August 25, 2026

Are all merging compact objects that produce gravitational waves black holes, or are some of them highly convincing imposters?

A new study published on August 14, 2026 in the prestigious journal Physical Review Letters has brought scientists one step closer to answering this fundamental question. Co-led by Dr. Aditya Vijaykumar, a Postdoctoral Fellow at the Canadian Institute for Theoretical Astrophysics (CITA) at the University of Toronto, the research uses recent gravitational wave data to check for “Exotic Compact Objects” (ECOs)—hypothetical structures that mimic black holes but lack an event horizon from which nothing can escape.

The international research team focused their attention on GW241011, a massive gravitational wave event generated by a violent cosmic collision. The larger of the two colliding bodies (the “primary”) was roughly 20 times the mass of our sun and spinning incredibly fast, making it the perfect laboratory to test the laws of fundamental physics.

To determine if this object was a true black hole or an exotic imposter, the team measured its “spin-induced quadrupole moment.”

“When an object spins rapidly, it bulges at its equator. How much it bulges depends entirely on what it is made of,” explains Dr. Vijaykumar, one of the lead authors of the study. “Because the more massive object in GW241011 was spinning so fast, the gravitational wave data provided us with the tightest constraints ever recorded on this bulging effect. This allowed us to test beyond the standard realm of black holes.”

One of the leading theoretical candidates for black hole imposters is a “Boson star”—a hypothetical compact object that��would be made of a yet-to-be-discovered heavy Boson particle (like the theoretical “Axion”). Because Bosons��can��share the exact same space, they don’t push back the way neutrons do. They just peacefully overlap into a giant, dense, quantum fluid blob. The theoretical models of Boson stars anticipate that their��shape would be distorted by rotation in a way that differs from that of a spinning black hole.

By analyzing the data from GW241011, Vijaykumar and his colleagues presented compelling evidence that the primary object in the spinning binary was not distorted enough to fit the hypothetical model of a rotating Boson star – specifically, not the kind characterized by quartic self-interactions, effectively ruling out this exotic model for this event.

However, the mystery of Exotic Compact Objects is far from solved. The study notes that while certain Boson stars have been eliminated, other highly dense theoretical models—specifically those with an extreme “compactness” factor greater than 0.24 (black holes have compactness value of 0.5)—are still viable contenders for what this object might have been.

“This is a thrilling era for astrophysics,” says Vijaykumar. “With the increasing sensitivity of gravitational wave detectors like LIGO, Virgo, and KAGRA, we are no longer just guessing about what exists in the deep universe. We are actively stress-testing the standard model of particle physics and general relativity in real-time.”

The paper, led by Dr. Vijaykumar along with Dr. Tamara Evstafyeva (Perimeter Institute) and Dr. NV Krishnendu (University of Birmingham), places some of the most stringent constraints on beyond-Kerr black hole physics to date and establishes a vital new framework for how scientists will analyze future gravitational wave detections.

To read the full study��go to:. Phys. Rev. Lett. 137, 071402.

������Ƶ the Canadian Institute for Theoretical Astrophysics (CITA)
Located at the University of Toronto, CITA is a globally recognized research institute dedicated to advancing our understanding of the universe. CITA researchers specialize in theoretical astrophysics, cosmology, and fundamental physics, driving innovation in our understanding of black holes, dark matter, and gravitational waves.

SCIENCE CONTACT:��Dr. Aditya Vijaykumar

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

April 16, 2026

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’.

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!”

Nature��paper, “Evidence of the pair-instability gap from black-hole masses”,��

Read more:��,����and .

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