Black holes in thermal bath live shorter: implications for primordial black holes

TL;DR

This paper demonstrates that black holes in a thermal bath emit a modified Hawking radiation spectrum, leading to faster decay rates of primordial black holes, which impacts their cosmological evolution and potential observational signatures.

Contribution

It introduces a new correction to Hawking radiation spectrum for black holes in thermal baths, affecting their decay rates and primordial black hole lifetimes.

Findings

Black holes in thermal baths emit a reshaped Hawking spectrum.

Decay rates of primordial black holes are significantly increased.

Light primordial black holes decay faster, influencing early universe cosmology.

Abstract

Hawking radiation from a non-extremal black hole is known to be approximately Planckian. The thermal spectrum receives multiple corrections including greybody factors and due to kinematical restrictions on the infrared and ultraviolet frequencies. We show that another significant correction to the spectrum arises if the black hole is assumed to live in a thermal bath and the emitted radiation gets thermalised at the bath temperature. This modification reshapes the thermal spectrum, and leads to appreciable deviation from standard results including modification in the decay rate of black holes. We argue that this altered decay rate has significance for cosmology and, in a realistic setting, show that it alters the life time of primordial black holes (PBHs) in the early universe. In particular, the very light PBHs formed right after the end of inflation decay faster which may have interesting phenomenological implications.