A black hole ejected the star a few years after swallowing it

A black hole that swallowed a star a few years ago has now ejected its material in an unexpected event.

BingMag.com A black hole ejected the star a few years after swallowing it

A black hole that swallowed a star a few years ago has now ejected its material in an unexpected event.

It was in October 2018 that astronomers observed the bright flare of a star being torn apart by a black hole 20 million times the mass of the Sun, 665 million light-years away. The event, referred to as a "Telical Disturbance Event" (TDE) or "Tidal Disturbance Event", was named AT2018hyz. This TDE faded. Astronomers also turned their gaze to other objects, but they did not know that a surprise was waiting for AT2018hyz. According to a new article published in the Astrophysical Journal, almost three years later, the black hole suddenly came back to life, puzzling astronomers.

Yvette Cendes, a One of the authors of this article from the Harvard-Smithsonian Center for Astrophysics considered this event surprising and unique. He likened the black hole's unusual feeding behavior to belching after a heavy meal. It's as if the black hole has started to suddenly regurgitate a bunch of stellar material that it ate years ago.

This suggests that delayed ejection of material from a black hole is more common than astronomers expected. The group will continue to monitor these TDEs, and a systematic study of a much larger sample of TDEs is underway. It strongly sucks the materials around them. But in fact, only things that pass through the "Event Horizon", including light, will be swallowed and will not be able to escape. Although even black holes chaotically swallow material, some of it is ejected as a powerful jet. See

In a TDE, a star becomes spaghetti-like by the powerful gravitational forces of the black hole outside the event horizon, and part of the star's original mass is violently ejected. This process, in turn, can form a rotating ring of matter, known as an accretion disk, around the black hole, which emits powerful X-rays and visible light. It is based on these jets that astronomers can indirectly understand the existence of a black hole.

Their emission usually occurs immediately after the TDE event, but after the discovery of AT2018hyz for the first time, radio telescopes did not show any signs for the first few months. They did not find material from the emission of the outflow stream. According to Sandes, this happens in 80% of tidal disturbances, so astronomers preferred to use the telescope's precious time to observe potentially more interesting objects.

In June last year, Sandes and His team decided to use Very Large Array (VLA) radio data to examine several TDE events from the past few years that had previously shown no sign of emitting material, and found that AT2018hyz is shining brightly in the sky again.

Edo Berger, one of the authors of this paper and an astronomer at Harvard University, said about this event: "For more than a decade, we have been studying latitudinal disturbances with radio telescopes, and sometimes we see them glow in the radio spectrum by ejecting material. . But for the first three years of AT2018hyz, there was radio silence, and now it has become remarkably bright and one of the brightest radio events of its kind.

BingMag.com A black hole ejected the star a few years after swallowing it

Light intensity curve of AT2018hyz
Credit: Y. Cendes et al., 2022

With this rare observation, Scientists were given dedicated time to observe it with a telescope and thus managed to record data using the VLA, the ALMA observatory in Chile, the MeerKAT in South Africa, the Australian Compact Telescope Array (ATCA) ) as well as the Chandra X-ray Space Observatory and the Nile Girls Swift Observatory.

Analysis of all these data showed that AT2018hyz emits material at a frequency of 1.4 milliyansk at 5 GHz. An amount that, according to Sandes, is too bright for outside the field of radio astronomy.

This TDE was happening even last April. "We think this is stellar material that was in an accretion disk after it fragmented," Sindes recently tweeted. But why it took two years for this crazy outflow to happen is a mystery.

One possibility, he says, is that the density of the outflow suddenly changed, but the data doesn't show that. These data also do not support the possibility that the jet stream existed immediately after the TDE, but because it was not directed towards the Earth, successful astronomers It has not been identified. The light of this event increased very quickly. Sandos also considered the possibility that two separate outflow jet streams might have interacted in an unusual way, but ultimately found that to be an unlikely scenario.

He tweeted: The most likely scenario. There's something called state transition, where the accretion disk around the black hole turns into a different kind of outflow. "We see these around smaller black holes in our galaxy, where stars dump material into the black hole, which is ejected as X-ray binaries." For as many as stars to occur in our galaxies, why not around supermassive black holes fed by streams of stellar material?" They do not show this either. "Where does this mystery end? We don't know! But we do know that AT2018hyz is doing something unexpected that has never been seen before in a black hole. So we'll continue to monitor it with everything we have."

Cover photo: A graphic of a tidal disruption event in which a black hole spaghetti-likely eats a star.
Credit: DESY, Science Communication Lab

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