Bautista, Yilber FabianYilber FabianBautistaHuang, Yu-TinYu-TinHuangKim, Jung-WookJung-WookKim2025-08-072025-08-072025-02-14https://scholars.lib.ntu.edu.tw/handle/123456789/731127In this paper, we define absorptive Compton amplitudes, which capture the absorption factor for waves of spin-weight-s scattering in black hole perturbation theory. At the leading order, in the GMω expansion, such amplitudes are purely imaginary and expressible as contact terms. Equipped with these amplitudes we compute the mass change in black hole scattering events via the Kosower-Maybee-O'Connell formalism, where the rest mass of a Schwarzschild/Kerr black hole is modified due to absorption of gravitational, electromagnetic, or scalar fields sourced by other compact object. We reproduced the power loss previously computed in the post-Newtonian expansion. The results presented here hold for similar mass ratios and generic spin orientation, while keeping the Kerr spin parameter to lie in the physical region χ≤1.journal article10.1103/PhysRevD.111.044043