Astronomers Find Hints of Star Population That Failed to Explode
LIGO–Virgo–KAGRA observations find evidence for black holes that may have formed after quietly imploding
When the most massive stars in the universe die, they often detonate in fiery supernovae, dramatically blasting most of their matter into space. The remaining stellar cores collapse into neutron stars and, sometimes, black holes. However, theories suggest that some massive stars might die without a bang, instead directly collapsing inward to become neutron stars or black holes.
Now, a new Caltech-led study using data from the LIGO–Virgo–KAGRA network of gravitational-wave observatories finds hints of a distinct population of black holes that may have formed from such failed supernovae. While the study did not find direct evidence for failed supernovae, it does show that previous gravitational-wave observations match what theorists had predicted for such a population.
LIGO, the National Science Foundation (NSF)-funded Laser Interferometer Gravitational-wave Observatory, which consists of detectors in Louisiana and Washington, made history in 2015 with the first direct detection of gravitational waves, or ripples in space-time, from a pair of colliding black holes. Since then, the Virgo detector in Italy and the Kamioka Gravitational-wave Detector (KAGRA) in Japan, have joined together in one network that has spotted more than 300 black hole collisions.
"A vast majority of the merging black holes in the universe are about 10 times the mass of our Sun," says LIGO team member Katerina Chatziioannou, a professor of physics at Caltech and a William H. Hurt Scholar. "Our data are showing that this group of black holes may have a common origin—they may be a distinct subpopulation that failed to go supernova. These results represent a connection between the gravitational-wave data and underlying astrophysics we are trying to extract."
Chatziioannou led the new research, which has been published in the journal Physical Review D. The lead author is Isaac Legred (PhD '25), a postdoc at the University of Illinois Urbana-Champaign who performed the research while at Caltech. Former Chatziioannou lab member Jacob Golomb (PhD '25), now at Asari AI, is also an author.
To date, no concrete examples of failed supernovae have been confirmed, though the idea is well supported theoretically. Theorists had proposed that a large population of merging black holes, each with masses around ten times the mass of our Sun, may represent some of these failed supernovae. That means that either the most massive black hole of the pair, or both of them, may have originated when a star imploded rather than exploded. The goal of the Caltech-led team was to see if this idea was consistent with the gravitational-wave data.
In the study, the researchers looked at the distribution of the masses of 257 black hole mergers detected by the LIGO–Virgo–KAGRA network over the past 10 years. The data revealed a dramatic peak of black holes at 10 solar masses—three-quarters of the entire sample of mergers. And for the first time, the team found a distinct lack of black holes in the 12 to 16 solar-mass range.
"We see 10 solar-mass black holes merging all the time," Legred says. "But why are, say, 14 solar-mass black holes so rare? The gap we see in the distribution of masses indicates there may be a special cocktail of internal physics that goes into forming the abundance of 10 solar-mass black holes."
The scientists also looked at the distribution of the rates at which those black holes spin (the spins are also influenced by how the black holes formed). This revealed that the population of 10 solar-mass black holes fell into a narrower range of spin rates than the overall sample of black holes. Together, the findings support the idea that the 10 solar-mass black holes are distinct from the overall population, and thus likely have a common origin—possibly the result of the quiet implosion of massive stars.
"We can look up at the sky and try to study historical records of massive stars that failed to explode, but it's challenging because they just vanish without exploding, leaving a dark patch of sky," Legred says. "With this study, we show the gravitational-wave data are consistent with most binary black holes forming from a very special kind of failed supernova, but more research is needed. Black holes are born in some of the most extreme environments in the universe, so the prospect of better understanding their formation is very exciting."
The study titled "Low-mass failed supernovae and the 10 peak in the merging black hole mass distribution," was funded by the National Science Foundation, the U.S. Department of Energy, and the Simons Foundation. LIGO is operated by Caltech and MIT.
Katerina Chatziioannou
Isaac Legred
These pictures taken by NASA's Hubble Space Telescope in 2007 and 2015 show an example of a star thought to have died via a failed supernova. A giant star N6946-BH1 is seen before and after it vanished out of sight, likely after imploding to form a black hole.
Credit: NASA/ESA/C. Kochanek (OSU)
