EVOLUTION OF PRIMORDIAL STARS POWERED BY DARK MATTER ANNIHILATION UP TO THE MAIN-SEQUENCE STAGE

Primordial stars formed in the early universe are thought to be hosted by compact dark matter (DM) halos. If DM consists of weakly interacting massive particles (WIMPs), such stars may be powered by DM annihilation during the early phases of their evolution. We study the pre-main-sequence evolution of the primordial star using a detailed stellar evolution code under the assumption that the annihilation of adiabatically contracted WIMP DM within the star provides sufficient energy to sustain the stellar equilibrium. We follow the evolution of accreting stars using several gas mass accretion rates derived from cosmological simulations. We show that the stellar mass becomes very large, up to 900–1000 M☉ when the star reaches the main-sequence phase for a reasonable set of model parameters such as DM particle mass and the annihilation cross section. During the dark star phase, the star expands by over a thousand solar radii, while the surface temperature remains below 104 K. The energy generated by nuclear reactions is not dominant during this phase. We also study models with different gas mass accretion rates and the DM particle masses. All our models for different DM particle masses pass the dark star phase. The final mass of the dark stars is essentially unchanged for DM mass of mχ ⩽ 10 GeV. Gravitational collapse of the massive dark stars will leave massive black holes with mass as large as 1000 M☉ in the early universe.

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