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 halos, their evolution can be strongly influenced by the energy released when weakly interacting massive particles (WIMPs) are annihilated inside the stellar core. We followed the evolution of a 20 M⊙ Population III model with the GENEC code, adding a full treatment of spin-dependent WIMP capture and annihilation. Tracks were calculated for six halo densities from 108 to 3 × 1010 GeV cm−3 and three initial rotation rates between 0 and 0.4 v/vcrit. As soon as the capture product reaches ρχ σSD ≃ 2 × 10−28 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/vcrit 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/vcrit, rather than the ≳ 0.5 v/vcrit required without WIMPs. For a star with 0.4 v/vcrit, the surface hydrogen fraction drops to X ∼ 0.27, helium rises to Y ∼ 0.73, and primary 14N increases by four orders of magnitude at He exhaustion. The star leaves the zero age main sequence cooler, at Teff ≈ 50 kK, and should display the strong N III and He II lines typical of a nitrogen-rich Wolf-Rayet analogue. 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. Our tracks offer quantitative inputs for models of re-ionisation, for stellar archaeology, and for future attempts to constrain the microphysics of WIMPs through high-redshift observations.