At the Highest-Frequency Frontier: Thermal Gravitational Waves from Supernovae

Abstract

Core-collapse supernovae can be powerful sources of high-frequency gravitational waves (GWs) as the extreme temperatures and densities in the core allow a considerable number of gravitons to be produced thermally. We present the first systematic calculation of the thermal GW spectrum of a core-collapse supernova. By evaluating the dominant emission channels---including electron and proton photoproduction ($γe^{-}\to he^{-}$, $γp\to h\,p$) and gravitational bremsstrahlung ($e^{-}p\to e^{-}p\,h$, $e^{-}e^{-}\to e^{-}e^{-}h$)---we find that a core-collapse supernova generates a total thermal GW luminosity of $1.27\times10^{26}$ W, approximately 18 orders of magnitude larger than that of the Sun. The thermal GW spectrum peaks at energies of $\mathcal{O}(0.1\,{\rm GeV})$, extending the predicted spectrum of known GW sources to an unprecedented high-frequency regime. Our results provide a benchmark thermal GW spectrum at the high-frequency frontier.