A group of astronomers and researchers from Tel Aviv University observed a repeated powerful flare sent by a star, that was being swallowed by a black hole.
An almost identical outburst, dubbed AT 2022dbl, was seen in the same area of space two years ago. This is the first confirmed case of a star experiencing initial contact with a supermassive black hole and returned for a second contact.
This challenges the conventional wisdom about tidal destruction and raises the possibility that these spectacular outbursts may be just the beginning of a more complex cosmic process. The study was led by Dr. Lydia Macrigianni, a former researcher at Tel Aviv University who is currently working at Lancaster University in the UK, and Professor Iyer Arkavi from the Department of Astrophysics at Tel Aviv University.
As the researchers explain, in the center of every large galaxy there is a black hole with a mass millions and billions of times greater than the solar mass. A similar supermassive black hole exists in the Milky Way galaxy. Physicists received the Nobel Prize for its discovery in 2020. However, it is still not fully understood how these supermassive black holes are formed and how they affect the galaxies in which they are located.
A black hole is a region of space where gravity is so strong that even light cannot escape. A supermassive black hole in the center of the Milky Way was discovered due to the movement of stars in its vicinity. But in other, more distant galaxies, such motion cannot be detected.
However, once every 10 thousand —100 thousand years, a star comes too close to a supermassive black hole in the center of the galaxy and is torn apart by gravity. The black hole swallows up half of the star, and the other half is ejected outward.
The substance that falls on the black hole begins to rotate in a circle, just like water flowing down a drain. However, near black holes, the speed of rotation of the substance approaches the speed of light, the substance heats up and emits brightly. A star like this can «illuminate the» black hole for several weeks or months, allowing astronomers to study this process.
However, such flares began to behave differently than expected. Their brightness and temperature were much lower than predicted. After roughly 10 years of trying to understand the cause, AT 2022dbl may provide the answer. The recurrence of the outburst almost 2 years later indicates that at least the first outburst was the result of a partial destruction of the star. At the same time, most of it was preserved and re-approached the black hole.
“The question now is whether we will see a third outbreak in another two years, in early 2026. If we see a third outbreak — this would mean that the second flare was also a partial destruction of the star. So, perhaps all such flares, which we have been trying to interpret for 10 years as a complete destruction of the star, are not what we thought,” — notes Professor Iyer Arkavi/
If the third outburst does not occur, the second outburst could have led to the complete destruction of the star. This means that partial and total destruction look almost identical, as the research team of Professor Zvi Piran of the Hebrew University had predicted before the discovery.
The results are published in the journal The Astrophysical Journal Letters
Source: SciTechDaily
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