Astronomers discover direct link between supernovae and the formation of black holes or neutron stars

Astronomers have discovered a direct link between the explosive deaths of massive stars and the formation of the most compact and enigmatic objects in the universe: black holes and neutron stars. With the help of ESO’s Very Large Telescope (VLT) and ESO’s New Technology Telescope (NTT), two teams were able to observe the aftermath of a supernova explosion in a nearby galaxy, finding evidence of mysterious compact object that she left behind.

When massive stars reach the end of their lives, they collapse so quickly under their own gravity that a violent explosion known as a supernova ensues. Astronomers believe that after all the excitement of the explosion, what remains is the ultra-dense core, or compact remains, of the star. Depending on the mass of the star, the compact remnant will either be a neutron star – an object so dense that a teaspoon of its material would weigh about a trillion kilograms here on Earth – or a black hole – an object of which nothing , not even light can escape.

Astronomers have found many clues hinting at this chain of events in the past, such as the discovery of a neutron star in the Crab Nebula, the cloud of gas left behind by the explosion of a star years ago almost a thousand years. But they had never seen this process happening in real time, meaning that direct evidence of a supernova leaving behind a compact remnant has remained elusive.

“In our work, we make a direct connection,” says Ping Chen, a researcher at the Weizmann Institute of Science in Israel and lead author of a study published Jan. 10 in Nature and presented at the 243rd meeting of the American Astronomical Society in New Orleans, USA

The researchers’ stroke of luck came in May 2022, when South African amateur astronomer Berto Monard discovered the supernova SN 2022jli in the spiral arm of the neighboring galaxy NGC 157, located 75 million light years away. . Two separate teams focused their attention on the aftermath of this explosion and discovered that it had unique behavior.

After the explosion, the brightness of most supernovae simply fades over time; astronomers note a gentle and progressive decline in the “light curve” of the explosion. But the behavior of SN 2022jli is very peculiar: as the overall brightness decreases, it does not do so smoothly, but oscillates up and down approximately every 12 days.

“In the SN 2022jli data, we see a repeating sequence of brightening and fading,” says Thomas Moore, a doctoral student at Queen’s University in Belfast, Northern Ireland, who led a study of the supernova published in the end of last year in The Astrophysics Journal. “This is the first time that repeated periodic oscillations, over several cycles, have been detected in a supernova light curve,” Moore noted in his paper.

Moore and Chen’s teams think that the presence of more than one star in the SN 2022jli system could explain this behavior. In fact, it’s not uncommon for massive stars to orbit a companion star in what’s called a binary system, and the star behind SN 2022jli is no exception. What is remarkable about this system, however, is that the companion star appears to have survived the violent death of its partner and that both objects, the compact remnant and the companion, probably continued to spin the one around the other.

The data collected by the Moore team, which included observations with ESO’s NTT in Chile’s Atacama Desert, did not allow them to determine exactly how the interaction between the two objects caused the ups and downs. bottom of the light curve. But the Chen team had additional observations. They saw the same regular fluctuations in the system’s visible brightness as those detected by the Moore team, and they also spotted periodic movements of hydrogen gas and bursts of gamma rays in the system. Their observations were made possible thanks to a fleet of instruments on the ground and in space, including the ESO VLT X-shooter, also located in Chile.

Putting all the clues together, the two teams generally agree that when the companion star interacted with material released during the supernova explosion, its hydrogen-rich atmosphere became more inflated than usual . Then, as the compact object left behind after the explosion passed through the companion’s atmosphere in its orbit, it stole hydrogen gas, forming a hot disk of material around it. This periodic flight of matter, or accretion, released a lot of energy that was captured as regular changes in brightness in the observations.

Although the teams were unable to observe light coming from the compact object itself, they concluded that this energy theft could only be due to an invisible neutron star, or possibly a black hole , attracting matter from the companion star’s inflated atmosphere. “Our research is like solving a puzzle by gathering all possible evidence,” Chen says. “All these pieces lining up lead to the truth.”

With the presence of a black hole or neutron star confirmed, there is still much to discover about this enigmatic system, including the exact nature of the compact object or the end that could await this binary system. Next-generation telescopes, such as ESO’s Extremely Large Telescope, scheduled to come online later this decade, will help, allowing astronomers to reveal unprecedented details of this unique system.