[mirimir]

Thanks. I see now that it's merging binary neutron stars that create the huge gamma spikes.[0]

[0] https://www.astro.cf.ac.uk/research/gravity/tutorial/?page=4...

Edit: That tutorial also explains that black holes are very simple objects, so the chirps and ringdowns are likewise very simple. So black hole masses can be calculated very precisely. Also, amazingly:

> Just as optical radiation and radio waves, the luminosity of gravitational radiation falls off in inverse proportion to the square of the distance from the source. This makes binary black hole inspirals standard sirens: if we know what the masses of the two black holes are then we can infer the distance to the source by measuring its apparent luminosity. We can precisely measure the masses because the rate at which the frequency and amplitude of an inspiral increases depends only on the masses.