// spiral-hymn — gravitational wave sound simulator

Two black holes orbit, lose energy to gravitational waves, and merge. The top-down view shows the outgoing spiral wave in the orbital plane; the sound is that same wave’s strain, sampled by a distant observer in the plane (drag on the view to move the observer). Doppler shifts come from each hole’s motion along the line of sight. Press the sound button to listen.

// from wave to sound

strain h(t) at observer→× 2^transpose × volume→speaker

// frequency track — what each voice does

Dashed grey: the physical gravitational wave frequency. Coloured: what the observer receives after Doppler shift. Frequencies shown are physical, before transposition.

// readouts

Model: leading-order (quadrupole) inspiral, a smooth plunge from the innermost stable orbit, then a ringdown at the quasi-normal-mode frequency from fits for the final black hole. Real signals from numerical relativity differ in detail. Light-travel delay is applied to the top-down view. Observer in the orbital plane sees pure plus polarisation at half the face-on amplitude. Playback speed stretches the event in time but keeps pitch at its physical value.