Astronomers detect the oldest black hole ever found

Friday, 19 January, 2024

Astronomers detect the oldest black hole ever found

An international team of researchers, led by the University of Cambridge, has used the James Webb Space Telescope (JWST) to locate the oldest black hole ever known, dating from just 400 million years after the Big Bang (the latter having occurred more than 13 billion years ago). Detected in the host galaxy GN-z11 and documented in the journal Nature, the black hole is surprisingly massive — a few million times the mass of our Sun — with its existence so early in the universe challenging our assumptions about how black holes form and grow.

According to standard models, supermassive black holes form from the remnants of dead stars, which collapse and may form a black hole about a hundred times the mass of the Sun. If it grew in an expected way, this newly detected black hole would take about a billion years to grow to its observed size. However, the universe was not yet a billion years old when this black hole was formed.

“It’s very early in the universe to see a black hole this massive, so we’ve got to consider other ways they might form,” said lead author Roberto Maiolino, from Cambridge’s Cavendish Laboratory and Kavli Institute for Cosmology. It may have simply been ‘born big’ or its size may be due to its ability to eat matter at a rate that’s far higher than had been thought possible. For while this black hole, like others, devours material from its host galaxy to fuel its growth, it has been found to gobble matter much more vigorously than its siblings at later epochs.

“Very early galaxies were extremely gas-rich, so they would have been like a buffet for black holes,” Maiolino noted.

Black holes cannot be directly observed; instead they are detected by the tell-tale glow of a swirling accretion disc, which forms near the edges of a black hole. The gas in the accretion disc becomes extremely hot and starts to glow and radiate energy in the ultraviolet range. GN-z11 glows from having such an energetic black hole at its centre; indeed, the black hole is likely harming the development of this compact galaxy, which is around a hundred times smaller in size than the Milky Way. This is because when a black hole consumes too much gas, it pushes the gas away like an ultrafast wind; this ‘wind’ could stop the process of star formation, slowly killing the galaxy — as well as inadvertently cutting off the black hole’s source of ‘food’.

Maiolino said that the sensitivity of JWST means that even older black holes may be found in the coming months and years. He and his team are hoping to use future observations from JWST to try to find smaller ‘seeds’ of black holes, which may help them untangle the different ways that black holes might form: whether they start out large or they grow fast.

“It’s a new era: the giant leap in sensitivity, especially in the infrared, is like upgrading from Galileo’s telescope to a modern telescope overnight,” he said. “Before Webb came online, I thought maybe the universe isn’t so interesting when you go beyond what we could see with the Hubble Space Telescope. But that hasn’t been the case at all: the universe has been quite generous in what it’s showing us, and this is just the beginning.”

This is a modified version of a news item published by the University of Cambridge under CC BY-NC-SA 4.0. This version is similarly licensed under CC BY-NC-SA 4.0.

Image caption: The GN-z11 galaxy, taken by the Hubble Space Telescope. Image credit: NASA, ESA, and P Oesch (Yale University).

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