Binary merger signal: frequency sweeps up as objects spiral in
Binary orbit (inspiral)
Strain h(t) — the chirp waveform
f = — Hz | h = — | r = — AU
A binary black hole system loses energy to gravitational radiation, causing the orbit to shrink and the frequency to increase — the "chirp." The waveform h(t) ∝ ℳ5/3/d · cos(2φ(t)) grows in amplitude and frequency until merger. The chirp mass ℳ = (m₁m₂)^(3/5)/(m₁+m₂)^(1/5) is the best-determined parameter. GW150914 (LIGO 2015) detected this signature from 36+29 M☉ black holes at 410 Mpc, peaking at ~150 Hz.