Approaching the surface of an Exotic Compact Object

TL;DR

This paper explores the chaotic behavior of spacetime metrics near the surface of Exotic Compact Objects (ECOs), drawing parallels with cosmological billiards and connecting to string theory fuzzball interiors.

Contribution

It demonstrates that vacuum Einstein equations imply chaotic oscillations near ECO surfaces, linking these to cosmological models and string theory fuzzballs.

Findings

Chaotic oscillations occur near ECO surfaces.

Potential walls in the billiard model can turn into cliffs, causing runaway behavior.

Collapse of compact directions relates to string theory fuzzball interiors.

Abstract

Many approaches to quantum gravity require replacing the traditional black hole geometry with an Exotic Compact Object (ECO), which has a large but not infinite redshift at its surface. We argue that near the ECO surface, the vacuum Einstein equations imply a metric that is chaotic, with increasingly large oscillations as we approach the surface. This behavior is analogous to the `cosmic billiards' found in the BKL analysis of cosmology near the big bang. For the ECO, some of the potential walls of this billiards change sign to become `cliffs', resulting in a runaway behavior where some compact directions squeeze to zero size. In string theory such squeezing yields a natural continuation to the interior geometry of fuzzballs, where compact directions collapse to create monopoles.