PBH formation from spherically symmetric hydrodynamical perturbations: a review

TL;DR

This review summarizes recent theoretical, numerical, and analytical developments in understanding primordial black hole formation from spherically symmetric curvature fluctuations in the early universe.

Contribution

It compiles and discusses current results, formalism, and numerical methods for PBH formation, highlighting the latest threshold and mass estimates.

Findings

Different thresholds for PBH formation depending on curvature fluctuation sets

Numerical simulations provide detailed insights into PBH mass distribution

Analytical estimates are contrasted with numerical results for formation conditions

Abstract

Primordial black holes, which could have been formed in the very early Universe due to the collapse of large curvature fluctuations, are nowadays one of the most attractive and fascinating research areas in cosmology for their possible theoretical and observational implications. This review article presents the current results and developments on the conditions for primordial black hole formation from the collapse of curvature fluctuations in spherical symmetry on a Friedman-Lemaitre-Robertson-Walker background and its numerical simulation. We review the appropriate formalism for the conditions of primordial black hole formation, and we detail a numerical implementation. We then focus on different results regarding the threshold and the black hole mass using different sets of curvature fluctuations. Finally, we present the current state of analytical estimations for the primordial black hole formation threshold, contrasted with numerical simulations.