Dark Dwarfs: Dark Matter-Powered Sub-Stellar Objects Awaiting Discovery at the Galactic Center

TL;DR

This paper explores how dark matter annihilation influences sub-stellar objects near the galactic center, predicting a new class called dark dwarfs that could be detected via lithium-7 retention.

Contribution

It introduces the concept of dark dwarfs as dark matter-powered objects with a higher minimum mass for hydrogen burning, expanding understanding of sub-stellar objects influenced by dark matter.

Findings

Dark dwarfs form near the galactic center where dark matter density is high.

The minimum mass for stable hydrogen burning is increased due to dark matter effects.

Dark dwarfs retain lithium-7, unlike brown and red dwarfs, enabling potential detection.

Abstract

We investigate the effects of dark matter annihilation on objects with masses close to the sub-stellar limit, finding that the minimum mass for stable hydrogen burning is larger than the $\sim0.075 M_\odot $ value predicted in the Standard Model. Below this limit, cooling brown dwarfs evolve into stable dark matter-powered objects that we name dark dwarfs. The timescale of this transition depends on the ambient dark matter density $\rho_{\rm DM}$ and circular velocity $v_{\rm DM}$ but is independent of the dark matter mass. We predict a population of dark dwarfs close to the galactic center, where the dark matter density is expected to be $\rho_{\rm DM}\gtrsim 10^{3}$ GeV/cm$^3$. At larger galactic radii the dark matter density is too low for these objects to have yet formed within the age of the universe. Dark dwarfs retain their initial lithium-7 in mass ranges where brown/red dwarfs would destroy it, providing a method for detecting them.