Black Hole Spectroscopy
When black holes merge, the final black hole "rings" like a struck bell, emitting gravitational waves at specific frequencies. On January 14, 2025, LIGO detected GW250114 — the clearest gravitational wave ever recorded (SNR 77, vs. previous record 42). For the first time, physicists could confidently extract two distinct "tones" from the ringdown: the fundamental mode and its first overtone. Each tone independently measures the black hole's mass and spin. If general relativity is correct, they should match. They did — the most stringent single-event test of Einstein's theory to date.
LIGO/Virgo/KAGRA Collaboration, Physical Review Letters, November 2025
Click: cycle view | 1-3: select view | Space: pause | I: info