Probing Heavy Dark Matter in Red Giants

Abstract

Red giants (RGs) provide a promising astrophysical environment for capturing dark matter (DM) via elastic scattering with stellar nuclei. Captured DM particles migrate toward the helium-rich core and accumulate into a compact configuration. As the DM population grows, it can become self-gravitating and undergo gravitational collapse, leading to adiabatic contraction through interactions with the ambient medium. The resulting energy release, through elastic scattering and, where relevant, DM annihilation during collapse, locally heats the stellar core and can trigger helium ignition earlier than that predicted by standard stellar evolution. We analyze the conditions under which DM-induced heating leads to runaway helium burning and identify the critical DM mass required for ignition. Imposing the observational constraint that helium ignition must not occur before the observed luminosity at the tip of the RG branch, we translate these conditions into bounds on DM properties. Remarkably, we find that RGs are sensitive to DM, particularly with masses around $10^{11} \,{\rm GeV}$ and spin-independent scattering cross sections near $10^{-37}\,{\rm cm}^2$, which is comparable to the reach of current terrestrial direct detection experiments. Noteworthy, observations of RG stars provide a unique probe for high-mass and large-cross-section DM, a regime that remains currently inaccessible to direct detection experiments.