Primordial black holes (PBHs) are a hypothetical type of black hole that formed soon after the Big Bang. These are plausible dark matter candidates and are also good candidates for being the seeds of the supermassive black holes at the center of massive galaxies, as well as of intermediate-mass black holes.
There are different scenarios for the formation of PBHs. One can classify them into three classes: (i) collapse of horizon-size overdensities; (ii) subhorizon assembly of massive objects (such as heavy particles, supersymmetric Q-balls, or oscillons) (iii) subhorizon assembly of massive particles in the presence of radiative cooling due to Yukawa or other long-range forces.
Now, Flores and Kusenko discussed the spins of primordial black holes produced in all these scenarios.
“The evolution of PBH spins to the present day depends on the merger history and the details of accretion. To start, we first considered the spin evolution of BH distributions accessible by present-day gravitational wave experiments, i.e., for masses ≳ 10 M.”
At first, they suggested that, black holes that form from collapse of horizon-size density perturbations have negligible spins.
Next, the black holes that formed from merger of particles or scalar field solitons in the absence of radiative cooling can have a range of spins, from small to large.
Finally, in the presence of radiative cooling (which is essential in some formation scenarios), the angular momentum is removed from a collapsing halo faster than the energy, leading to slowly rotating black holes.
“The prospects for measuring the black hole spin distribution with gravitational waves will open a new window on the early universe cosmology if some of the black holes are confirmed to have primordial origin.”— concluded authors of the study
Reference: Marcos M. Flores, Alexander Kusenko, “Spins of primordial black holes formed in different cosmological scenarios”, Arxiv, pp. 1-6, 2021. https://arxiv.org/abs/2106.03237
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