Binary Black Hole Mergers: Structures & Vocabulary

A binary black hole merger proceeds through inspiral, merger, and ringdown. Gravitational-wave observations encode the component masses and spins, orbital geometry, luminosity distance, and tests of strong-field general relativity even when no electromagnetic light is produced.

Gravitational radiation removes energy and angular momentum, raising orbital frequency as separation decreases. The final collision forms a distorted common horizon, and the remnant radiates remaining asymmetry as gravitational waves until only mass and spin dominate its exterior state.

Detected chirp waveforms match general-relativistic templates across inspiral, merger, and ringdown. Independent detectors observe consistent signals, and inferred final masses are smaller than the initial mass sum by an amount corresponding to energy radiated in gravitational waves.

The inspiral is characterized by component masses, spins, eccentricity, and orientation. Near merger, a common horizon forms; the final remnant settles toward a Kerr state through damped ringdown modes.