Astronomers have discovered a black hole that existed more than 13 billion years ago, when the universe was only 400 million years young. This surprising discovery turns the idea about the formation of massive black holes upside down.
Using the James Webb Space Telescope, astronomers have discovered a black hole at the heart of a galaxy with about a million times the mass of the Sun. This galaxy, called GN-z11, is more than 13 billion light-years away. This means that the telescope sees the system as it looked more than 400 million years after the Big Bang.
Because the galaxy was remarkably bright, astronomers suspected that the light came not only from stars, but mainly from a dining black hole. When black holes absorb gas and dust in their environment, a swirling disk of matter is created that gradually disappears into the black hole. That disk is so hot that it emits bright light.
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So the researchers expected to find a black hole. “But it was surprising to find that this specimen had so much mass so early,” says astrophysicist Roberto Maiolino of the University of Cambridge, who was involved in the discovery, published in Nature. That does not fit the current picture of how black holes are formed.
At the heart of almost all large galaxies lies a supermassive black hole. In current galaxies, such as our own Milky Way, you will find them of millions to even billions of solar masses. Until now, astronomers thought that the ‘seeds’ of this were supermassive stars, which formed shortly after the Big Bang. At the end of their lives, these massive stars collapse into black holes with several tens to hundreds of times the mass of the Sun.
They would then have grown steadily by sucking gas from their galaxy. Every now and then they would have a small growth spurt when they merge with another black hole. But this process would take billions of years, and therefore cannot explain how the massive black hole in the galaxy GN-z11 was formed.
Greedy black hole
A possible explanation is that the supermassive ones did not start out as massive stars that collapsed at the end of their lives, but were born as black holes. They would then arise directly from the collapse of large gas clouds. This is the so-called ‘heavy seed scenario’. Another idea is that the first black holes swallowed matter much faster than thought, allowing them to grow much faster.
The most exotic – and speculative – proposal is that they are descended from so-called primordial black holes. These could have been created a fraction of a second after the Big Bang, when the universe was expanding rapidly.
According to Maiolino, the scenario of the greedy, matter-gobbling black hole seems the most likely. The bright light emitted by the disk of the black hole in GN-z11 indicates that it is a voracious one, which consumes the gas and dust in its environment more enthusiastically than current supermassive black holes. But the researchers are not sure yet.
Maiolino: ‘We and other teams are actively searching for even further, and therefore older, black holes. Information about their masses and voracity will hopefully allow us to distinguish between the different scenarios.’