Gravitational Wave Inspiral

Binary black hole/neutron star merger — GW chirp signal from post-Newtonian approximation

Binary System

Chirp mass M_c:
Frequency f:
Separation a:
Strain h:
Time to merge:
h(t) ~ M_c^(5/3) f^(2/3)
ḟ = (96/5)π^(8/3)(GM_c/c³)^(5/3) f^(11/3)
The gravitational wave frequency chirps upward as the orbit decays. M_c = (m₁m₂)^(3/5)/(m₁+m₂)^(1/5) is the chirp mass — the primary observable.

GW150914 (LIGO 2015): first detection, M_c≈28.3 M☉, merge at ~150 Hz.