Star survives black hole spaghettification
A trapped star has had multiple encounters with a supermassive black hole in a distant galaxy — and may even have survived after material was ripped away by immense gravitational tidal forces.
The destruction of one star by the gravity of a supermassive black hole is a violent affair known as a tidal disturbance (TDE). Gas is ripped from the star and undergoes “spaghettification,” where it is shredded and stretched into streams of hot material that flow around the star. black hole, which forms a temporary and very bright accretion disk. From our point of view, the center of the universe in which the supermassive black hole resides appears to flash.
On September 8, 2018, the All-Sky Automated Survey for Supernovae (ASASSN) spotted an outburst at the core of a distant galaxy 893 million light-years away. Cataloged as AT2018fyk, the torch had all the features of a TDE. Various X-ray telescopes, including NASA’s FastEurope XMM-Newtonthe MORE BEAUTIFUL instrument mounted on the International Space Station and that of Germany ROSITE, saw the black hole brighten dramatically. Usually TDEs show a steady decrease in brightness over several years, but when astronomers looked again at AT2018fyk about 600 days after it was first spotted, the X-rays quickly dissipated. Even more puzzling, about 600 days after that, the black hole suddenly flared up again. What was going on?
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“Until now, the assumption has been that when we see the aftermath of a star meeting a supermassive black hole, the outcome will be fatal for the star, i.e. the star is completely destroyed,” says Thomas Wevers, a astronomer at the European Southern Observatory and an author of new research on the event, said in a pronunciation. “But unlike all the other TDEs we know of, when we pointed our telescopes back at the same location several years later, we found that it had brightened again.”
Wevers led a team of astronomers who realized the repeated flares were the signature of a star that had survived a TDE and completed another orbit only to experience a second TDE. To fully explain what they observed, Wevers’ group developed a model of a “repeating partial TDE”.
In their model, the star was once a member of one binary system which passed too close to the black hole at the center of its galaxy. The gravity of the black hole ejected one of the stars, which turned into a fugitive hypervelocity star racing at 600 miles (1,000 kilometers) per second out of the galaxy. The other star became tightly tethered to the black hole, in a 1,200-day elliptical orbit that brought it toward what scientists call the tidal radius — the distance from the black hole at which a star begins to be torn apart by the gravitational tides that emanate from it. are of the black hole.
Because the star was not completely within the tidal radius, only some of its material was stripped away, leaving a dense stellar core that continued its orbit around the black hole. It takes about 600 days for the material pulled through the star’s black hole to form the accretion disk, so by the time astronomers saw the system flash, the star was safe, near the farthest point of its orbit.
But as the star’s core began to approach the black hole again, about 1,200 days after its first encounter, the star began stealing some of its material back from the accretion disk, causing the X-rays to suddenly fade. “When the core returns to the black hole, it essentially steals all the gas away from the black hole via gravity, and as a result there is no matter to grow on and so the system goes dark,” said Dheeraj Pasham, a co-author of the study and an astrophysicist at MIT, said in the statement.
But that of the black hole gravity soon returns the favor and steals more material as the star approaches. Like the first encounter, there’s a 600-day delay between the black hole snacking on the star and the formation of the accretion disk, which explains why the X-rays turned back on when that happened.
From the star’s orbit, Wevers’ team calculated that the black hole has a mass nearly 80 million times that of our sun, or about 20 times the mass of the black hole at the center of our solar system. galaxy, Sagittarius A*.
Wevers’ team doesn’t have to wait long to find out if the theory is correct. The scientists predict that AT2018fyk will darken again in August, when the star’s core goes round again, and will glow again in March 2025, when new material begins to accrete onto the black hole.
However, there is a possible complication in the amount of mass the star has lost to the black hole. The amount of mass lost depends in part on how fast the star is spinning, which may be affected by the black hole. If the star is spinning almost fast enough to break apart, the black hole will steal material more easily, increasing its mass loss.
“If the mass loss is only at the 1% level, we expect the star to survive many more encounters, while if it’s closer to 10%, the star may have already been destroyed,” said Eric Coughlin, a co-author of the study. author. on the study from Syracuse University in New York, the statement said.
Anyway, TDEs and repeating partial TDEs provide a rare glimpse into the life of supermassive black holes that we normally can’t detect because they’re dormant. This is important to measure their masses and determine something about how the black holes have evolved, and thus how the galaxy around the black hole has also evolved in cosmic history.
The findings were presented at the 241st meeting of the American Astronomical Society and published in The Astrophysical Journal Lettersboth on January 12.
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