Vasilisa Sergienko | Searcharxiv

arXiv2026

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

The existence of billion-solar-mass quasars at redshifts $z \gtrsim 7$ 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 \textsc{GENEC} code. We explored a wide parameter space, spanning ambient WIMP densities of $ρ_χ\sim 10^{12}\mbox{--}10^{16}\,\mathrm{GeV\,cm^{-3}}$ and gas accretion rates of $10^{-3}\mbox{--}10^{-1}\,M_\odot\,\mathrm{yr^{-1}}$, 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 vicinity of the star must exceed a critical threshold of $ρ_χ \gtrsim 5 \times 10^{14} \, \text{GeV cm}^{-3}$. The energy injected by WIMP annihilation inflates the protostar, lowering its surface temperature, which suppresses the ionising feedback that would otherwise halt accretion and delays the onset of hydrogen fusion. In dense halos ($ρ_χ\gtrsim 10^{15}\,\mathrm{GeV\,cm^{-3}}$), stars remain stable against general relativistic instability beyond $10^6 \, M_{\odot}$, whereas at lower densities ($ρ_χ\lesssim 10^{13}\,\mathrm{GeV\,cm^{-3}}$), 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 high levels $\sim 10^{53}\:{\rm s}^{-1}$. These distinct evolutionary phases offer clear observational signatures for the \textsc{JWST}, providing a robust, physically grounded pathway for forming heavy black hole seeds in the early Universe.

astro-ph.SR↗

arXiv2026

Stellar Yields of Rapidly Rotating Population III Stars for the High Redshift Universe

JWST has revealed rapid nitrogen enrichment in high redshift galaxies, renewing the need for stellar yields that follow metal free stars beyond the main sequence and across their final fates. We present Geneva stellar evolution models of rapidly rotating Pop~III stars with $5 \leq M_{\rm ini}/M_\odot \leq 200$ and $\upsilon_{\rm ini}/\upsilon_{\rm crit}=0.7$, evolved to the end of core O-burning. We calculate gross adopted ejecta masses using fate dependent remnant prescriptions spanning core collapse, pulsational pair instability, and complete pair instability. Our quantitative results focus on hydrostatically produced CNO material, while heavier species are treated as final-model reservoirs. Rotation produces primary CNO material by mixing newly synthesized C and O into H-burning layers, where CNO cycling generates nitrogen. The resulting abundance signature depends strongly on which stellar layers escape. Models leaving compact remnants can reach $\log({\rm N/O})=-0.49$ while remaining poor in Si/S/Ar/Ca-rich material. PISN models eject the largest nitrogen masses, $M_{\rm N}=1.8$--$2.5,M_\odot$, but also release $57$--$65,M_\odot$ of oxygen, lowering $\log({\rm N/O})$ to $-1.44$ to $-1.29$. Thus, high nitrogen yields do not imply high N/O ratios. This trend persists after IMF weighting, as increasingly top-heavy populations add oxygen and deep alpha material faster than they build a nitrogen dominated mixture. Our grid provides a new CNO-focused prompt-enrichment dataset for interpreting nitrogen-rich systems including GN-z11, CEERS-1019, and GS~3073.

astro-ph.GA↗