# Anatomy of a thermal black hole mimicker

## TL;DR

This paper develops a thermal gas model of 2-2-holes in quadratic gravity, exploring their thermodynamics and geometry as potential black hole mimickers, with implications for observational tests of strong gravity.

## Contribution

It introduces a tractable thermal gas model of 2-2-holes, analyzing their thermodynamic and geometric properties, and distinguishes behaviors at different size limits.

## Key findings

- Large 2-2-holes have minimal exterior deviations and squeezed interiors.
- Anomalous thermodynamic features emerge from the gas model.
- Small 2-2-holes behave like normal thermodynamic systems.

## Abstract

We are entering a new era to test the strong gravity regime around astrophysical black holes. The possibility that they are actually horizonless ultracompact objects and then free from the information loss paradox can be examined more closely with observational data. In this paper, we systematically develop a thermal gas model of the 2-2-hole in quadratic gravity, as one step further to look for more tractable models of black hole mimickers. Concrete predictions for departures from black holes are made all the way down to the high curvature interior. The simple form of matter further enables an explicit study of the relation between geometry and thermodynamics. Within this unified framework, we identify notably different behaviors at two limits. On one side is the astrophysically large 2-2-hole, as characterized by a minuscule deviation outside the would-be horizon and a highly squeezed interior along the radial direction. Anomalous features of black hole thermodynamics emerge from the ordinary gas. On the other side is the minimal 2-2-hole with an isotropic and shrinking interior, which behaves more like a normal thermodynamic system. This brings a new perspective to the related theoretical questions as well as phenomenological implications.