Bose-Einstein condensate and degenerate Fermi cored dark matter halos

TL;DR

This paper models dark matter halos with highly condensed cores, such as Bose-Einstein condensates or degenerate Fermi cores, using composite polytropes to analyze their structure and observational constraints.

Contribution

It introduces a novel composite polytrope approach to model condensed dark matter cores within halos, applicable to both bosonic and fermionic dark matter.

Findings

Bosonic cores with or without self-interactions are compatible with observations.

Fermionic cores with particle masses between 1-1000 keV are not excluded by current data.

The model can incorporate various equations of state and multi-component systems.

Abstract

There has been considerable interest in the last several years in support of the idea that galaxies and clusters could have highly condensed cores of dark matter (DM) within their central regions. In particular, it has been suggested that dark matter could form Bose--Einstein condensates (BECs) or degenerate Fermi cores. We examine these possibilities under the assumption that the core consists of highly condensed DM (either bosons or fermions) that is embedded in a diffuse envelope (e.g., isothermal sphere). The novelty of our approach is that we invoke composite polytropes to model spherical collisionless structures in a way that is physically intuitive and can be generalized to include other equations of state (EOSs). Our model is very amenable to the analysis of BEC cores (composed of ultra-light bosons) that have been proposed to resolve small-scale CDM anomalies. We show that the analysis can readily be applied to bosons with or without small repulsive self-interactions. With respect to degenerate Fermi cores, we confirm that fermionic particle masses between 1 -- 1000 keV are not excluded by the observations. Finally, we note that this approach can be extended to include a wide range of EOSs in addition to multi-component collisionless systems.