What was that? Mystery of the double event of tidal disruption

A supermassive black hole at the center of a galaxy 408 million light-years distant from us has produced two very similar flares almost two years apart. Scientists believe it may be a rare phenomenon — a double tidal disruption event.

A double tidal disruption event. Source: phys.org

Double flare in a distant galaxy

Black holes, which are located in the centers of galaxies, often show themselves with extremely powerful flares, which in their brightness exceed even supernovae. These are tidal disruption events that are still not well understood. However, scientists have recently reported that they have recorded the same phenomenon, only paired.

In general, tidal disruption events are acts of star death. Each of them is unique in its own way, but they have been observed more than once. The event, which was detected in 2022 by the ASAS-SN automatic system near the black hole ASASSN-22ci, also looked quite ordinary at first. Just another star in the WISEA J122045.05+493304.7 galaxy, 408 million light years away from us, carelessly approached the monster at its center and was blown to pieces.

However, 720 days later, the Zwicky Transient Observing Facility and the Asteroid Terrestrial Impact Last Alert System (ATLAS) detected a second flare near the same black hole, very similar to the first. However, both of them looked pretty normal.

Double event of tidal disruption

Scientists suspect that in this case they are dealing with a double tidal disruption event. A black hole usually destroys only one star at a time. However, a pair of luminaries is involved about once every 20 tidal destruction events. 

Judging by the power of both flares, they should have involved stars with masses comparable to the Sun. But the black hole ASASSN-22ci is about 3 million times heavier than it, meaning it can be compared to Sagittarius A* at the center of the Milky Way. 

However, it is incorrect to assume that in this case the two flares correspond to two separate stars. The researchers believe that things happened in a different scenario. At the moment of the first flare, the black hole ripped apart one of the stars, at which point the second received an incredibly powerful acceleration that pushed it away, but not all the way out.

The star could not leave the black hole’s gravitational zone at all and moved to an eccentric orbit, which after 720 days brought it back to the hidden monster. It tried to tear it apart again, but calculations show that in such a scenario, the tidal destruction should only be partial. At the same time, a star may even survive several such cycles.

Waiting for the third flare

Based on all these models, scientists expect a third flare around February 4, 2026. This would confirm that they were right. It would allow them to study the amazing process of destruction of the double system, which should end with the complete destruction of the second luminary as well.

However, a third flare may not occur. It is quite possible that the star was already destroyed during the second tidal destruction event. This possibility cannot be ruled out. Finally, there is a possibility, although a very small one, that scientists have actually misinterpreted all of these events.

It’s quite possible that it wasn’t a binary system. Just two separate stars of roughly the same mass carelessly approached the black hole in a short period of time and were destroyed by it. Then waiting for the third outbreak is also futile.

According to www.space.com

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