The captured star has had several close encounters with a supermassive black hole in a galaxy far, far away – and may even have survived matter being torn apart by the massive gravitational tidal forces.
destroy a star by the gravitational forces of supermassive black hole It is a violent affair known as a tidal disturbance event (TDE). Gas is stripped from the star and undergoes a “spaghettichen” process, during which it is shredded and spilled into streams of hot material that swirl around the star. Black hole, forming a very bright and temporary accretion disk. From our point of view, the center galaxy The supermassive black hole appears to be on fire.
On September 8, 2018, the All-Sky Automated Survey for Supernovae (ASASSN) detected an explosion at the heart of a distant galaxy 893 million light-years away. The missile, classified as AT2018fyk, had all the characteristics of a TDE. Various X-ray telescopes, including NASA telescopes QuicklyEurope XMM-NewtonWith them cute Instrument installed on the International Space Station, Germany AerositaNote that the black hole has brightened greatly. Normally, TDEs show a steady decrease in brightness over several years, but when astronomers looked at AT2018fyk again about 600 days after it was first observed, the X-rays quickly disappeared. Even more puzzling is that the black hole suddenly exploded about 600 days later. What was going on?
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“Until now, the assumption was that when we see the consequences of a close encounter between a star and a supermassive black hole, the result would be fatal for the star, that is, the star would be completely destroyed,” said Thomas Weavers, an astronomer at the European Southern Observatory and author of a new paper on the event, in a statement. “But unlike every other TDE we know of, when we pointed our telescopes again at the same spot several years later, we found that it had flared up again.”
Wevers led a team of astronomers who realized that repeat flares were a signature of a star that survived a TDE and completed another orbit for a second TDE. To fully explain what they were observing, Wevers’ group developed a model of “recurrent partial TDE”.
In their model, the star was once a member of the binary system It passes very close to the black hole at the center of its galaxy. The gravity of the black hole threw one of the stars away, and it turned into a runaway Super speed star Run at 600 miles (1000 km) per second out of the galaxy. The other star has become tightly bound to the black hole, in a 1,200-day elliptical orbit that has brought it toward what scientists call the tidal radius — the distance from the black hole at which the star begins to tear apart. Black hole.
Because the star was not entirely within its tidal radius, only some of its material was stripped away, leaving a dense stellar core that continued in its orbit around the black hole. It takes about 600 days for material extracted from a star by the black hole to form an accretion disk, so by the time astronomers saw the system go up in flames, the star was safe, near the point farthest from its orbit.
But when the star’s core began to approach the black hole again, about 1,200 days after their first encounter, the star began picking up some of its material from the accretion disk, causing a sudden drop in its X-ray emission. “The core goes back into the black hole, it basically steals all the gas out of the black hole by gravity, so there is no matter accumulating, so the system shuts down,” Dheeraj Pasham, study co-author and astrophysicist at MIT, said in a statement. Journalist.
But the black hole gravity He quickly returns the favor, and steals more material from the approaching star. As with the initial encounter, there is a 600-day lag between the star-munching black hole and the formation of the accretion disk, which explains why the X-ray glow flared up at that time.
From the star’s orbit, Wavers’ team estimated the black hole to be about 80 million times the mass of our sun, or about 20 times the mass of the black hole at the center of our planet. Milky WayAnd arch a*.
The Wevers won’t have to wait long to see if the theory turns out to be true. Scientists expect AT2018fyk to darken again in August when the star’s core returns, and to brighten again in March 2025 when new material begins accreting to the black hole.
However, there is a potential complication in how much mass the black hole lost. The amount of mass lost depends in part on the speed of the star’s rotation, which the black hole can affect. If the star was spinning nearly fast enough to break apart, the black hole would easily steal material, adding to the mass loss.
“If the mass loss is only at the 1% level, we would expect the star to survive many more encounters, whereas if it is closer to 10%, the star may have already been destroyed,” said co-author Eric. Coughlin. on the study from Syracuse University in New York, he said in the statement.
Either way, repeat TDEs and partial TDEs provide a rare window into the life of supermassive black holes that we normally can’t detect because they’re asleep. This is important for measuring their mass and determining how black holes evolved, and thus how the galaxy around the black hole also evolved throughout cosmic history.
The results were presented at the 241st meeting of the American Astronomical Society and published in Letters from The Astrophysical JournalBoth on January 12th.
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