There is a theorized “Eddington Limit” that stars can only grow to a certain mass before the power of their fusion reactions counterbalance gravity and they blow off additional matter instead of absorbing it. It’s approximately a few hundred solar masses.

How does the Eddington Limit relate to black hole formation ? Does it means that accretion is slow until the star's matter has finished fusing ?

Black holes form when there is insufficient force to counter accretion and subsequent compression by gravity. There are a few forces that act as a counter:

- thermally generated pressure as a result of exothermic reactions (like nuclear fusion),

- Coulomb pressure (atomic nuclei opposing each other), or

- quantum-mechanical degeneracy pressure (keeps white and brown dwarfs and neutron stars from collapsing)