It doesn't. Only a tiny fraction is actually ejected into space. The rest is gravitationally bound and collapses quickly back down.
As long as the star is burning the heat/energy generation exerts an outward force on the star which stops it from collapsing. When this ends (after the hydrogen runs out it begins to fuse helium, which produces much more heat causing the sun to expand, but is ultimately the last stop before fusion cannot continue - at which point nothing is 'pushing' the star out, so it collapses back into itself. If it is sufficiently massive, the collapse is so strong that even matter cannot stop it, so the actual atoms collapse into themselves leaving what we call a singularity - a point in space of essentially infinite gravity where all the laws of physics are completely out to lunch.
Thank you. I now understood how the black hole is formed.. What about the time duration of the supernova stage?
Thanks. I'll see the article on wikipedia later. No, I don't want more details.... Thank you Bikerman.
Correct me if I'm wrong (I was never good at Stellar Evolution), but doesn't a Red Super Giant undergo a Supernova to leave a Neutron Star and only under certain conditions (i.e. the Volkhoff limit or something) will the Neutron Star collapse into a Black Hole?
pretty much. The Red Giant part is only a description applied to a 'normal' main sequence star that has used up the hydrogen in the core.