Effect of inhomogeneity on primordial black hole formation in the matter dominated era

Abstract

We investigate the effect of inhomogeneity on primordial black hole formation in the matter dominated era. In the gravitational collapse of an inhomogeneous density distribution, a black hole forms if apparent horizon prevents information of the central region of the configuration from leaking. Since information cannot propagate faster than the speed of light, we identify the threshold of the black hole formation by considering the finite speed for propagation of information. We show that the production probability β inhom (σ) of primordial black holes, where σ is density fluctuation at horizon entry, is significantly enhanced from that derived in previous work in which the speed of propagation was effectively regarded as infinite. For σ ≪ 1, we obtain β inhom ≃ 3.70σ 3/2 , which is larger by about an order of magnitude than the probability derived in earlier work by assuming instantaneous propagation of information.

The First Three Seconds: a Review of Possible Expansion Histories of the Early Universe

“…We also refer to Ref. [56] for another effect, which allows to simply multiply the expression for β by an additional power ∝ σ 3/2 induced by the initial inhomogeneity of the Universe. However, a complete analysis of generation of finite spin and suppression of β with an initial inhomogeneity has not been fully done.…”

“…In particular, they can have a significant impact on our expectations for the DM relic abundance, since nonstandard eras can change the expansion rate of the Universe [38,39], lead to entropy injections that may dilute the DM relic abundance [40], or provide a nonthermal production mechanism for DM [41,42]. Furthermore, a period of nonstandard cosmology may also impact small scale structure formation, potentially enhancing or impeding the formation of dense ultracompact DM microhalos [43,44,45,46,47], axion miniclusters [48,49], and primordial black holes (PBH)s [50,51,52,53,54,55,56]. The survival of nongravitational relics (including, for example and in addition to DM, matterantimatter asymmetry [57,58,59,60,61], primordial magnetic fields [62,63,64,65,66], or effective number of relativistic species [67,68]) will depend on the details of the expansion history and post-inflationary thermalization of radiation.…”

PBH Formation from Spherically Symmetric Hydrodynamical Perturbations: A Review

“…The PBH formation has also been considered in the context of the Lemaître-Tolman-Bondi (LTB) model [209,210]. In [211], the effect of inhomogeneity on PBH formation in the matter-dominated era and its consequences on the PBH production were studied. On the other hand, in [200,212], the non-spherical effects and spins for PBH formation in the case of a dust-dominated Universe were studied, showing this could have a significant effect.…”

Neutrino and Positron Constraints on Spinning Primordial Black Hole Dark Matter

“…Given this increased scrutiny of PBHs (which started after the direct detection of gravitational waves [30,31] and the subsequent proposal that these BHs are primordial in nature [32][33][34][35]), it is obvious to ask if we have explored all the properties of BHs in our searches for PBHs. Typically, it has been assumed that PBHs have low spins [36][37][38], however, there exist viable cosmological scenarios where PBHs are born with a high spin [39][40][41][42][43][44][45][46]. Angular momentum is a fundamental property of BHs and it is crucial to explore its implications [47][48][49][50].…”