Dark Stars: Improved Models and First Pulsation Results

TL;DR

This paper models dark stars powered by dark matter annihilation, compares results with previous models, and explores their pulsation properties, suggesting potential observational signatures and cosmological applications.

Contribution

It provides improved stellar models for dark stars, including pulsation analysis, with detailed comparisons to prior work and implications for observability.

Findings

Dark stars are hotter and more luminous than previous models suggested.

Models confirm supermassive dark stars are well approximated by (n=3)-polytropes.

Dark star pulsation modes vary from less than a day to over two years, offering potential observational signatures.

Abstract

We use the stellar evolution code MESA to study dark stars. Dark stars (DSs), which are powered by dark matter (DM) self-annihilation rather than by nuclear fusion, may be the first stars to form in the Universe. We compute stellar models for accreting DSs with masses up to 10^6 M_{sun}. The heating due to DM annihilation is self-consistently included, assuming extended adiabatic contraction of DM within the minihalos in which DSs form. We find remarkably good overall agreement with previous models, which assumed polytropic interiors. There are some differences in the details, with positive implications for observability. We found that, in the mass range of 10^4 -10^5 M_{sun}, our DSs are hotter by a factor of 1.5 than those in Freese et al.(2010), are smaller in radius by a factor of 0.6, denser by a factor of 3 - 4, and more luminous by a factor of 2. Our models also confirm previous results, according to which supermassive DSs are very well approximated by (n=3)-polytropes. We also perform a first study of dark star pulsations. Our DS models have pulsation modes with timescales ranging from less than a day to more than two years in their rest frames, at z ~ 15, depending on DM particle mass and overtone number. Such pulsations may someday be used to identify bright, cool objects uniquely as DSs; if properly calibrated, they might, in principle, also supply novel standard candles for cosmological studies.