Heavy dark matter in rapidly evolving massive stars

TL;DR

This work analyzes heavy DM capture in Population III massive stars using time-dependent stellar profiles from MESA and an enhanced multi-scattering framework that includes three-target scattering in metal-rich cores. By employing the Eddington inversion for the DM velocity distribution, the study shows that capture rates are significantly affected by stellar evolution, composition, and halo environment, with MB distributions overestimating rates. For annihilating DM, capture and annihilation rapidly reach equilibrium and exert minimal impact on stellar evolution, while non-annihilating DM can accumulate to self-gravitate and potentially form a central black hole that destroys the star in parts of parameter space. The results highlight the critical role of accurate stellar modeling and halo context in deriving robust constraints on heavy DM from primordial stars and in assessing possible astrophysical DM consequences.

Abstract

We study the impact of heavy dark matter (DM) captured in massive stars via scattering(s) with the star constituents. We focus on the first stars and use stellar evolution simulations to track down how DM capture evolves over time from the zero-age main sequence to the late metal-rich stages of stellar evolution. During the early hydrogen-helium-dominated phase, the capture process is well described by scattering with two targets. As a star evolves, metal production leads to the formation of a dense core surrounded by a lighter envelope. The core significantly enhances the capture of ultra-heavy DM; in this case, three distinct nuclear species are required to accurately describe multiple-scattering capture. We use the Eddington inversion method to obtain a realistic DM velocity distribution, better suited when the star is near the center of a halo, than the widely used Maxwell-Boltzmann distribution. We find that heavy DM would be able to thermalize and achieve capture-annihilation equilibrium within a massive star's lifetime for regions of the parameter space not excluded by direct detection. For non-annihilating DM, because of the high amount of targets available for capture and despite massive stars being short-lived, it would even be possible for DM to achieve self-gravitation and collapse to a black hole, which eventually could swallow the star from within before the expected end of the star's life, for non-excluded regions of the parameter space. Our results highlight the dependence of DM capture on the stellar evolutionary stage, composition, and halo location, demonstrating that accurate modeling of massive stars is essential for constraining heavy DM with primordial stellar populations.

Figures (11)

• Figure 1: Evolution of the matter content of $20\, M_\odot$, $100\, M_\odot$ and $1000\, M_\odot$ Pop. III stars from the zero age main sequence (ZAMS) until He depletion from the core, obtained using MESA with parameters taken from Ref. Windhorst:2018wft.
• Figure 2: Left: Escape velocity profiles at the ZAMS and He depletion stages of the Pop. III stars presented in Fig. \ref{['fig:n_profiles']}. Right: Temperature profiles for the same stages of the same Pop. III stars.
• Figure 3: Possible trajectories the DM can follow in a Pop. III star in the main sequence (left) and red giant stage (right). The two possible paths and optical depths associated with the DM-nucleus scattering are shown. Note that in the star's late stage, the star has acquired a metal-rich core, which depending on the star mass is composed mainly of either ${}^{16}$O and ${}^{12}$C, or ${}^{16}$O and ${}^{20}$Ne, and developed a metal-free atmosphere.
• Figure 4: Dark matter velocity distribution function in the star's frame, obtained using the Eddington inversion method Eddington:1916 for a $10^5\, M_\odot$ halo at redshift $z=10$ with a DM density profile in Eq. \ref{['eq:NFW_profile']} (solid magenta line), and for a star at a radial distance $r_\star=5{\rm \, pc}$ from the center of the halo. For comparison, we also show a Maxwell-Boltzmann velocity distribution using $v_\star\,=\,v_d\,=\,v_{\rm circ}(r_\star=5{\rm \, pc})$ (dashed light blue line).
• Figure 5: DM capture rate in the zero age main sequence (ZAMS) stage of a Pop. III star with $M_\star=1000 \, M_\odot$ at 5 pc from the halo center. The solid magenta line represents the total capture rate calculated using Eq. \ref{['eq:total_capture']} and the DM velocity distribution obtained using the Eddington inversion method (see Fig. \ref{['Fig:Vel_dist']}). The dashed light-blue line represents the total capture obtained using the same procedure but with a Maxwell-Boltzmann velocity distribution, Eq. \ref{['eq:fMB']}. Finally, the dashed orange line shows the result obtained using the formalism in Ref. Ilie:2021iyh.