Astronomers have found evidence that supermassive black holes can grow quickly by suddenly devouring large amounts of gases present in their surroundings.
Supermassive black holes usually sit at the heart of galaxies, and are millions to billions times larger than the Sun. Until recently, astronomers were unsure about how these supermassive black holes grow to their size. In general, astronomers believe that they do so by consuming stars and other material that comes too close to them.
In February 2017, astronomers observed an event, dubbed AT 2017bgt, which was initially thought to be a "star swallowing" event or a "tidal disruption" event. The event was extraordinary as the radiation emitted around the black hole suddenly became 50 times more intense, compared with the observations starting in 2004.
The event was further investigated by a group of astronomers, who using three telescopes, including the NICER, to observe the event. They found that the event emitted a spectrum of light that had not been observed before in such a context.
After detailed investigation, researchers arrived at the conclusion that AT 2017bgt was not a stellar burp, and it actually represented a new way of "feeding" black holes, where these massive monsters are triggered to suddenly start consuming huge amounts of gas in their surroundings.
The study was led by Dr Iair Arcavi and Dr Benny Trakhtenbrot, both of Tel Aviv University's (TAU) Raymond & Beverly Sackler School of Physics and Astronomy, and also involved researchers from the US, UK, Chile, and Poland.
"We followed this event for more than a year with telescopes on Earth and in space, and what we saw did not match anything we had seen before," said Arcavi.
"We are not yet sure about the cause of this dramatic and sudden enhancement in the black holes' feeding rate," says Trakhtenbrot.
"There are many known ways to speed up the growth of giant black holes, but they typically happen during much longer timescales."
Researchers have also identified two other separate events, where black holes were found to have "switched on" and to exhibit the same emission properties as AT 2017bgt.
The team hopes to track other, similar events in future to understand the reasons behind the sudden speed-up in the growth rate for black holes. Astronomers believe that could help them solve the mystery of how these black holes are form in the universe.
The findings of the study are published in journal Nature Astronomy.
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