Michael Baker and colleagues discussed the new mechanism of formation of primordial black holes (PBH’s) during a first-order phase transition in the early Universe. Their study recently appeared in Arxiv.
Primordial black holes are a hypothetical type of black hole that formed soon after the Big Bang. There are several possible formation mechanisms of primordial black holes (PBH’s): the most widely studied is collapse of density perturbations generated during inflation, while the collapse of topological defects, the dynamics of scalar condensates, or collisions of bubble walls during a first-order phase transition are viable alternatives.
Now, Michael Baker and colleagues, proposed a new mechanism of PBH production during a first-order cosmological phase transition.
“While previous papers on this topic have only considered the energy density stored in the bubble wall, we focused on a population of particles that interact with the bubble wall and showed that during a first-order phase transition, the energy density of the reflected particles can reach sufficient densities to trigger collapse into PBHs.”— wrote M. Baker and his collaborators
They considered a particle species that interact/collides with the bubble wall. The mass of these particles may increase significantly during phase transitions due to either confinement or a Higgs mechanism. High-momentum particles can pass through the bubble wall into the true vacuum and gain a large mass, while low-momentum χ particles are reflected due to energy conservation (as shown in fig 1 below). The build-up of reflected particles (in front of the walls) creates a density perturbation which may lead to PBH formation.
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They track this process quantitatively by solving a Boltzmann equation, and demonstrated that the mass and density of the PBHs depend on the temperature at which the phase transition occurs and the probability that a black hole will form in a given volume.
Reference: Michael J. Baker, Moritz Breitbach, Joachim Kopp, Lukas Mittnacht, “Primordial Black Holes from First-Order Cosmological Phase Transitions”, Arxiv, pp. 1-7, 2021. https://arxiv.org/abs/2105.07481
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