The gravitational Vavilov-Cherenkov effect

TL;DR

This paper proposes a novel gravitational analog of the Vavilov-Cherenkov effect, where an uncharged black hole moving faster than light in a medium emits radiation due to a collective medium effect, with potential astrophysical implications.

Contribution

It introduces a new gravitational Cherenkov-like effect for uncharged black holes, combining gravitational and electromagnetic radiation mechanisms, expanding understanding of black hole-medium interactions.

Findings

Black holes can emit radiation when moving superluminally in a medium.

The radiation involves both gravitational and electromagnetic components.

Potential detection methods for primordial black holes are discussed.

Abstract

In this essay we show that an uncharged black-hole moving superluminally in a transparent dielectric medium violates Hawking's area theorem. The violation is overcome through the emission of radiation. Since modes cannot emerge from the black hole itself, this radiation must originate from a collective effect in the medium, in complete analogy with the Vavilov-Cherenkov effect. However, because the black-hole is uncharged, the emission mechanism must be different. We discuss the physical origin of the effect and obtain a Newtonian estimative. Then we obtain the appropriate equations in the relativistic case and show that the field which is radiated away is a combination of gravitational and electromagnetic degrees of freedom. Possible astrophysical relevance for the detection of primordial black-holes and binary systems is discussed.