Supermassive gravitinos and giant primordial black holes

TL;DR

This paper proposes that stable supermassive gravitinos could form primordial black holes early in the universe, which then grow to large sizes, potentially explaining the existence of massive black holes observed today.

Contribution

It introduces a novel mechanism where supermassive gravitinos form bound states that seed primordial black holes, a process supported by gravitational and electric forces in the early universe.

Findings

Bound states of gravitinos can collapse into mini-black holes.

Black holes can grow by accretion and survive evaporation.

This mechanism explains the formation of large black holes in the early universe.

Abstract

We argue that the stable (color singlet) supermassive gravitinos proposed in our previous work can serve as seeds for giant primordial black holes. These seeds are hypothesized to start out as tightly bound states of fractionally charged gravitinos in the radiation dominated era, whose formation is supported by the universally attractive combination of gravitational and electric forces between the gravitinos and anti-gravitinos (reflecting their `almost BPS-like' nature). When lumps of such bound states coalesce and undergo gravitational collapse, the resulting mini-black holes can escape Hawking evaporation if the radiation temperature exceeds the Hawking temperature. Subsequently the black holes evolve according to an exact solution of Einstein's equations, to emerge as macroscopic black holes in the transition to the matter dominated era, with masses on the order of the solar mass or larger. The presence of these seeds at such an early time provides ample time for further accretion of matter and radiation, and would imply the existence of black holes of almost any size in the universe, up to the observed maximum.