Stability and pulsation of the first dark stars

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 the order of M-circle dot and may grow to a few million solar masses; in this work we investigate the properties of early DSs with masses up to similar to 1000 M-circle dot, 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 similar to 1000 M-circle dot 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 similar to 200 M-circle dot 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.

Automated summary

This study investigates the properties and pulsation modes of dark stars, showing that acoustic modes in smaller dark stars are excited by mechanisms in layers with partially ionized hydrogen or helium. It also reveals that mass-loss rates potentially induced by pulsations are negligible compared to accretion rates.