Cosmic Mystery Solved: Scientists Find Why Some Exploding Stars Don't Become Black Holes

Hyderabad: An international team of scientists, led by Australia's Monash University, has uncovered evidence of a rare form of exploding star, helping shed light on one of the most cataclysmic events in the universe.

At the end of their lifespans, most massive stars collapse into black holes—objects with gravitational pull so strong that even light cannot escape. However, some stars that are extremely massive are thought to reach such high temperatures that they explode in what is called a pair‑instability supernova. This type of explosion is so powerful that the star is completely destroyed, leaving no black hole behind.

First proposed in the 1960s, pair‑instability supernovae remain difficult to distinguish from the more common stellar explosions that do result in black holes.

The new research discovered that by using gravitational waves—ripples in the fabric of spacetime detected by the LIGO-Virgo-KAGRA observatory network—the properties of black holes can be measured. This allowed them to find a "forbidden mass range" where stars seemingly don’t make black holes.

The study says that black holes with masses more than 45 times the mass of our Sun are rare because the stars that might otherwise have made them exploded in pair-instability supernovae. The findings have been published in the journal Nature.

“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,” said project lead, 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).

Researchers believe that by confirming the existence of this gap, they can find out the origin of black holes and help answer a major question about how the most massive stars live and die.

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.

“It’s a cool result because we are using black holes to learn about the nuclear reactions inside stars,” said Professor Eric Thrane, Chief Investigator at OzGra.