Causal mechanism of gravity (Was... )

Painius wrote, reposting one of the VS'ers:

Got evidence for push gravity, Paine?

Ask him to explain the mechanism that crushes a massive star down to a
BH. Ask what mechanism POWERS that stellar collapse that drives the
fusion that rebounds as a supernova. Ask what mechansim powers the far
more energetic, *sustained* process of a quasar, making those super/and
hypernovae look like little one-shot "pops" by comparison.