Supernovae give rise to black holes or neutron stars

Using the European Southern Observatory's Very Large Telescope (VLT) and the New Technology Telescope (NTT), a team of astronomers has made a groundbreaking discovery - revealing a direct connection between supernovae, the explosive deaths of massive stars, and the formation of the universe's most enigmatic objects - black holes and neutron stars.

The two teams observed the aftermath of a supernova explosion in a nearby galaxy, finding evidence for the mysterious compact object it left behind.

When massive stars reach the end of their lives, they undergo a catastrophic explosion called supernova and leave behind the ultra-dense core, or compact remnant. The compact remnant left by the dying star will be either a neutron star or a black hole, depending on the star's mass. Neutron stars are incredibly dense, with a teaspoon of their material weighing around a trillion kilograms on Earth. Black holes, on the other hand, are objects from which nothing, not even light, can escape.

"Our research is like solving a puzzle by gathering all possible evidence," said Ping Chen, a researcher at the Weizmann Institute of Science, Israel, and lead author of a study published today in Nature.

In May 2022, South African astronomer Berto Monard discovered the supernova SN 2022jli in the spiral arm of NGC 157, a galaxy located 75 million light-years away from Earth. Two different teams investigated the aftermath of the explosion and discovered its unique behavior.

Following the explosion, majority of supernovae gradually lose their brightness over time, exhibiting a smooth decline in the explosion’s 'light curve'. However, in the case of SN 2022jli, the overall brightness declines, oscillating up and down approximately every 12 days or so.

"This is the first time that repeated periodic oscillations, over many cycles, have been detected in a supernova light curve," noted Thomas Moore, a doctoral student at Queen’s University Belfast, Northern Ireland, who led a study of the supernova published late last year in the Astrophysical Journal.

Both teams proposed that the peculiar behavior of SN 2022jli could be explained by the presence of more than one star in the system. It is quite common for massive stars to be in orbit with a companion star in a binary system, and the star that caused SN 2022jli was no exception, the researchers said. 

However, what makes this system extraordinary is that the companion star seems to have survived the catastrophic demise of its partner. The compact remnant and the companion star are likely kept orbiting each other.

Although the Moore team didn't discover the exact cause of the variations in the light curve due to the interaction between the two objects, the Chen team identified similar regular fluctuations in the system's visible brightness as the Moore team had observed. The latter also observed periodic movements of hydrogen gas and bursts of gamma rays in the system.

Both teams agreed that during the supernova explosion, when the companion star interacted with the ejecta, its hydrogen-rich atmosphere became puffier than usual. As the compact object from the supernova passed through the atmosphere of the companion on its orbit, it would take hydrogen gas from it, forming a hot disc of matter around itself. The accretion would release a significant amount of energy, which caused regular changes in brightness that were observed.

The teams were unable to observe any light emanating from the compact object. However, they concluded that the energy theft was caused by an unseen neutron star or a black hole, attracting matter from the atmosphere of its companion star with a puffy atmosphere.

Using ESO's #VLT and NTT, among other instruments, astronomers have found direct evidence that #supernovae 💥 give rise to #BlackHoles or neutron stars — a process at which prior clues hinted, but which had never been witnessed in real time until now. 1/ pic.twitter.com/WMSzWuD5BC

— ESO (@ESO) January 10, 2024