Researchers have uncovered indirect evidence supporting a theory that has captivated astronomers for over 60 years – the existence of stellar explosions so powerful they completely annihilate the largest stars in the universe, leaving no trace behind.
When massive stars die in supernova explosions, they typically leave behind either neutron stars or black holes. However, scientists have long theorized that the most enormous stars undergo a different fate entirely – complete obliteration through ultra-violent explosions called pair-instability supernovas.
A new study published Wednesday in the journal Nature provides compelling evidence for these theoretical explosions by analyzing gravitational wave data from 153 pairs of black holes. The research team, led by Hui Tong, a doctoral student in astrophysics at Monash University in Australia, discovered a notable absence of black holes weighing between 44 and 116 times the mass of our sun.
The missing black holes in this “forbidden range” suggest that stars massive enough to create such remnants are instead completely destroyed by pair-instability supernovas, according to the researchers.
These catastrophic explosions occur in stars weighing approximately 140 to 260 times more than our sun. Despite their enormous size, these stellar giants have remarkably short lifespans.
“Despite their enormous mass, they live relatively short lives, about a few million years. For comparison, the sun will live for about 10 billion years, so these stars burn out roughly a thousand times faster – like a massive firework that burns intensely and briefly before exploding,” Tong explained.
The explosive mechanism behind these events involves extreme physics occurring within the star’s core. As these massive stars burn hydrogen and helium, they develop cores primarily composed of carbon and oxygen. The core’s stability depends on balancing gravitational pressure with outward energy from high-energy photons.
However, at the extreme temperatures inside these stars, some photons transform into electron-positron particle pairs, weakening the outward pressure that maintains core stability.
“The core becomes unstable, leading to a runaway collapse and then a violent thermonuclear explosion that blows the star apart,” Tong said.
Maya Fishbach, an astrophysicist at the University of Toronto’s Canadian Institute for Theoretical Astrophysics and study co-author, emphasized the extreme nature of these events.
“A pair-instability supernova is one of the most violently explosive types of stellar deaths,” Fishbach noted.
She explained that while massive stars typically form black holes, with heavier stars creating more massive black holes, there’s a critical threshold where the physics changes completely.
“For the most part, massive stars make black holes. The more massive the star, the heavier the black hole,” Fishbach said, until stars reach a certain mass threshold beyond which the physics of their explosive demise dictates that there is no stellar remnant left behind.
Although astronomers have observed superluminous supernovas – explosions more than 10 billion times brighter than our sun – that could potentially be pair-instability events, confirming their true nature remains challenging.
“They are rare and difficult to find and identify,” Fishbach noted about these theoretical explosions first predicted in the 1960s.
The current research may provide the strongest evidence yet for these cosmic phenomena by using an innovative approach.
“We are essentially using something invisible, black holes, as a record of some of the brightest explosions in the universe,” Tong explained.
