Interaction between bosonic dark matter and stars

TL;DR

This paper analyzes how bosonic dark matter condensates interact with stars, showing they can form stable, oscillating composite stars that do not necessarily lead to collapse, challenging previous assumptions about dark matter accretion.

Contribution

It provides a detailed analysis of bosonic dark matter interactions with stars, including stability criteria and the formation of oscillating composite stars, extending prior simplified models.

Findings

Bosonic condensates can form stable, oscillating configurations within stars.

Dark matter cores grow but are halted near the Chandrasekhar limit.

Dark matter accretion does not inevitably cause star collapse or black hole formation.

Abstract

We provide a detailed analysis of how bosonic dark matter "condensates" interact with compact stars, extending significantly the results of a recent Letter. We focus on bosonic fields with mass $m_B$, such as axions, axion-like candidates and hidden photons. Self-gravitating bosonic fields generically form "breathing" configurations, where both the spacetime geometry and the field oscillate, and can interact and cluster at the center of stars. We construct stellar configurations formed by a perfect fluid and a bosonic condensate, and which may describe the late stages of dark-matter accretion onto stars, in dark matter-rich environments. These composite stars oscillate at a frequency which is a multiple of $f=2.5\times 10^{14}\,\left(m_{B}c^2/eV\right)\,{\rm Hz}$. Using perturbative analysis and Numerical Relativity techniques, we show that these stars are generically stable, and we provide criteria for instability. Our results also indicate that the growth of the dark matter core is halted close to the Chandrasekhar limit. We thus dispel a myth concerning dark matter accretion by stars: dark mater accretion does not necessarily lead to the destruction of the star, nor to collapse to a black hole. Finally, we argue that stars with long-lived bosonic cores may also develop in other theories with effective mass couplings, such as (massless) scalar-tensor theories.