Dark-Matter-Powered Population III Evolution: Lifetimes, Rotation, and Quasi-Homogeneity in massive Stars

Population III stars supplied the first light and metals in the Universe, setting the pace of re-ionisation and early chemical enrichment. In dense haloes their evolution can be strongly influenced by the energy released when WIMPs annihilate inside the stellar core. We follow the evolution of a $20M_{\odot }$ Population III model with the $\text{textsc}genec$ code, adding a full treatment of spin dependent WIMP capture and annihilation. Tracks are calculated for six halo densities from ${10}^8$ to $3\times {10}^{10}\mathrm{G}\mathrm{e}\mathrm{V}\mathrm{c}{\mathrm{m}}^{-3}$ and three initial rotation rates between zero and $0.4v\mathrm{/}{v}_{\mathrm{c}\mathrm{r}\mathrm{i}\mathrm{t}}$. As soon as the capture product reaches ${\rho }_{\chi }{\sigma }_{\mathrm{S}\mathrm{D}}\simeq 2\times {10}^{-28}\mathrm{G}\mathrm{e}\mathrm{V}\mathrm{c}{\mathrm{m}}^{-1}$, the dark-matter luminosity rivals hydrogen fusion, stretching the main-sequence lifetime from about ten million years to more than a gigayear. The extra time allows meridional circulation to smooth out differential rotation; a star that begins at $0.4v\mathrm{/}{v}_{\mathrm{c}\mathrm{r}\mathrm{i}\mathrm{t}}$ finishes core hydrogen burning with near solid-body rotation and a helium core almost twice as massive as in the dark-matter-free case. Because the nuclear timescale is longer, chemically homogeneous evolution now sets in at only $0.2v\mathrm{/}{v}_{\mathrm{c}\mathrm{r}\mathrm{i}\mathrm{t}}$, rather than the $\gtrsim 0.5v\mathrm{/}{v}_{\mathrm{c}\mathrm{r}\mathrm{i}\mathrm{t}}$ required without WIMPs. For a star with $0.4v\mathrm{/}{v}_{\mathrm{c}\mathrm{r}\mathrm{i}\mathrm{t}}$, the surface hydrogen fraction drops to $X\text{\hspace{0.17em}⁣}\sim \text{\hspace{0.17em}⁣}0.27$, helium rises to $Y\text{\hspace{0.17em}⁣}\sim \text{\hspace{0.17em}⁣}0.73$, and primary ${}^{14}\mathrm{N}$ increases by four orders of magnitude at He exhaustion. Moderate rotation combined with plausible dark-matter densities can therefore drive primordial massive stars towards long-lived, quasi-homogeneous evolution with distinctive chemical and spectral signatures.