Black holes of various masses may have formed during the first second of the Big Bang and ultimately ended up being the source of dark matter. In a new scenario, these primordial black holes would have given birth to the first stars sooner than previously thought. The James Webb Space Telescope could verify this theory.
An Esa press release echoes an article posted on arXiv and who is a sea serpent of astrophysics and cosmology for about 50 years. The question continues to be debated with multiple oscillations of the pendulum as to their relevance to solving the thorny problems that are the nature of the black matter and the origin of supermassive black holes. It is also hoped that they could be used to demonstrate the existence of Hawking radiation. These are of course the black holes primordial.
Let us go back to the explanations given many times about them in the articles of Futura. These objects are also famous as mini black holes and it is nothing less than Stephen hawking who took special care of it from 1971 based on works published in 1966 through Yakov Zel’dovich and Igor Novikov, two great leaders of Russian astrophysics and relativistic cosmology.
Big Bang fossil black holes
Everything is based on a very simple observation in the reasoning concerning these still theoretical objects. In the context of relativistic cosmological models of the type big Bang, the “initial” density ofUniverse observable had to be very large. If we are to believe the equations trying to describe thestate of matter and the field of gravitation close to the initial cosmological singularity in general relativity classical, the Universe was then very turbulent with chaotic fluctuations of its metric and its density as shown by the work of Charles Misner (model known under the name of Mixmaster universe), as well as those of Belinsky, Khalatnikov and Lifchitz. Very recently, moreover, work on gravitational waves produced at that time showed that the term turbulence could literally be used in its hydrodynamic sense.
Under these hellish conditions, if a fluctuation in density becomes such that a given mass passes under its Schwarzschild radius collapsing under its own gravity, a black hole was to result.
The problem is that we do not know very well how many could have been formed or of which masses, but a large spectrum is possible, depending on the models and physical used to describe this very primitive phase of the observable cosmos. They could theoretically have masses as low as the mass of Planck (Mp= 10-5 g), but also well beyond, for example 1,000 to 105 solar masses, which can therefore serve in the latter case as germs for the training of supermassive black holes.
When the existence of dark matter began to be seriously considered, it was quite naturally explained by bringing in these primordial black holes which are therefore called mini-black holes when their mass and size are much smaller than those. black holes produced by thecollapse from stars. All the black matter, or only a portion, could be made up.
Over the years, multiple observational constraints have been placed on the mass spectrum of primordial black holes, i.e. on the abundances of these objects in a given mass interval in a volume of the observable Universe. Generally, the conclusions reached were quite pessimistic about the existence of these black holes and the fraction of dark matter they could account for.
Speculation was revived with the discovery of gravitational waves produced by mergers black holes in binary systems abnormally massive even if the masses involved are of the order of those of stars. To account for this anomaly, the astrophysicists had suggested that these black holes are in fact primordial black holes, and their detection so fast would imply that they are numerous, to the point of still accounting for dark matter.
Nico Cappelluti (University of Miami), Günther Hasinger (Scientific Director of ESA) and Priyamvada Natarajan (Yale University) have just revived the pendulum with their article accepted for publication in The Astrophysical Journal.
The researchers therefore propose a new model which, according to them, is compatible with the constraints having already excluded many intervals of masses for a given population of primordial black holes and they believe that they have not only killed two birds with one stone. by explaining the origin of supermassive black holes but also dark matter. They also predict an accelerated formation of the first stars and several observational signatures allowing to test, or at least to constrain their scenario.
Primordial black holes born of phase transitions
This takes up the idea recently put forward by other researchers, which involves the formation of primordial black holes in four successive phases. First black holes of planetary masses at the electroweak transition, when the W and Z bosons become massive thanks to the mechanism of Brout-Englert-Higgs, then black holes of the order of the Chandrasehkar mass when the protons and the neutrons are formed by condensation of the quark plasma gluons (another one phase transition), then black holes of the order of 30 solar masses (like those initially discovered with Ligo and whose existence is poorly explained by collapse of stars) when pions are always formed from the quagma and finally black holes of the order of a million solar masses when the electrons and the positrons annihilate each other.
The large population of black holes thus created should produce during collisions gravitational waves that the eLisa detector could highlight in the 2030s. But perhaps the most interesting finding concerns the first stars.
It is the story of a space telescope named James Webb, designed to take over from the mythical Hubble telescope. Its space adventure begins at the Guyanese Space Center in December 2021, where it takes off aboard the Ariane 5 rocket and will be placed in orbit around the Lagrange L2 point of the Earth-Sun system. This telescope contains several instruments including Miri, developed under the responsibility of ESA and national space agencies by a Consortium of European laboratories. © CEA, Cnes, CNRS, Osups
According to the researchers’ calculations, in their scenario, primordial black holes tend to cluster much like stars in a globular cluster and therefore form kinds of mini halos of dark matter bathed in a mixture ofhydrogen and D’helium.
These halos collapse and, carrying with them the distributions of gas surrounding areas, increase their density to the point of initiating fragmentation and collapse into denser regions which will become protostars, processes which would therefore have occurred more quickly than in classical models with dark matter particles.
The first stars will therefore be born sooner than was generally thought in this scenario and, since supermassive black holes will also accrete matter, the telescope James Web should see sources infrared important already during the period called that of dark ages and therefore see significant star formation earlier than expected.
The radiation produced byaccretion of matter on early supermassive black holes should also be detectable, not only in infrared but also in the domain of X-rays.
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