Numerical simulation of type II primordial black hole formation

TL;DR

This paper uses numerical simulations to explore the formation and characteristics of type II primordial black holes in a radiation-dominated universe, revealing complex horizon structures and the influence of initial fluctuation profiles on PBH mass.

Contribution

It demonstrates that type II initial fluctuations do not always produce type II PBHs in radiation-dominated conditions and highlights the role of fluctuation profiles in PBH mass outcomes.

Findings

Type II fluctuations do not always lead to type II PBHs in radiation-dominated universe.

PBH mass can increase or decrease with initial amplitude depending on the fluctuation profile.

Characteristic bifurcating trapping horizon structures are observed in certain PBH formations.

Abstract

This study investigates the formation of type II primordial black holes (PBHs) resulting from extremely large amplitudes of initial fluctuations in a radiation-dominated universe. We find that, for a sufficiently large initial amplitude, the configuration of trapping horizons shows characteristic structure due to the existence of bifurcating trapping horizons. We call this type of configuration of the trapping horizons type II-B PBH, while the structure without a bifurcating trapping horizon type II-A PBH. In Ref. [1], in the dust-dominated universe, the type B PBH can be realized by the type II initial fluctuation, which is characterized by a non-monotonic areal radius as a function of the radial coordinate (throat structure) in contrast with the standard case, type A PBH with a monotonic areal radius (type I fluctuation). Our research reveals that a type II fluctuation does not necessarily result in a type B PBH in the radiation-dominated case. We also find that for an initial amplitude well above the threshold value, the resulting PBH mass may either increase or decrease with the initial amplitude, depending on its specific profile rather than its fluctuation type.