# A core-halo pattern of entropy creation in gravitational collapse

## TL;DR

This paper introduces a kinetic theory model revealing a core-halo entropy pattern during gravitational collapse, showing entropy destruction in the core and creation in the halo, which may help identify structure formation.

## Contribution

It presents a novel kinetic theory approach demonstrating core-halo entropy patterns in gravitational collapse without prior assumptions, aiding structure formation analysis.

## Key findings

- Entropy destruction in the core and creation in the halo during collapse
- Core-halo pattern emerges without prior assumptions
- Proposes a new scheme for identifying structure formation

## Abstract

This paper presents a kinetic theory model of gravitational collapse due to a small perturbation. Solving the relevant equations yields a pattern of entropy destruction in a spherical core around the perturbation, and entropy creation in a surrounding halo. This indicates collisional "de-relaxation" in the core, and collisional relaxation in the halo. Core-halo patterns are ubiquitous in the astrophysics of gravitational collapse, and are found here without any of the prior assumptions of such a pattern usually made in analytical models. Motivated by this analysis, the paper outlines a possible scheme for identifying structure formation in a set of observations or a simulation. This scheme involves a choice of coarse-graining scale appropriate to the structure under consideration, and might aid exploration of hierarchical structure formation, supplementing the usual density-based methods for highlighting astrophysical and cosmological structure at various scales.