Excitation of Ringdown Direct Waves

Abstract

It has recently been argued that the merger phase of gravitational waves from binary black hole coalescences contains not only quasinormal modes but also a newly identified component, the so-called “direct wave”. As the “last scream” of two merging black holes before they are silenced by the remnant, this component exhibits a characteristic oscillation and decay pattern controlled by two fundamental properties of the final horizon: its rotation frequency and surface gravity. In this talk, I will present a general physical picture of the direct wave: what it is, how it arises, and how it can be extracted from numerical-relativity simulations and from the loudest observed event, GW250114. I will further discuss how this component can serve as a new probe of horizon dynamics.