The evolution of protostars powered by dark matter annihilation. I. Fiducial model and first results

The existence of billion-solar-mass quasars at redshifts z 7 poses a formidable challenge to theories of black hole formation, requiring pathways for the rapid growth of massive seeds. One such pathway arises from primordial stars powered by dark matter (DM) self-annihilation rather than conventional fusion, which could form massive black hole seeds in ordinary cosmological mini-haloes. Here we present a suite of stellar evolution models for DM-powered protostars, computed with the GENEC code. We explored a wide parameter space, spanning ambient WIMP densities of ρ χ about 10 12--10 16, GeV,cm-3 and gas accretion rates of 10-3--10-1,M, yr-1, to quantify the effects of DM annihilation. A central finding is that for a protostar to grow to supermassive scales (10 5, M), the ambient DM density in the vicinity of the star must exceed a critical threshold of ρ χ 5 times 10 14, GeV cm-3. The energy injected by WIMP annihilation inflates the protostar, lowering its surface temperature, which suppresses the ionising feedback that would otherwise halt accretion and delays the onset of hydrogen fusion. In dense halos (ρ χ 10 15, GeV,cm-3), stars remain stable against general relativistic instability beyond 10 6, M, whereas at lower densities (ρ χ 10 13, GeV,cm-3), they collapse at masses of about 5 times 10 5, M. Once the DM fuel is exhausted and core burning commences, the protostar contracts and its ionising photon output can reach high levels about 10 53: s-1. These distinct evolutionary phases offer clear observational signatures for the JWST, providing a robust, physically grounded pathway for forming heavy black hole seeds in the early Universe.