The DarkStars code: a publicly available dark stellar evolution package

We announce the public release of the ‘dark’ stellar evolution code DarkStars. The code simultaneously solves the equations of WIMP capture and annihilation in a star with those of stellar evolution assuming approximate hydrostatic equilibrium. DarkStars includes the most extensive WIMP microphysics of any dark evolution code to date. The code employs detailed treatments of the capture process from a range of WIMP velocity distributions, as well as composite WIMP distribution and conductive energy transport schemes based on the WIMP mean-free path in the star. We give a brief description of the input physics and practical usage of the code, as well as examples of its application to dark stars at the Galactic centre.

💡 Research Summary

The paper announces the public release of DarkStars, a stellar evolution code that simultaneously solves the equations governing weakly interacting massive particle (WIMP) capture, annihilation, and energy transport together with the standard equations of stellar structure under the assumption of approximate hydrostatic equilibrium. DarkStars distinguishes itself by incorporating the most comprehensive set of WIMP microphysics available in any dark‑stellar evolution package to date. It accepts a wide range of WIMP velocity distributions—including Maxwellian, anisotropic, and stream components—and computes capture rates that depend on the star’s gravitational potential, temperature profile, and the chosen WIMP–nucleon or WIMP–electron cross sections. Once captured, WIMPs are distributed inside the star according to a composite scheme that switches between diffusion‑type transport and free‑streaming behavior based on the local mean free path relative to the stellar radius. This approach yields a realistic description of conductive energy transport and allows the code to self‑consistently calculate the heating from WIMP annihilation and its feedback on nuclear burning, radiative transfer, and convection.

The software architecture is modular, interfacing cleanly with existing nuclear reaction networks, opacity tables, and convection prescriptions, much like the widely used MESA framework. Users specify input parameters such as WIMP mass, spin‑independent and spin‑dependent cross sections, dark‑matter density and velocity dispersion at the location of interest, and the initial stellar mass and composition. DarkStars then iterates to find a steady‑state balance between capture and annihilation, ensuring numerical stability over gigayear‑scale evolutions.

To demonstrate its capabilities, the authors present simulations of “dark stars” located near the Galactic centre, where dark‑matter densities can reach ∼10⁹ GeV cm⁻³ and velocity dispersions are low. In these environments, capture rates become extremely high, and the annihilation luminosity can dominate over conventional nuclear fusion. The resulting stellar models are inflated, have low surface temperatures (a few thousand kelvin), and exhibit suppressed nuclear burning—features that match theoretical predictions for dark‑matter‑powered stars.

Overall, DarkStars provides the community with a powerful, open‑source tool for exploring the interplay between particle dark matter and stellar physics. Its detailed treatment of capture, annihilation, and conductive transport opens new avenues for probing dark‑matter properties through astrophysical observations, studying the evolution of stars in high‑density dark‑matter environments, and investigating the role of WIMPs in early‑universe star formation and the dynamics of the Galactic centre.