Astronomers have found six ancient galaxies surrounding a supermassive black hole from when the Universe was less than a billion years old. Researchers say this is the first time such a close grouping has been seen so soon after the Big Bang.
The finding helps to better understand how supermassive black holes, one of which exists at the centre of our Milky Way, formed and grew to their enormous sizes so quickly. It also supports the theory that black holes can grow rapidly within large, web-like structures which contain plenty of gas to fuel them, according to the astronomers.
“This research was mainly driven by the desire to understand some of the most challenging astronomical objects – supermassive black holes in the early Universe,” said Marco Mignoli, an astronomer at the National Institute for Astrophysics (INAF) in Bologna, Italy, and lead author of the study.
“These are extreme systems and to date we have had no good explanation for their existence.”
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The observations, made by the European Southern Observatory’s (ESO) Very Large Telescope (VLT), revealed several galaxies surrounding a supermassive black hole, all lying in a cosmic “spider’s web” of gas extending to more than 300 times the size of the Milky Way.
“The cosmic web filaments are like spider’s web threads,” Mignoli added. “The galaxies stand and grow where the filaments cross, and streams of gas – available to fuel both the galaxies and the central supermassive black hole – can flow along the filaments.”
According to the study, published in the Astronomy and Astrophysics journal, the light from this large web-like structure, with its black hole one billion times the mass of the Sun, has travelled to Earth from a time when the Universe was only 900 million years old.
There is a lot that astronomers don’t yet know about supermassive black holes. “Our work has placed an important piece in the largely incomplete puzzle that is the formation and growth of such extreme, yet relatively abundant, objects so quickly after the Big Bang,” said Roberto Gilli, also an astronomer at INAF in Bologna.
It is thought the first black holes, believed to have formed from the collapse of the first stars, must have grown very fast to reach a billion solar masses within the first 900 million years of the Universe’s life.
Astronomers have struggled to explain how sufficiently large amounts of “black hole fuel” could have been available to enable these objects to grow to such enormous sizes in such a short time.
However, they suggest the new-found structure offers a likely explanation – the web-like structure and the galaxies within it contain enough gas to provide the fuel that the central black hole needs to quickly become a supermassive giant.
“We believe we have just seen the tip of the iceberg, and that the few galaxies discovered so far around this supermassive black hole are only the brightest ones,” said co-author Barbara Balmaverde, an astronomer at INAF in Torino, Italy.
Reader Q&A: Do black holes collapse?
Asked by: Patricia Rodrigues, King’s Lynn
The Schwarzschild radius (event horizon) of a black hole is sometimes thought of as the black hole’s ‘size’. It is proportional to mass, which means that more massive black holes have bigger Schwarzschild radii.
Left alone, black holes lose mass due to ‘Hawking radiation’, so that their event horizons are slowly shrinking. A typical black hole would take many billions of times the age of the Universe to completely ‘evaporate’ and disappear.
But, the interior of the black hole, or its ‘singularity’ (the point at which all the black hole’s matter is concentrated) has already reached the limit of its density and cannot ‘collapse’ any further.
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