An international team of astronomers has discovered the oldest black hole, which already existed at the cosmic dawn, when the universe was barely 400 million years old, according to a study published Wednesday.
This detection sets back that of a massive black hole by “around 200 million years,” notes Jan Scholtz, astrophysicist at the Kavli Institute of Cosmology at the British University of Cambridge, to AFP.
It “will fuel a new generation of theoretical models” to explain such a phenomenon in the young universe, more than 13 billion years ago, added this co-author of the study published in the journal Nature.
We must imagine an object with a mass estimated at 1.6 million times that of our Sun. Invisible, like all black holes, it absorbs the surrounding matter by emitting a phenomenal quantity of light at its periphery.
It is this light which made it possible to detect the galaxy at the heart of which it is lurking, called GN-z11 when its discovery was announced in 2016 using the Hubble space telescope.
GN-z11 was then the oldest, and therefore most distant, galaxy observed by Hubble. Until the arrival in 2022 of the James Webb space telescope, which enabled the detection of the GN-z11 black hole.
This detection is added to others made with the James Webb, which reveal a young universe housing objects much brighter than expected.
The black hole detected by the international team led by Cambridge is dated to 430 million years after the Big Bang. It is the time of the cosmic dawn, when at the end of the so-called “dark” ages the first stars and galaxies are born.
Several scenarios
The problem, for a black hole of this size, is to understand how it could have grown so quickly. It normally takes times of several hundred million or several billion years for those discovered later.
Its characteristics “suggest a faster and earlier growth than that of other black holes known at very early times,” explains Stéphane Charlot, astrophysicist at the Paris Institute of Astrophysics and co-author of the study, to AFP.
And therefore “mechanisms for the formation of black holes in the young universe which could be different from those we know in the closer universe”, he adds.
If we stick to classic scenarios, “the universe is then too young to host such a massive black hole, so we have to consider other ways for its appearance”, observes Professor Roberto Maiolino, astrophysicist at Cambridge and first author of the study, cited in a press release.
Theorists imagine that such an object was born “large”, from the explosion of a supermassive star at the end of its life, or from the rapid concentration of a cloud of dense gas, without going through the phase of star formation.
Once well born, the black hole of GN-z11 would then have gorged itself on the surrounding gas to grow rapidly. And all the more easily since “the observations seem to indicate a high density of this gas”, according to Mr. Charlot.
The study of Nature “does not rule out any of these scenarios” according to Jan Scholtz, who is banking on the extraordinary observation capabilities of the James Webb telescope to shed light on the phenomenon.
“We can expect to detect others when we have a greater number of in-depth observations of larger portions of the sky,” hopes the astrophysicist.