Astrophysicists from Johns Hopkins University (USA) tested whether the mysterious "little red dots" in images from the James Webb Space Telescope could conceal primordial black holes - hypothetical objects that could have formed before the first stars appeared. The work was published in the journal Physical Review Letters.
Ordinary black holes form through the gravitational collapse of stars. Primordial ones, as co-author Valerio De Luca explained, are linked to the physics of the early Universe, when it was expanding rapidly, and their formation mechanism is entirely different. The idea of such objects was proposed by Stephen Hawking, but there is still no direct evidence of their existence.
In search of an answer, the scientists turned their attention to the red dots - compact regions in the images that may be incandescent disks of gas, dust and energy around black holes. The question is which of them are linked to primordial black holes, if these exist at all.
As a proof of concept, the researchers took the object QSO1. It existed just 700 million years after the Big Bang and, unlike other red dots, consists almost entirely of hydrogen and helium - the first elements of the Universe - and lacks heavier elements.
The scientists constructed three scenarios and determined under what conditions a primordial black hole could have grown to the size of QSO1 and acquired a surrounding disk. The most likely option was the one in which a small primordial black hole attracted and absorbed surrounding gas and energy, gradually increasing in size. At the same time, cosmological observations impose constraints: there cannot be too many primordial black holes, including in a single cluster.
The authors emphasize that this is modeling, not proof. To confirm the existence of primordial black holes, it is necessary to find an object either too light for an ordinary black hole or so ancient that it is older than the first stars. In the future, the researchers plan to assess how many of the roughly 100 known red dots could be primordial black holes.