A supermassive black hole with millions to billions times the mass of our sun is seen in an undated NASA artist's concept illustration..
(photo credit: REUTERS/NASA/JPL-CALTECH/HANDOUT)
A new Tel Aviv University-led study finds that some supermassive black holes are triggered to grow, suddenly devouring a large amount of gas in their surroundings.
Supermassive black holes weigh millions to billions times more than the sun and lie at the center of most galaxies, one of which is situated in the Milky Way. Their growth reason remains unclear, despite how commonplace they are. Although some may swallow gas in their surroundings and others may suddenly swallow whole stars, no theory explains how they can "switch on" unexpectedly and grow fast for a long period of time.
In February 2017, the All Sky Automated Survey for Supernovae discovered an event known as AT 2017bgt.
This event was initially believed to be a "star swallowing" event, or a "tidal disruption" event, because the radiation emitted around the black hole grew more than 50 times brighter than what had been observed in 2004.
However, after extensive observations using a multitude of telescopes, a team of researchers led by Dr. Benny Trakhtenbrot and Dr. Iair Arcavi, both of TAU's Raymond & Beverly Sackler School of Physics and Astronomy, concluded that AT 2017bgt represented a new way of "feeding" black holes.
"We quickly realized that this time, there was something unusual," said Dr. Trakhtenbrot. "The first clue was an additional component of light, which had never been seen in tidal disruption events."
"We had predicted back in the 1980s that a black hole swallowing gas from its surroundings could produce the elements of light seen here," said Professor Hagai Netzer, also of Tel Aviv University. "This new result is the first time the process was seen in practice."
Three different telescopes were used to observe and analyze by astronomers from the US, Chile, Poland and the UK. One of those telescopes was the new NICER telescope installed on board the International Space Station.
The research team identified two additional recently reported events of black holes "switched on," which share the same emission properties as AT 2017bgt. These three events form a new and tantalizing class of black hole re-activation.
"We are not yet sure about the cause of this dramatic and sudden enhancement in the black holes' feeding rate," concluded Trakhtenbrot. "There are many known ways to speed up the growth of giant black holes, but they typically happen during much longer timescales."
"We hope to detect many more such events, and to follow them with several telescopes working in tandem," said Dr. Arcavi. "This is the only way to complete our picture of black hole growth, to understand what speeds it up, and perhaps finally solve the mystery of how these giant monsters form."
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