GW250114 reveals signatures of post-merger black-hole horizon

Key Points:

• Recent advances in black hole spectroscopy focus on probing direct waves in ringdowns and testing fundamental properties such as Hawking’s area law and the Kerr nature of black holes using gravitational wave data from events like GW250114.
• The first Event Horizon Telescope results revealed the shadow of the supermassive black hole in M87, providing direct observational evidence complementing gravitational wave studies of black holes.
• Methodological developments include rational filters, quasinormal-mode filters, and multimode analyses to extract and identify ringdown modes, including overtones and nonlinear effects, from gravitational wave signals.
• Studies on nonlinearities, quadratic quasinormal modes, and late-time tails in black hole ringdowns demonstrate complex mode couplings and emergent phenomena, enhancing the understanding of black hole dynamics beyond linear perturbation theory.
• Collaborative efforts by LIGO, Virgo, and KAGRA continue to update gravitational-wave catalogs and refine data analysis techniques, improving the precision of tests of general relativity and black hole physics through gravitational wave observations.