Hmmm

The event horizon is defined as the point where the

escape velocity = c

c = [tex]\sqrt{\frac{2GM}{r}}[/tex]

where c is the speed of light, 300 million m/s

G is the gravitational constant, 6.67×10

^{−11} [tex]\frac{m^3}{kg s^2}[/tex]

M is the mass of the black hole.

**r** is the radius... where?

I think

**r** has to be the distance to the event horizon.

So, if the mass below the event horizon is symmetrically distributed, and more or less unchanging, then the event horizon should also be unchanging, independent of density.

Now, if the black hole is formed during a supernova. Then could one have an expanding cloud of debris that would be outside of the event horizon, which could then start to rapidly contract?

Another possibility for the formation of a black hole might be the collision of 2 neutron stars, in which as it forms, part of the stars might be within the event horizon, and part of them might be outside of the event horizon. Or, the same thing might be true with the collision of 2 black holes, or a star with a small black hole.

Of course, I also mentioned symmetrically distributed mass. With astronomical events, that may not always be the case.