Tidal Love numbers and quasi-normal modes of the Schwarzschild-Hernquist black hole

Abstract

We derive the model of the Schwarzschild black hole immersed into a dark matter halo with a relativistic Hernquist profile, the Schwarzschild-Hernquist black hole, and obtain its tidal Love numbers and quasi-normal modes. We thoroughly compare our odd and even parity perturbation equations with the literature and point out that two distinct choices of matter perturbations lead to distinct spectra. We establish that the quasi-normal modes admit qualitatively distinct scaling laws in terms of dark matter densities for non-relativistic and relativistic halos. We develop a stable numerical scheme for computing tidal Love numbers based on asymptotic series expansions. We further comment upon the existence of matter configurations obeying the dominant energy condition that lead to multiple light rings.