Supermassive black hole at heart of ancient galaxy ‘far larger than expected’
A supermassive black hole discovered at the heart of an ancient galaxy is five times larger than expected for the number of stars it contains, astronomers say.
Researchers spotted the immense black hole in a galaxy known as GS-9209 that lies 25bn light-years from Earth, making it one of the most distant to have been observed and recorded.
The team at Edinburgh University used the James Webb space telescope (JWST) to observe the galaxy and reveal fresh details about its composition and history.
Dr Adam Carnall, who led the effort, said the telescope – the most powerful ever built – showed how galaxies were growing “larger and earlier” than astronomers expected in the first billion years of the universe.
“This work gives us our first really detailed look at the properties of these early galaxies, charting in detail the history of GS-9209, which managed to form as many stars as our own Milky Way in just 800m years after the big bang,” he said.
Carnall said the “very massive black hole” at the centre of GS-9209 was a “big surprise” that lent weight to the theory that such enormous black holes are responsible for shutting down star formation in early galaxies.
“The evidence we see for the supermassive black hole was really unexpected,” said Carnall. “This is the kind of detail we’d never have been able to see without JWST.”
The GS-9209 galaxy was discovered in 2004 by Karina Caputi, a former PhD student at Edinburgh who is now a professor of observational cosmology at the University of Groningen in the Netherlands.
While GS-9209 has roughly as many stars as our home galaxy, with a combined mass equal to 40bn suns, it is only one-tenth the size of the Milky Way. It is the earliest known example of a galaxy that has stopped forming stars, the researchers said.
Supermassive black holes can shut down star formation because their growth releases huge quantities of high-energy radiation, which can heat up and drive gas out of galaxies. Galaxies need vast clouds of gas and dust to collapse under their own gravity, thereby creating new stars.
“The fact [that the black hole] is so massive means it must have been very active in the past, with lots of gas falling in, which would have shone extremely brightly as a quasar,” Carnall said. “All that energy spewing out from the black hole in the centre of the galaxy would have seriously disrupted the whole galaxy, stopping gas from collapsing to form new stars.”
More details are published in Nature.