Researchers have found evidence of stellar explosions so powerful they leave nothing behind

A supernova – the explosive death of a star – is always violent, throwing matter into space and usually leaving behind a compact stellar remnant, such as a neutron star or black hole. But some supernovae involving the largest stars in the cosmos can be so extremely powerful that they leave absolutely nothing behind, Reuters reports.

Scientists have theorized the existence of these ultra-powerful supernovae since the 1960s, and now they've found evidence for them, albeit indirectly, in research involving black holes and ripples in spacetime called gravitational waves.

Hui Tong, a doctoral student in astrophysics at Australia's Monash University and lead author of the study published Wednesday in the journal Nature, said such supernovae occur at the end of the life cycle of the most massive stars — those with a mass of about 140 to 260 times that of the Sun.

“Despite their huge mass, they have relatively short lives, on the order of a few million years. By comparison, the Sun will live for about 10 billion years, so these stars use up their fuel about a thousand times faster – like a massive firework that burns intensely and briefly before exploding,” the researcher told Reuters.

The research team studied more than 150 black holes

The explosion of large stars of a certain mass leaves behind a neutron star – a collapsed and compact stellar core. When some even larger stars explode, they leave behind a black hole, an extremely dense object with a gravity so strong that not even light can escape. The black hole retains some of the original mass of the star, the rest being thrown into space.

For the new study, the researchers analyzed data from 153 pairs of black holes, calculating their mass based on the gravitational waves they emit, and then separated black holes that had previously formed by merging two smaller black holes.

What they later detected was the absence of black holes with masses between about 44 and 116 solar masses, a range they called the “forbidden range”.

The researchers say this absence can best be explained if the most massive stars, which we would expect to leave behind black holes in this mass range, were actually annihilated at the end of their lives in a rare type of explosion called a “pair instability supernova,” leaving no trace.

“A pair instability supernova is one of the most violently explosive types of stellar death,” explained Maya Fishbach, an astrophysicist at the University of Toronto's Canadian Institute for Theoretical Astrophysics and co-author of the study.

Massive stars rapidly reaching the end of their lives

In general, massive stars form black holes. The more massive the star, the heavier the black hole, until stars reach a certain mass threshold beyond which the physics of their explosive disintegration dictates that no stellar remnant remains.

These giant stars initially evolve in a similar way to other massive stars, burning hydrogen and helium and accreting a large core composed mainly of carbon and oxygen.

For the core to remain stable, there must be a balance between the inward gravitational pressure and the outward release of energy—in the form of high-energy photons (the particles that make up light), in the case of these stars.

But at the extreme temperatures inside these stars, some of the photons turn into pairs of subatomic particles called electrons and positrons, thus weakening the outward pressure that contributed to maintaining the stability of the nucleus. These pairs of particles and the instability they cause give this class of supernovae its strange name.

“The core becomes unstable, leading to an accelerated collapse, followed by a violent thermonuclear explosion that tears the star apart,” Tong said.

Evidence after six decades of theory

Although these supernovae were first predicted six decades ago, Fishbach said “they are rare and difficult to find and identify.”

The evidence presented in this study may represent the clearest indication yet of the existence of pair-instability supernovae.

“Basically, we're using something invisible, black holes, as an archive of some of the brightest explosions in the universe,” Tong said.