Electromagnetic Signatures of Mirror Stars

Abstract: Mirror Stars are a generic prediction of dissipative dark matter models, including minimal atomic dark matter and twin baryons in the Mirror Twin Higgs. Mirror Stars can capture regular matter from the interstellar medium through extremely suppressed kinetic mixing interactions between the regular and the dark photon. This accumulated "nugget" will draw heat from the mirror star core and emit highly characteristic X-ray and optical signals. In this work, we devise a general parameterization of mirror star nugget properties that is independent of the unknown details of mirror star stellar physics, and use the Cloudy spectral synthesis code to obtain realistic and comprehensive predictions for the thermal emissions from optically thin mirror star nuggets. We find that mirror star nuggets populate an extremely well-defined and narrow region of the HR diagram that only partially overlaps with the white dwarf population. Our detailed spectral predictions, which we make publicly available, allow us to demonstrate that optically thin nuggets can be clearly distinguished from white dwarf stars by their continuum spectrum shape, and from planetary nebulae and other optically thin standard sources by their highly exotic emission line ratios. Our work will enable realistic mirror star telescope searches, which may reveal the detailed nature of dark matter.