Black hole event horizons are cosmologically coupled

TL;DR

The paper demonstrates that black hole horizons cannot remain static in an expanding universe without singularities, implying black holes are inherently coupled to cosmological expansion, affecting theories of black hole growth and dark energy.

Contribution

It introduces the idea that black hole horizons must be coupled to cosmic expansion, challenging the assumption of static horizons in dynamic spacetimes.

Findings

Static, spherically symmetric horizons cannot exist in time-dependent geometries.

Forcing a static horizon leads to a naked null singularity.

Black holes must couple to the universe's expansion, influencing their growth and dark energy understanding.

Abstract

It is shown that an exactly static and spherically symmetric black hole event horizon cannot be embedded in a time-dependent geometry. Forcing it to do so results in a naked null singularity at the would-be horizon. Therefore, since the universe is expanding, black holes must couple to the cosmological expansion, which was suggested as the growth mechanism for supermassive black holes in galaxies, with implications for the dark energy puzzle.