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STAG Research CentreNews

Black hole vanishing act offers new insight into universe's mysteries

Published: 14 October 2020
Black hole
A streak of star debris falls into the black hole. Illustration credit: NASA/JPL-Caltech

The mysterious disappearance of a black hole some 300 million light-years from Earth may have been caused by a runaway star being torn apart in a new space phenomenon.

An international team of astronomers, including Dr Poshak Gandhi and Dr Diego Altamirano from the University of Southampton, first discovered a striking variation of the accreting black hole in 2018 and have conducted 15 months of observations to understand the cosmic riddle.

Publishing their findings in the Astrophysical Journal Letters, the team hypothesise that the disappearance of light from 1ES 1927+654 was caused by fast-moving debris from a star crashing through the disk of gas feeding the black hole.

"The astronomy group at Southampton has long expertise on studies of growing supermassive black holes, but this particular one is pretty unique," Poshak says. "It changed in brightness by a factor of more than 10,000 in just a few months, first fading away, and then rebounding to become even brighter than before. This is pretty unprecedented for such cosmic monsters.

"Our best theories suggest that this was the result of some cataclysmic event. For instance, it is possible that an entire star was ripped to shreds when it happened to venture close to the black hole, disrupting the black hole growth briefly, before being consumed by it. Not many such events are known, especially ones showing such dramatic changes."

Supermassive black holes are located at the centre of nearly every galaxy in the universe, with masses millions or billions of times greater than our Sun. The 2020 Nobel Prize for Physics was awarded to three scientists whose body of work solidified the idea that these mysterious monsters must be real.

Black holes don't emit or reflect light but can still be studied by observing the X-ray glow of ultrahot particles of gas being drawn into the region of space. This ultrahot gas can sometimes brighten or dim by factors of a few as the black hole feeds, but this is only a fraction of the 1ES 1927+654 event.

Dr Claudio Ricci, lead author and Assistant Professor at Diego Portales University in Santiago, Chile, says: "We just don't normally see variations like this in accreting black holes. It was so strange that at first we thought maybe there was something wrong with the data. When we saw it was real, it was very exciting. But we also had no idea what we were dealing with; no one we talked to had seen anything like this."

"What struck me was not only the rebound but that it steadily but surely approached a high constant level of brightness," Poshak adds. "This tells us that this specific level must be important.

"I believe the source is approaching a finely balanced state, where its growth is being self-regulated to maintain such a constant level. Understanding this self-regulatory mechanism can teach us a lot about how the majority of black holes in the cosmos grow."

The international study monitored the black hole using NASA's Neutron star Interior Composition Explorer (NICER), an X-ray telescope aboard the International Space Station. In total, NICER observed the system 265 times with additional observations of the system undertaken by NASA's Neil Gehrels Swift Observatory and Nuclear Spectroscopic Telescope Array (NuSTAR) and the ESA (the European Space Agency) XMM-Newton observatory.



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