Faster and closer
As the two objects orbit, they lose energy to gravitational waves, so they spiral closer together and orbit faster. The waves oscillate at twice the orbital frequency, so the pitch and the loudness rise together: a chirp.
Explore · Sound
Hear a chirp
Two black holes or neutron stars spiral together, faster and faster, until they merge. Pick their masses and listen to the gravitational-wave signal they’d make.
Real events
On laptop or phone speakers? Low notes can be hard to hear: shift the pitch up. Shifting changes only the pitch, not the timing.
- Total mass
- Chirp mass
- Mass ratio
- Time above 20 Hz
- Cycles above 20 Hz
- Rings down at
- Final black hole
What you’re hearing
Why it chirps
Heavier is lower and shorter
How fast the pitch sweeps upward is set by one combination of the two masses, the chirp mass. Light neutron stars spend minutes sweeping up through a detector’s band, completing thousands of cycles. Heavy black holes are in and out in a fraction of a second.
The ringdown
When two black holes merge, the new black hole settles down by “ringing”, like a struck bell, at a frequency set by its mass and spin. Heavier black holes ring lower. Two neutron stars collide before that happens; what follows depends on nuclear physics.
About this model
This is an illustrative model, not a research-grade waveform. The inspiral uses the leading-order (quadrupole) frequency evolution, with amplitude growing as the frequency to the power 2/3. For black holes, the frequency then rises smoothly to the ringdown frequency of the final black hole, whose mass and spin come from fits to numerical-relativity simulations (Berti et al. 2007; Rezzolla et al. 2008), with the ringdown frequency and damping time from Berti, Cardoso & Will (2006).
It leaves out the spins of the two objects, orbital eccentricity, higher harmonics and, for neutron stars, tides and everything after the stars touch (taken here as two 12-km stars meeting). Objects up to 2.5 solar masses are labelled neutron stars. Masses are in the source frame, and the loudness is normalised, so distance isn’t included.
Signals start at 20 Hz, roughly where today’s detectors start to be sensitive, except when that would take longer than ten seconds; light systems then start partway through.