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

Abstract

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 \(20\,M_\odot\) Population III model with the \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 \(3\times10^{10}\,\mathrm{GeV\,cm^{-3}}\) and three initial rotation rates between zero and \(0.4\,v/v_{\mathrm{crit}}\). As soon as the capture product reaches \(\rho_\chi\sigma_{\mathrm{SD}}\simeq2\times10^{-28}\,\mathrm{GeV\,cm^{-1}}\), 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 \(0.4\,v/v_{\mathrm{crit}}\) 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 \(0.2\,v/v_{\mathrm{crit}}\), rather than the \(\gtrsim0.5\,v/v_{\mathrm{crit}}\) required without WIMPs. For a star with \(0.4\,v/v_{\mathrm{crit}}\), the surface hydrogen fraction drops to \(X\!\sim\!0.27\), helium rises to \(Y\!\sim\!0.73\), 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.