Primordial Black Holes

TL;DR

This paper reviews the history, formation mechanisms, constraints, and observational evidence of primordial black holes, highlighting their potential roles in dark matter, gravitational wave sources, and cosmic structure formation.

Contribution

It provides a comprehensive overview of primordial black holes, emphasizing recent shifts towards observational evidence and their significance in cosmology.

Findings

Primordial black holes could account for dark matter.

Evidence suggests PBHs may produce detectable gravitational waves.

PBHs might seed supermassive black holes and early cosmic structures.

Abstract

In this chapter we first describe the early history of primordial black hole (PBH) research. We then discuss their possible formation mechanisms, including critical collapse from inflationary fluctuations and various types of phase transition. We next describe the numerous constraints on the number density of PBHs from various quantum and astrophysical processes. This was the main focus of research until recently but there is currently a shift of emphasis to the search for evidence for PBHs. We end by discussing this evidence, with particular emphasis on their role as dark matter candidates, sources of gravitational waves and seeds for supermassive black holes and early cosmic structures.