Primordial black holes are again on the limelight

TL;DR

This paper establishes strict upper limits on primordial black holes in the universe by analyzing their effects on star populations and identifying observational signatures, thereby constraining their possible abundance and formation mechanisms.

Contribution

It introduces a new method to constrain primordial black hole density using stellar depletion and luminosity signatures, refining previous bounds and implications for black hole formation.

Findings

Strong upper bounds on PBH abundance in the universe.

Identification of a characteristic overluminosity signature before star collapse into PBHs.

Constraints that allow stellar-mass black holes in otherwise forbidden mass ranges.

Abstract

We derive a strong upper bound on the amount of Primordial Black Holes (PBHs) that can still be present in the Universe. Gravitational capture of PBHs by the Milky Way stars during their formation and subsequent accretion would produce a dramatic depletion of disk stars and especially of white dwarfs, unless the average cosmic density and mass of PBHs are severely constrained. Our finding also helps to discriminate among the various production mechanisms of PBHs. Moreover, we show that a star becomes overluminous before its disappearance into a PBH for a time span independent of its mass, thereby providing a characteristic observational signature of the considered scenario. We stress that our result allows for the existence of stellar-mass black holes in a mass range that is forbidden by standard stellar evolution.