Publications – Canadian Institute for Theoretical Astrophysics

Supercomputer Reveals How Exploding Stars “Stir” the Galaxy from the Bottom Up

citaadmin — Mon, 01 Jun 2026 21:28:45 +0000

Supercomputer Reveals How Exploding Stars "Stir" the Galaxy from the Bottom Up

June 1, 2026

Caption (works for any): the explosions of dead stars extracted from a simulation of a galactic disk. The most intense colors indicate where the turbulence in the explosions is being generated from, which traces an unstable thin shell around the dead stars.

New research performed on the at the University of Toronto reveals a fundamentally different mechanism by which exploding stars shape the turbulent structure of our galaxy. The study, authored by , postdoctoral fellow at the Canadian Institute for Theoretical Astrophysics (CITA), was accepted for publication in . It challenges long-standing assumptions about how turbulence is generated and sustained in the interstellar medium.

Turbulence—the chaotic, swirling motion of gas—is a fundamental process in astrophysics, influencing everything from star formation to the transport of energy and magnetic fields across galaxies. For decades, scientists have largely assumed that turbulence in the Milky Way follows a classical cascade: energy injected at large scales breaks down into progressively smaller eddies (vortices or “swirls”), consistent with the well-known Kolmogorov picture.

However, this new work demonstrates that supernova remnants—the expanding shells of gas left behind by stellar explosions—can instead inject turbulence at small scales that, then, propagates upward to larger scales through an inverse cascade. This finding suggests that the dominant source of galactic turbulence may not operate in the way previously thought. Instead of a top-down energy transference (dying out of energy), it’s a bottom-up build-up. His research shows that supernova explosions create microscopic, chaotic swirls first. Those tiny swirls then merge and push their energy upward, eventually creating the massive, large-scale turbulence that shapes our entire galaxy.

“Our results show that the structure of turbulence in the galaxy carries a direct imprint of the physical instabilities that occur in supernova remnants,” said Dr. Beattie. “Rather than simply decaying or cascading downward, turbulence generated at the interfaces within these remnants can grow and reorganize, ultimately influencing dynamics on galactic scales.”

The research identifies the contact discontinuity—the unstable boundary between hot, shocked ejecta and cooler surrounding gas—as a key site of turbulence generation. Instabilities and strong baroclinic effects at this interface drive the formation of vortical motions that seed turbulence at relatively small spatial scales. From there, nonlinear interactions transfer energy to larger scales, producing a turbulent spectrum that deviates significantly from classical expectations.

Crucially, these results were made possible by cutting-edge numerical simulations performed on the Trillium Supercomputer, one of Canada’s most advanced high-performance computing systems operated by SciNet at the University of Toronto. The scale and fidelity required to resolve both the small-scale instabilities and their large-scale consequences demand computational resources at the forefront of modern supercomputing.

This revised picture has broad implications. It provides a new framework for interpreting observations of interstellar turbulence, including velocity fluctuations and magnetic field structure, and may help explain why measured spectra in the Milky Way often differ from theoretical predictions. It also suggests that models of galaxy evolution and star formation may need to be re-evaluated to account for this alternative turbulent driving mechanism.

Beyond its implications for the Milky Way, the work points to a more general principle: that microscopic plasma processes and instabilities can leave lasting imprints on macroscopic astrophysical systems.

“This is a shift in perspective,” Dr. Beattie added. “If turbulence in galaxies is seeded at small scales by physical instabilities, then understanding those instabilities becomes essential for understanding the large-scale universe.”

The paper is available on arXiv:

Beattie, J. 2026,��American Astronomical Society,��,��,��,��Supernovae Drive Large-scale, Incompressible Turbulence through Small-scale Instabilities.

SCIENCE CONTACT: Dr. James Beattie

Media Contact:
Lyuba Encheva, Communications and Events Coordinator
Canadian Institute for Theoretical Astrophysics, University of Toronto
Email: communication@cita.utoronto.ca

New Study Finds Evidence of Cosmic Explosions with Missing Black Holes

citaadmin — Wed, 01 Apr 2026 16:00:47 +0000

New Study Finds Evidence of Cosmic Explosions with Missing Black Holes

April 1, 2026

CITA researchers Maya Fishbach, Amanda Farah and Aditya Vijaykumar are part of an international team that has uncovered evidence of a rare form of exploding star, shedding light on one of the most cataclysmic events in the Universe. Their study, published in Nature today, confirms that black holes with masses larger than 45 times the mass of the sun are the result of previous black hole mergers, rather than the collapse of enormous dying stars.

Using data from the LIGO-Virgo-KAGRA observatory network, the international team led by Hui Tong, a PhD candidate from Monash University’s School of Physics and Astronomy and the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav), was able to measure the properties of black holes in the “forbidden range” (of over 45 times the mass of the sun) and confirm the theoretical prediction of ‘pair-instability supernovae’.

This artist’s impression shows a stellar explosion with subtle hints of a black hole binary in the background, released on April 1, 2026. Credit: Carl Knox, OzGrav–Swinburne University of Technology

Why are black holes heavier than 45 solar masses so rare? At the end of their lives, most massive stars collapse into black holes – objects with gravity so strong that not even light can escape. Presumably, the universe’s most massive stars should collapse to form the most massive black holes. However, some very massive stars become so hot that they are blown apart in a pair-instability supernova – an explosion so intense that it destroys the star, leaving no core behind that can collapse into a black hole.

Project lead, Hui Tong, explained that the team’s analysis of gravitational wave signals – the ripples in the fabric of spacetime – detected by the LIGO-Virgo-KAGRA observatory afforded evidence of the existence of the forbidden mass range where stars seemingly don’t make black holes.

“The observation is well explained by pair instability; there are no stellar-origin black holes in the forbidden zone because stars are undergoing pair-instability supernovae. The only black holes in this mass range are made from merging smaller black holes, rather than directly from stars,” Mr. Tong said.

Confirming the existence of this gap would help settle a major question about how the most massive stars live and die, and the origin of black holes.

Project collaborator, Professor Maya Fishbach from the University of Toronto and CITA said the study highlights the potential of gravitational waves to probe the lives, deaths and afterlives of the most massive stars in our Universe.

“We are seeing indirect evidence of one of the most titanic blasts in the cosmos: pair-instability supernovae. At the same time, we are finding that once they are born, black holes can grow via repeated mergers,” said Professor Maya Fishbach.

First predicted in the 1960s, pair-instability supernovae are challenging to distinguish from more common stellar explosions that leave behind black holes. Coauthor Amanda Farah, who is a CITA postdoctoral fellow, commented: “We rarely (if ever) get to see these types of explosions in real-time, so it’s amazing that we can observe their lasting imprints so clearly in the gravitational-wave data. These imprints — the black holes that pair-instability supernovae fail to leave behind — are already teaching us about nuclear physics. This was one of the early promises of gravitational-wave astronomy, and it’s so exciting to see that promise fulfilled today.”

Another CITA postdoctoral fellow, coauthor Aditya Vijaykumar, expects that these new findings are an important step forward in gravitational wave research: “The impact of this work is already being felt across the community. It has already sparked a wave of follow-up research, and there are now multiple lines of evidence suggesting that some black hole mergers involve components born in earlier collisions. Such black hole mergers are thought to be produced in regions of the Universe that host a dense crowd of stars, and I am excited for all that we will learn about these environments in the future. It is a fascinating time for our field!”

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Astronomers pave the way in the search for supermassive black hole binaries in the hearts of galaxies

Mon, 30 Mar 2026 15:48:12 +0000

Astronomers pave the way in the search for supermassive black hole binaries in the hearts of galaxies

March 30, 2026

A team of astronomers including CITA postdoctoral fellow Aretaios Lalakos and CITA Professor Richard Bond,�� has bolstered the evidence for the existence of one of the most remarkable, yet elusive, phenomena in the universe: pairs of supermassive black holes (SMBH) in orbit around each other in the centres of galaxies.

Their research, recently published in the journal Astronomy & Astrophysics, describes the discovery — as well as the “fingerprint” they used to identify the SMBH pairs and how it paves the way for finding more.

Read the rest of the story on .

A visualization depicting two supermassive black holes in orbit around each other.
Photo credit: NASA’s Goddard Space Flight Center/Scott Noble; simulation data, d’Ascoli et al. 2018.

CITA Researcher Helps Locate the “Missing Link” in Giant Black Hole’s Power Source

citaadmin — Wed, 28 Jan 2026 13:00:14 +0000

CITA Researcher Helps Locate the “Missing Link” in Giant Black Hole’s Power Source

January 28, 2026

New data from the Event Horizon Telescope (EHT) has provided scientists with a first-of-its-kind look at the “exhaust pipe” of a supermassive black hole.

James Webb Space Telescope (JWST) + NIRCam RBG image of the giant elliptical galaxy M87. The stream of the glowing torch represents the jet. The visible part spans around 3000 light-years. Credits: Jan Röder, Maciek Wielgus, Joseph B. Jensen, Gagandeep S. Anand, R. Brent Tully, 2025.

, a postdoctoral researcher at the Canadian Institute for Theoretical Astrophysics (CITA), is part of an international team that has identified the likely starting point of a massive cosmic jet — a powerful stream of particles being blasted out from the heart of the galaxy Messier 87 (M87).

The discovery, published today in the journal Astronomy & Astrophysics, contributes to the uncovering of a major mystery in space science: exactly where black holes launch these 5,000-light-year-long streams of energy into the universe.

Finding the Engine Room

At the center of the M87 galaxy lies a black hole with a mass six billion times that of our Sun. While black holes are famous for pulling matter in, they also act as massive engines that eject streams of charged particles—known as “jets”—at nearly the speed of light.

“By identifying where the jet originates and how it connects to the black hole’s shadow, we are adding key pieces to the puzzle,” says Saurabh, the study’s lead author from the Max Planck Institute for Radio Astronomy.

The “Middle View” Discovery

To see this, the team used the Event Horizon Telescope, a global network of radio dishes that work together to create a single virtual telescope the size of the Earth. In the past, the radio observations have provided two different views of M87:

The pre-2021 EHT observations provided the Extreme Close-Up: A “zoomed-in” view showing the famous glowing ring of hot gas around the black hole’s shadow.
Lower frequency radio observations provided the Wide Angle: A “zoomed-out” view showing the long, thin jet stretching across the galaxy.

The “missing link” has always been the area in between—the transition where the glowing ring becomes the jet. By analyzing new data from 2021, von Fellenberg and his colleagues utilized “intermediate” telescope distances to see this middle ground for the first time.

They discovered that the glowing ring alone couldn’t explain all the light they were seeing. Through detailed computer modeling, they found that the “missing light” matches a specific spot about 0.09 light-years away from the black hole. This, they believe, is the place of origin of the black hole’s jet.

A New Era of Black Hole Imaging

The contribution from CITA and the international team marks a shift from simply theorizing about black holes to observing their direct environment. To capture this elusive region, the team relied on a technique called “calibration”—a complex process of cleaning up raw data from the Earth-sized virtual telescope. Sebastiano von Fellenberg of CITA led the calibration for the 2021 M87* observations. By precisely correcting for atmospheric interference and slight hardware differences between telescopes scattered across the globe, he essentially “cleared the static,” allowing the team to see the faint signals of the jet’s origin that were previously hidden.

“Newly observed data—now being processed with support from our international partners—will soon include even more telescopes and thus intermediate baselines,” says Sebastiano von Fellenberg of CITA. “This will bring an even sharper view of the jet launching region within reach. We aren’t just calculating where these structures are anymore; we are moving toward being able to image them directly.”

Observations from 2018 (left), conducted with the Global mm-VLBI Array (GMVA) at frequencies of 86 GHz, show not only the ring around the supermassive black hole M87*, but also a jet that splits into a northern and southern component. At higher frequencies of 230 GHz (right), the EHT data show fine details of the ring, but cannot yet image the jet. A compact region that coincides with the southern part of the jet at 86 GHz best explains the missing radiation at 230 GHz observed at different spatial scales. Figure credit: (Lu. et al. 2023 + Saurabh et al. 2026)

Professor Bart Ripperda, who leads a research group at CITA that studies the causes for the ejection of these powerful streams of charged particles, also explains:

“The jets are theorized to be launched tapping the rotational energy of the black hole through electromagnetism, such that they are a laboratory where general relativity and quantum electrodynamics (the two most successful theories of the 20th century) act together. Seeing how jets are launched so close to the event horizon of the black hole is a major step in the understanding of black holes!”

Observational data, such as the one presented in , allows scientists to test their theories on how gravity and magnetism interact in the most extreme environments in the universe, bringing us one step closer to understanding the “engines” that shape entire galaxies.

Original publication: Saurabh et al. Probing jet base emission of M87* with the 2021 Event Horizon Telescope observations, Astronomy & Astrophysics 705 (2026), DOI: