A look at the formation of a super-compact celestial body: Astronomers have observed a supernova explosion in a binary star system in which one partner transformed into a neutron star or a black hole. This is the first direct evidence that these special celestial bodies can emerge from a supernova, say the scientists.
Astronomical bangs accompanied by dazzling light: Type 2 supernova explosions occur when a massive star has used up its supply of fuel and collapses under its own weight. This releases enormous amounts of energy, which are discharged with gigantic force. Astronomers assume that after this form of supernova explosion, an extremely compact remnant is created from the star: If it was particularly massive, it turns into a black hole – an object with such a strong gravitational effect that not even light can escape . With a slightly lower initial mass, however, a neutron star is formed – also an extremely dense celestial body.
Astronomical observations have already proven the formation of these super-compact objects after supernova explosions. However, the focus was on the remnants in a later phase – the process itself has not yet been observed in real time. “In our work we are now making such a direct connection,” says Ping Chen from the Weizmann Institute of Science in Rehovot. He is the first author of the publication in Nature magazine – one of two studies reporting the discovery. Both are based on the discovery of an amateur astronomer: In May 2022, Berto Monard recognized the glow of a supernova in the galaxy NGC 157, 75 million light-years away. Two teams of astronomers then set their sights on this stellar explosion, designated SN 2022jli.
“Flickering” after the supernova
The astronomers independently discovered a peculiarity that led to the two publications. After the explosion, the brightness of most supernovae usually decreases steadily – there is a uniform decrease in the light curve. But that wasn’t the case with SN 2022jli: although the overall brightness faded, SN 2022jli flickered slightly about every twelve days. “In the data we see a repeating sequence of brightening and dimming,” says Thomas Moore from Queen’s University, Belfast – lead author of the second study, published in the Astrophysical Journal. “This is the first time that repeated periodic oscillations over many cycles have been detected in the light curve of a supernova,” the study says.
Both teams of astronomers came to the same explanation for this phenomenon: they believe that the presence of more than one star in the SN 2022jli system caused the effect. In other words: the supernova took place in a binary star system. The special thing was that the companion star survived the explosion of its partner. Apparently the remnant of the supernova and the companion star continue to orbit each other, the astronomers explain. The authors of the Nature publication were also able to provide more detailed information based on data from a number of measuring instruments, including the X-Shooter at the Very Large Telescope (VLT) of the European Southern Observatory (ESO) in Chile.
A neutron star or black hole makes itself felt
In the data, the researchers found evidence of periodic movements of hydrogen gas and bursts of gamma rays in the system. They can be explained by development processes after the supernova: According to this, the hydrogen-rich atmosphere of the companion star expanded as it interacted with the material that was ejected during the explosion. Through this “bubble,” the compact remnant of the exploded partner then made itself felt: Whenever it raced through the atmosphere of the companion star in its orbit, it pulled gas towards itself and thereby formed a hot, bright disk of matter around itself. This periodic effect then became noticeable in the observations as a regular fluctuation in brightness, the astronomers explain.
The compact object that grabs the matter from the bloated atmosphere of the companion star cannot be seen directly. But based on its effect, the researchers conclude that it must be an invisible neutron star or a black hole. For the first time, a direct connection has now been shown between the explosive death of a massive star and the formation of the most compact objects in the universe.
The exciting system should now remain the focus of astronomy. It is possible that even more precise information about the nature of the compact object or the further development of the binary star system can be identified. Among other things, the astronomers are hoping for the increased view that could be made possible by ESO’s Extremely Large Telescope, which is currently under construction and is scheduled to be put into operation before the end of this decade.
Source: ESO, specialist article: Nature doi: 10.1038/s41586-023-06787-x
https://www.nature.com/articles/s41586-023-06787-x
The Astrophysical Journal Letters, doi: 10.3847/2041-8213/acfc25