correctly.”
Searches are continuing for more extremely high velocity outflows from quasars, says Flores. “It won’t be easy to find a faster ultraviolet outflow than that of J2318, but we are continuing this search from the nearby universe to the most distant reaches of the universe that we can see.”
Illustration: “Just quasar art” version of the image here: https://www.sdss3.org/press/images/fullsize/wind.justart.300dpi.tiff
Illustration Description: An artist's impression of a quasar. The black dot in the center represents the supermassive black hole at the center of the quasar. The red-and-yellow spiral surrounding it shows the disc of hot gas falling into the black hole. Some of this gas is ejected as the quasar's wind, which is shown in light blue. The size of the disc shown is comparable to the size of our Solar System.
Joint with:
Sloan Digital Sky Survey
University of Washington Bothell
The Pennsylvania State University (local only)
# # #
York University is a modern, multi-campus, urban university located in Toronto, Ontario. Backed by a diverse group of students, faculty, staff, alumni and partners, we bring a uniquely global perspective to help solve societal challenges, drive positive change, and prepare our students for meaningful life and career paths. York's Glendon Campus is home to Southern Ontario's Centre of Excellence for French Language and Bilingual Postsecondary Education. York’s campus in Costa Rica offers students exceptional transnational learning opportunities and innovative programs, while at the Markham Campus, innovation, technology, entrepreneurship and industry collaboration are built into every program. York’s new School of Medicine, the first Canadian medical school to focus on community-based primary health-care education, will welcome its first cohort in September 2028. York was recently named one of Canada’s Greenest Employers for the 14th consecutive year. Together, we can make things right for our communities, our planet, and our future.
Journal
The Astrophysical Journal
Article Title
A New Member of the Fast and Furious Family: A Relativistic and Time-variable UV Outflow in a Luminous Quasar
Article Publication Date
4-Jun-2026
Multiangle simulations uncover how neutrinos can help or hinder supernova explosions
Researchers leverage a multiangle simulations approach to elucidate the roles of neutrino fast flavor conversion affects core-collapse supernova explosions
image:
Researchers elucidate the bifurcated impact of neutrino fast flavor conversion on the core-collapse supernova explosion mechanism.
view moreCredit: Assistant Professor Ryuichiro Akaho from Waseda University, Japan
Our universe, filled with galaxies and stars, is full of mysteries. Over the centuries, astronomers have observed and documented supernova—the catastrophic explosion of stars—as some of the brightest and most energetic events in the universe. In particular, at the end of their lives, massive stars explode into core-collapse supernovae (CCSNe). Scientists believe these explosions to be mainly facilitated by neutrino-mediated energy transport. However, the effects of collective neutrino oscillations known as fast flavor conversion (FFC) on the CCSN explosion mechanism remain largely unclear.
Previous studies attempted to investigate the role of FFC in CCSNe using approximate “truncated moment” methods. However, these approaches cannot reliably capture the angular neutrino distributions needed to determine where FFC occurs.
A new study instead employs a multiangle treatment, allowing the researchers to directly model the angular behavior of neutrinos in momentum space.
The team of researchers, led by Assistant Professor/Junior Researcher Ryuichiro Akaho from the Faculty of Science and Engineering at Waseda University, Japan, along with co-authors Dr. Hiroki Nagakura from the National Astronomical Observatory of Japan and Professor Shoichi Yamada from Waseda University, has carried out CCSN simulations with multiangle neutrino transport to elucidate the impact of neutrino FFC on CCSNe. Their insightful findings were made available online on May 11, 2026, and have been published in Volume 136, Issue 19 of the journal Physical Review Letters on May 15, 2026. The paper was also selected as a “Featured in Physics” article by the journal editors, recognizing its significance and broad interest to the physics community.
In this study, the team combined a quantum kinetic theory-based FFC model with multidimensional Boltzmann neutrino radiation hydrodynamics simulations. Their framework directly identifies where FFC occurs using neutrino angular distributions calculated during the simulation itself. Akaho remarks: “We deploy our first-ever Boltzmann radiation hydrodynamics code that implements an FFC subgrid model, judge the occurrence of FFC directly from angular distributions obtained in simulations, and ascertain neutrino flavor states via physics-based quantum kinetic methods implemented through the Bhatnagar-Gross-Krook relaxation scheme. Crucially, we have already demonstrated this extended framework of neutrino transport in our previous work.”
The CCSN simulations presented in this study encompass successful as well as failed explosions, various progenitor models with zero-age main sequence masses of 9, 12, 16, and 20M⊙, and three different nuclear equations of state (EOSs), namely, variational method-based Furusawa-Togashi EOS, Dirac-Brückner-Hartree-Fock technique, and chiral effective field theory.
The researchers remarkably found that the impact of FFC on CCSN explosion is bifurcated depending on the progenitors. While FFC promotes shock revival and boosts the explosion energy for the lowest-mass progenitor, it has an inhibitory impact for higher-mass progenitors. The mass accretion rate is the main determinant governing this bifurcated effect. For a high value of mass accretion rate, the contribution of FFC to neutrino heating turns out to be negative, since the concurrent reduction in neutrino luminosity dominates over the enhancement of heating efficiency through FFC-driven spectral hardening of electron-type neutrinos. In contrast, FFC contribution to neutrino heating becomes positive for a low mass accretion rate.
“Our present results highlight the limitations of approximate neutrino transport and show that a multiangle treatment is essential for accurately capturing FFC effects. Otherwise, important FFC signals may be overlooked or even falsely identified,” highlights Akaho.
Overall, this work provides a robust argument for the involvement of neutrino FFC in the explosion mechanism of CCSNe, improving our understanding of the lifecycle of massive stars and potentially serving as a theoretical guide for future CCSN observations.
***
Reference
DOI: https://doi.org/10.1103/fksy-1jtw
Authors: Ryuichiro Akaho1, Hiroki Nagakura2, Wakana Iwakami1, Shun Furusawa3, Akira Harada4,5, Hirotada Okawa6, Hideo Matsufuru7, Kohsuke Sumiyoshi8, and Shoichi Yamada1
Affiliations:
1Faculty of Science and Engineering, Waseda University
2Division of Science, National Astronomical Observatory of Japan
3College of Science and Engineering, Kanto Gakuin University
4Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS), RIKEN
5National Institute of Technology, Ibaraki College
6Faculty of Software and Information Technology, Aomori University
7High Energy Accelerator Research Organization
8National Institute of Technology, Numazu College
About Waseda University
Located in the heart of Tokyo, Waseda University is a leading private research university that has long been dedicated to academic excellence, innovative research, and civic engagement at both the local and global levels since 1882. The University has produced many changemakers in its history, including eight prime ministers and many leaders in business, science and technology, literature, sports, and film. Waseda has strong collaborations with overseas research institutions and is committed to advancing cutting-edge research and developing leaders who can contribute to the resolution of complex, global social issues. The University has set a target of achieving a zero-carbon campus by 2032, in line with the Sustainable Development Goals (SDGs) adopted by the United Nations in 2015.
To learn more about Waseda University, visit https://www.waseda.jp/top/en
About Assistant Professor Ryuichiro Akaho from Waseda University
Dr. Ryuichiro Akaho is an Assistant Professor in the Faculty of Science and Engineering at Waseda University, Japan. His research focuses on computational astrophysics, neutrino radiation hydrodynamics, and the explosion mechanisms of core-collapse supernovae. He specializes in multidimensional Boltzmann neutrino transport simulations and studies the role of neutrino flavor conversion in massive stellar explosions. His work aims to advance the theoretical understanding of supernova dynamics and neutrino physics through large-scale numerical simulations.
Journal
Physical Review Letters
Method of Research
Computational simulation/modeling
Subject of Research
Not applicable
Article Title
Bifurcated Impact of Neutrino Fast Flavor Conversion on Core-Collapse Supernovae Informed by Multiangle Neutrino Radiation Hydrodynamics
Gravitational waves in a humming Universe
Gravitational waves are tiny ripples in spacetime. Their first direct detection in 2015 marked a revolutionary moment in astronomy. Today, we have a thorough understanding of signals that travel far from their sources through quiet, nearly empty space, such as those emitted when black holes merge. In this case, the wave can be considered a minor disturbance on a silent background. The distinction between 'background' and 'wave' is clear, and the quantity measured by the detector — a tiny stretching and squeezing — is clearly determined.
In cosmology, however, things are more subtle. The focus shifts to the universe in its entirety — encompassing spacetime and everything contained within it, such as stars, black holes and galaxies. The background itself is dynamic. Small fluctuations in density and velocity gently stir spacetime everywhere, blurring the boundary with the wave. But what exactly does a gravitational-wave detector measure when the entire universe is gently vibrating? Previously, theoretical predictions were entirely dependent on the choice of mathematical coordinates. However, the only meaningful quantity is what a real instrument records, which must be coordinate-independent.
Dr. Guillem Domènech and his team at the Institute of Theoretical Physics of Leibniz University Hannover (LUH) have now developed a precise detector-based approach. Instead of discussing the components of an abstract field, the researchers model a realistic experiment involving two freely falling test masses, or atomic clocks, linked by a light beam. A passing gravitational wave can slightly alter the travel time of light, thereby affecting the measured time or frequency signal. The authors derive this observable in full and in a coordinate-independent manner, up to second order in cosmic fluctuations.
“Gravitational wave detectors measure differences in the frequencies and arrival times of light beams,” says lead author Guillem Domènech. “We calculate these quantities exactly within an expanding spacetime and distinctly isolate what is genuinely measurable from effects that rely on the mathematical description. This ensures that theoretical predictions for future experiments are rigorous and reliable.”
This approach establishes a shared vocabulary for theory and experimentation. In the 'quiet spacetime' limit, it reduces to the familiar measurement taken using ground-based interferometers. In a cosmological setting, however, it remains unambiguous and robust. This provides a reliable theoretical framework to guide the search for primordial gravitational waves in the universe— with direct relevance for current and future measurements, such as those using pulsar timing arrays and the space-based observatory LISA.
Original publication:
Observable Gravitational Wave Strain at Second Order
Guillem Domènech and Shi Pi and Ao Wang
Phys. Rev. Lett.
DOI: https://doi.org/10.1103/pwbs-xwrh
Note to editors:
For further information, please contact Dr. Guillem Domènech, Institute of Theoretical Physics at Leibniz University Hannover (tel. 0511 762-3886, email: guillem.domenech@itp.uni-hannover.de).
