Black holes and neutron stars are the densest known celestial objects in the universe. So far, we have a lot of clues about the formation of supernovae into black holes or neutron stars, but unfortunately there is no direct observational evidence. It was not until recently that astronomers analyzed the supernova SN 2022jli event and obtained for the first time direct evidence that massive stars undergo supernova explosions and form black holes and neutron stars.
When a massive star reaches the end of its life, it will rapidly collapse under its own gravity, triggering a violent explosion called a supernova. Astronomers believe that after a massive star undergoes this explosion, it will leave behind an ultra-dense core or a compact remnant. Depending on the mass of the star, the remnant may be a neutron star or a black hole.
Advertisement (Please continue reading this article)
Scientists have many clues that hint at this series of events, such as the discovery of a neutron star in the Crab Nebula left behind by a stellar explosion 1,000 years ago, but we have never seen the real-time process of a supernova explosion creating a dense object.
In May 2022, South African amateur astronomer Berto Monard discovered supernova SN 2022jli in the spiral arm of the nearby galaxy NGC 157, 75 million light-years away, attracting the attention of two different teams from the Weizmann Institute of Science and Queen’s University Belfast The team used the Very Large Telescope (VLT) and the New Technology Telescope (NTT) to observe the aftermath of the supernova explosion, and for the first time directly found evidence of the dense objects it left behind.
The brightness of most supernovae will gradually disappear over time after the explosion, that is, the explosion “light curve” will steadily and gradually decrease. But SN 2022jli behaves very strangely. Its overall brightness decline is not smooth, but oscillates up and down every 12 days or so.
Advertisement (Please continue reading this article)
Both teams believe that the presence of more than one star in the system where SN 2022jli appears can explain this behavior. One of the stars survived the explosion of the companion star, and now the two continue to orbit each other.
▲ The SN 2022jli supernova event occurred in a system with another star orbiting each other. (Source:European Space Agency）
As the researchers gathered more data, they discovered periodic movements of the system’s hydrogen gas, gamma ray bursts, and put all the clues together to conclude that the companion star was rich in hydrogen when it interacted with material thrown off during the supernova explosion. The atmosphere becomes fluffier than usual. Then the dense objects left behind by the explosion will steal hydrogen gas as they quickly pass through the companion star’s atmosphere in orbit, forming a hot material disk around themselves. This periodic material stealing behavior releases a large amount of energy, causing regular changes in the observed brightness.
Although the research team cannot observe light from the compact object itself, the energy accretion behavior can only come from an invisible neutron star or black hole. If new research in the future confirms the existence of black holes or neutron stars in this system, it will be possible to further unravel the exact nature of compact objects and the outcome of this system.
The two papers were published in the journals “Nature” and “The Astrophysical Journal Letters” respectively.
(Source of first picture:European Space Agency）
