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

Anais Pauchet, Devesh Nandal

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 \(ρ_χσ_{\mathrm{SD}}\simeq2\times10^{-28}\,\mathrm{GeV\,cm^{-1}}\), 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.

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 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 to and three initial rotation rates between zero and . As soon as the capture product reaches , 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 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 , rather than the required without WIMPs. For a star with , the surface hydrogen fraction drops to , helium rises to , and primary 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.

Paper Structure

This paper contains 21 sections, 13 equations, 8 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Methods
  3. Capture Rate
  4. Annihilation Rate
  5. Normalization and Equilibrium
  6. Results
  7. Non-rotating models
  8. Hertzsprung-Russell evolution
  9. Main–sequence lifetimes
  10. Internal structure
  11. Rotating models
  12. Moderate rotation (20 % $v_{\rm crit}$) vs. no rotation
  13. Faster rotation: 40–60 % $v_{\rm crit}$
  14. Main-sequence lifetimes
  15. Chemical abundance evolution in DM–supported Pop III stars
  16. ...and 6 more sections

Figures (8)

  • Figure 1: Hertzsprung–Russell diagram from this work (solid lines) and T08 (dashed lines) for a static 20 M$_\odot$ Pop III star surrounded by different WIMPs densities shown with specific colors.
  • Figure 2: Central temperature as a function of WIMP density for a 20 M$_\odot$ Pop III star without rotation left, and with a rotation 20% of $v_{\rm crit}$right. Curves corresponding to different evolutionary stages (defined by the central hydrogen abundance) are plotted with spline interpolation; the dashed curves are taken from T08.
  • Figure 3: Similar plot as \ref{['fig:HRD_norot']} with an initial rotation velocity of 20 % $v_{\rm crit}$. The grey curve represents the non-rotating tracks.
  • Figure 4: HRD of a Pop III star of 20 M$_\odot$, from the ZAMS to the end of the MS, for a WIMPs density of $\rho_\chi \sigma_\text{SD} = 6.3\cdot 10^{-29}$$\text{GeV}\cdot\text{cm}^{-1}$, for an initial veloicity at 20% and 40% of the critical velocity of the star
  • Figure 5: Surface $\Omega/\Omega_{\rm crit}$ versus time for 20 (bottom), 40 (middle), and 60% (top) $v_{\rm crit}$ models at several WIMPs density with a color scheme similar to \ref{['fig:HRD_rot-all']}.
  • ...and 3 more figures