The Evolution of Pop III.1 Protostars Powered by Dark Matter Annihilation. I. Fiducial model and first results

The existence of billion-solar-mass quasars at redshifts $z\gtrsim 7$ poses a formidable challenge to theories of black hole formation, requiring pathways for the rapid growth of massive seeds. Population III.1 stars, forming in pristine, dense dark matter (DM) minihalos, are compelling progenitors. This study presents a suite of stellar evolution models for accreting Pop III.1 protostars, calculated with the $\text{textsc}GENEC$ code. We systematically explore a wide parameter space, spanning ambient WIMP densities of ${\rho }_{\chi }\sim {10}^{12}-{10}^{16}\mathrm{G}\mathrm{e}\mathrm{V}\mathrm{c}{\mathrm{m}}^{-3}$ and gas accretion rates of ${10}^{-3}-{10}^{-1}{M}_{\odot }\mathrm{y}{\mathrm{r}}^{-1}$, to quantify the effects of DM annihilation. A central finding is that for a protostar to grow to supermassive scales ($\gtrsim {10}^5{M}_{\odot }$), the ambient DM density in the immediate vicinity of the star must exceed a critical threshold of ${\rho }_{\chi }\gtrsim 5\times {10}^{14}{\text{GeV cm}}^{-3}$. The energy injected by WIMP annihilation inflates the protostar, lowering its surface temperature, which suppresses the ionizing feedback that would otherwise halt accretion and significantly delays the onset of hydrogen fusion. This heating also governs the star’s final fate: in dense halos (${\rho }_{\chi }\gtrsim {10}^{15}\mathrm{G}\mathrm{e}\mathrm{V}\mathrm{c}{\mathrm{m}}^{-3}$), stars remain stable against general relativistic instability beyond ${10}^6{M}_{\odot }$, whereas at lower densities (${\rho }_{\chi }\lesssim {10}^{13}\mathrm{G}\mathrm{e}\mathrm{V}\mathrm{c}{\mathrm{m}}^{-3}$), they collapse at masses of $\sim 5\times {10}^5{M}_{\odot }$. Once the DM fuel is exhausted and core burning commences, the protostar contracts and its ionising photon output can reach very high levels $\sim {10}^{53}{s}^{-1}$. 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.