Monthly Notices of the Royal Astronomical Society | 2021
Stability and pulsation of the first dark stars
Abstract
The first bright objects to form in the Universe might not have been ordinary fusion-powered stars, but Dark Stars (DSs) powered by the annihilation of dark matter (DM) in the form of Weakly Interacting Massive Particles (WIMPs). If discovered, DSs can provide a unique laboratory to test DM models. DSs are born with a mass of order $M_\\odot$ and may grow to a few million solar masses; in this work we investigate the properties of early DSs with masses up to $\\sim \\! 1000 \\, M_\\odot$, fueled by WIMPS weighing $100$ GeV. We improve the previous implementation of the DM energy source into the stellar evolution code MESA. We show that the growth of DSs is not limited by astrophysical effects: DSs up to $\\sim \\! 1000 \\, M_\\odot$ exhibit no dynamical instabilities; DSs are not subject to mass-loss driven by super-Eddington winds. We test the assumption of previous work that the injected energy per WIMP annihilation is constant throughout the star; relaxing this assumption does not change the properties of the DSs. Furthermore, we study DS pulsations, for the first time investigating non-adiabatic pulsation modes, using the linear pulsation code GYRE. We find that acoustic modes in DSs of masses smaller than $\\sim \\! 200 \\, M_\\odot$ are excited by the $\\kappa-\\gamma$ and $\\gamma$ mechanism in layers where hydrogen or helium is (partially) ionized. Moreover, we show that the mass-loss rates potentially induced by pulsations are negligible compared to the accretion rates.