[hinoki]

Is both. They cause gravitational waves, which is how the system gets rid of energy, which allows the orbits to decay, causing the collision (and more waves).

[MattPalmer1086]

To be clear, the fact that the collision causes more waves does not seem to be relevant here.

It is the loss of energy due to gravitational wave emission that causes the collision. Ambient gravitational waves from other sources do not seem to play a part?

[raverbashing]

Maybe if you're close enough but probably not in the majority of cases

Gravitational waves are really weak

[ano-ther]

Thank you