Primordial black hole formation with full numerical relativity

Abstract

We study the formation of black holes from subhorizon and superhorizon perturbations in a matter dominated universe with 3+1D numerical relativity simulations. We find that there are two primary mechanisms of formation depending on the initial perturbation's mass and geometry — via direct collapse of the initial overdensity and via post-collapse accretion of the ambient dark matter. In particular, for the latter case, the initial perturbation does not have to satisfy the hoop conjecture for a black hole to form. In both cases, the duration of the formation the process is around a Hubble time, and the initial mass of the black hole is M BH ∼ 10-2 H -1 M Pl 2. Post formation, we find that the PBH undergoes rapid mass growth beyond the self-similar limit M BH α H -1, at least initially. We argue that this implies that most of the final mass of the PBH is accreted from its ambient surroundings post formation.

New mechanism for primordial black hole formation during reheating

“…Simulations of scalar field collapse are still to provide accurate conditions for PBH formation during the reheating stage (see however Ref. [36]). Our novel mechanism provides explicit conditions for PBH formation beyond the simplistic dust-like scenario.…”

PBH formation from spherically symmetric hydrodynamical perturbations: a review

“…Some works have considered this scenario with scalar fields type [198][199][200][201][202][203], specially taking into account the oscillatory behavior of scalar field during the reheating. Recently in [204] were performed simulations in full GR using scalar fields to modulate the perturbation and the expanding dust background of the Universe, showing that the PBH mass grows beyond the self-similar limit M PBH ∝ H −1 , at least initially. The dust collapse has also been studied in a more oriented perfect fluid scenario [205].…”

Snowmass2021 Cosmic Frontier White Paper:Primordial Black Hole Dark Matter

“…Primordial black holes (PBHs) could form at early times from the direct gravitational collapse of large density perturbations that originated during inflation. The same fluctuations that lay down the seeds of galaxies, if boosted on small scales, can lead to some small areas having a Schwarzschild mass within the horizon, which spontaneously collapse to form black holes [7][8][9][10][11] (as recently confirmed with numerical relativity [12]). Non-detections of PBH are thus also constraints on the small-scale power spectrum, as shown in Figure 3.…”