Boson dark matter halos with a dominant noncondensed component

TL;DR

This paper models galaxy halos using bosonic dark matter particles mostly in a noncondensed state, predicting density profiles consistent with observations and suggesting a particle mass around 86 eV.

Contribution

It introduces a novel model combining noncondensed bosons and Bose stars to explain galaxy halo structures, fitting observational data with specific particle mass constraints.

Findings

Model fits galaxy rotation curves well

Particle mass around 86 eV is favored

Bose stars help avoid density cusps

Abstract

We consider galaxy halos formed by dark matter bosons with mass in the range of about a few tens or hundreds eV. A major part of the particles is in a noncondensed state and described under the Thomas-Fermi approach. Derived equations are solved numerically to find the halo density profile. The noncondensed state is supported in the entire halo except compact gravitationally bounded Bose-Einstein condensates. Although the size of these compact objects, also known as Bose stars, depends on interactions between the particles, its upper limit is only about 100 astronomical units. The Bose stars collect the condensed bosons providing a density cusp avoidance in the halo as well as a natural mechanism to prevent overproduction of small halos. Clusters of the Bose stars can also contribute to the halo density profile. The model is analyzed by confronting its predictions with observations of galaxy rotation curves. We employ 22 low surface brightness galaxies and obtain that the model is consistent with the observational data when the particle mass is in the range above about 50 eV and the best fit corresponds to the mass $m=86$ eV. This mass is appropriate for relic dark matter bosons, which decouple just after QCD phase transition.