Israeli astronomers have for the first time interpreted a particular luminous event that occurred in February 2017 as the beginning of the “feeding” of a black hole. A phenomenon predicted by a theory since the 1980s, but which for the time being had never been confirmed by observations.
Monsters do not all eat fresh flesh… For some, not least, a cloud of gas is enough. The identity of these singular ogres: supermassive black holes.
In a study published in the journal Nature Astronomy, Israeli researchers reveal how a supermassive black hole begins to devour the gas around it. To do this, the scientists began their work by studying an event that occurred in February 2017. Called AT 2017bgt, it was captured by the All Sky Automated Survey for Supernovae, a device consisting of two separate telescopes and intended to search for possible new supernovae.
Initially, some scientists believed that AT 2017bgt could be the manifestation of a star’s “swallowing” by a supermassive black hole, otherwise known as a “tidal disruption“. But by looking more closely at the data collected by the All Sky Automated Survey for Supernovae, the Israeli team came to another conclusion: AT 2017bgt was actually the manifestation of “feeding” a black hole.
“The sudden brightening of AT 2017bgt was reminiscent of a tidal disruption event, but we quickly realized that this time there was something unusual: the first clue was an additional light component, which had never been observed in the case of tidal disruption events,” says the first author of the study Benny Trakhtenbrot, of the TAU’s Raymond & Beverly Sackler School of Physics and Astronomy. An unusual event, as confirmed by one of the co-authors of the study, Iair Arcavi, responsible for data acquisition:
“We have been following this event for over a year with telescopes on Earth and in space, and what we have seen is nothing we have seen before.”
One of the members of the Israeli team, Professor Hagai Netzer, was quick to connect these intriguing observations with theories he had constructed some forty years ago. “We predicted in the 1980s that a black hole swallowing gas in its vicinity could produce the luminous components observed today. With this new result, this is the first time the process is observed in practice,” says Hagai Netzer.
After discovering two other events comparable to AT 2017bgt, astronomers now dream of being able to discover many more thanks to the advanced instruments now available to them: “We hope to detect many more events of this type, and follow them as this is the only way to complete our portrait of the growth of black holes, to understand what is causing them to accelerate, and perhaps to finally solve the mystery urrounding] the way these monsters giants are formed,” Iair Arcavi concludes.
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