Astronomers spotted a zombie star consuming its companion for the first time

For the first time, scientists have seen a dead star that exploded in a supernova continue to behave as if it were still alive. After its death, it found itself in the orbit of a companion star and absorbed its gas.

This is the subject of two separate studies, one of which was published in The Astrophysical Journal and the other appeared in the scientific journal Nature. It is known that when a star becomes a supernova, its explosion spews light and energy throughout the universe, upsetting the delicate cosmic balance in the star system. Eventually, such a star turns into a neutron star or a black hole, two types of dense objects that were once the core of a massive star.

However, scientists have only guessed at what exactly happens to a star during the transition period immediately after a supernova flare. Now they have an answer.

In 2023, a team of researchers led by astrophysicist Thomas Moore of Queen's University Belfast observed a supernova explosion in the galaxy NGC 157. They noticed that the bright light from the explosion faded as expected but then continued to flash at regular intervals, gradually dimming.

In parallel, another team of scientists also saw this phenomenon, but through infrared telescopes. Astrophysicist Ping Chen of the Weizmann Institute in Israel and his team were trying to measure how hydrogen gas flows in and around the central supernova explosion for their study. It was then that they noticed that bursts of hydrogen gas movement coincided with flashing flashes of light, and with powerful bursts of gamma rays.

According to Inverse, Chen believes they were observing a neutron star or black hole at the heart of a supernova, which is part of a binary pair of stars orbiting a common center of gravity. The bright flashes of light that Moore and his team saw, as well as the gamma-ray bursts that Chen and the team saw, could have been caused by hydrogen gas falling onto the extremely dense remnants of the dead star.

Scientists know that the most massive stars in the Universe often form pairs with a common center of gravity. But the tendency of such stars to die explosively usually leads to a sad fate for the "partner."

Chen noted that in most cases, a supernova explosion "destroys a binary system." This means that the exploded star throws most of its mass into space, so the core that remains after the explosion no longer has the gravitational force to keep the companion star close. So this companion will most likely just be ejected into space.

But in the case observed by both groups of scientists, something surprising happened. Moore suggests that the supernova explosion spawned a neutron star, pushing it into a dangerously close orbit around the surviving companion star. As a result, a strange tandem was formed in which the neutron star circling the companion snatches pieces of gas from its outer layers with each pass. In effect, the dead star is stealing pieces of its own shed skin and eating them.

Neither Chen's team nor Moore and his colleagues can see the core of the dead star and say for sure whether it is a black hole or a neutron star. The reason for this is that this core is hidden by the light of its satellite and a cloud of hot gas released by the supernova.

Scientists hope that they will be able to unravel the mystery of what they saw in the future when they observe new supernova explosions with more powerful telescopes that will allow them to better see the flow of hydrogen during these events and estimate how massive the dead stellar core is. It is the answer to the latter question that will help determine whether a black hole or a neutron star has formed.

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