In October 2018, astronomers detected the bright glow of a star torn apart by a black hole 20 million times larger than our sun 665 million light-years away – the so-called “tidal disturbance event(TDE) dubbed AT2018hyz. But other than that, the event seemed unremarkable, and after a few months of observing the black hole in visible light, the TDE faded, and astronomers continued. But AT2018hyz had a surprise in store. After nearly three years, the black hole suddenly came back to life, baffling astronomers, according to A new paper Published in The Astrophysical Journal.
“This totally surprised us—nobody had ever seen anything like this,” co-author said Yvette Sindis From the Harvard-Smithsonian Center for Astrophysics. She likened a black hole’s unusual feeding behavior to “burping” after eating a heavy meal. “It’s as if this black hole has suddenly started to burp a bunch of material from the star that ate it years ago.” This indicates that delayed flow is more common than astronomers previously expected. The group will continue to monitor TDE as it develops, and is conducting a systematic study of a much larger sample of TDEs.
as we are I mentioned earlierIt is a common misconception that black holes behave Like cosmic vacuum cleaners, greedily absorb any substance in their surroundings. In fact, only things beyond the event horizon – including light – are swallowed up and cannot escape, although black holes are also chaotic eaters. This means that part of the body substance is already expelled in a strong jet.
In a TDE, the star (or “spaghetti”) is sliced by the strong gravitational forces of a black hole outside the event horizon, and a portion of the star’s original mass is violently ejected outward. This, in turn, can be formed rotating ring of the material (aka Accumulation disk) around the black hole emitting powerful X-rays and visible light. Jets are one way astronomers can indirectly infer the existence of a black hole. Outflow emissions usually occur shortly after TDE.
When AT2018hyz was first detected, and radio telescopes did not pick up any signatures of the emission of streaming material for the first few months. According to Cendes, that’s true for about 80 percent of TDEs, so astronomers have moved on, preferring to use precious telescope time to get hold of more interesting objects. But last June, Cendes and her group decided to return to several TDEs over the past few years that had shown no emissions before, using radio data from the Very Large Array (VLA). And lo and behold, AT2018hyz was lighting up the sky once again.
“We’ve been studying TDE with radio telescopes for more than a decade, and we sometimes find that it fluoresces in radio waves as it spews material out as a black hole consumes the star for the first time,” Co-author Edo Berger said:, an astronomer at Harvard University and the Center for Astrophysics. “But at AT2018hyz, there was radio silence for the first three years, and now it’s dramatically lit to become one of the brightest radio TDEs ever.”
The next step was to advance what is known as “estimated time to output” on several different telescopes across a wide spectrum of wavelengths. “When you find something so unexpected, you can’t wait for the regular cycle of telescope proposals to observe it,” Cyndis said. Those requests were immediately accepted, giving the team data from the VLA, the ALMA observatory in Chile, MeerKAT in South Africa, the Australian Telescope Compact Array (ATCA) in Australia, as well as the Chandra X-Ray Space Observatory and Neil Geirels Swift Observatory.
Analysis of all that data revealed that AT2018hyz was spewing material at a whopping 1.4 millijanskiy at 5 GHz. “For those who don’t talk on radio, this is Hella Bright!” Cyndis tweeted In an explanatory series last June when the initial version came out, called “The greatest discovery of my life. This is his Start Seen before from TDE, it certainly wasn’t a few years late. (Fun fact: Cendes and her husband aka AT2018hyz Jetty—an abbreviation for “Jetty McJetFace.”)
TDE was an ongoing event as recently as last April. “We think this is stellar material that was present in an accretion disk after it shredded,” Cyndis tweeted yesterday. But why it took two years for this crazy influx to happen is a mystery.”
One possibility, according to Cendes, is that the outflow density has suddenly changed, but the data does not support this. It also doesn’t support the possibility of an aircraft soon after TDE, but astronomers didn’t spot it right away because it wasn’t aimed at Earth. The light increased very quickly. Cendes also considered the possibility of separate outflows interacting in an unusual way, but concluded that it’s not a likely scenario either.
“The most likely scenario is something called a ‘change of state,’ where the accretion disk around the black hole moves into another type of outflow,” Cyndis tweeted. “We see these around the smaller black holes in our galaxy with donor stars giving them material called X-ray binaries. So, if these changes can happen in stellar-sized black holes in our galaxies, why not around supermassive black holes that got an injection? From a substance from a star?”
But if that’s the case, there must be a significant excess of X-rays – and the data don’t show that either. “Where does that leave us? We don’t know!” Cyndis concluded. “What were we? an act I know AT2018hyz is doing something unexpected and unprecedented in a black hole, and we will continue to monitor it with all we have. We hope the additional notes will help us unravel the mysteries.”
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