One of the common questions I get is (averaged across many versions) “Why don’t all stars become black holes – don’t they all have gravity? And why don’t they start as Black Holes – didn’t they start with all that mass that made them become black holes?
Balancing stars against gravitational collapse is actually a process that is much more simple than many people think. When a star forms, the pressure and density in the center causes nuclear reactions to occur. These reactions release energy, partially in the form of photons, and the photons exert a pressure on the outer layers of the star. The light pressure pushes outward with the same force that the gravity presses inward. As long as nuclear reactions are occurring in the star’s center, the star doesn’t collapse. When stars die, their nuclear reactions stop and without the pressure from the light they collapse. If a star is similar to the Sun, it becomes a white dwarf, and the force of the electrons repelling one another supports the star. If a star is more massive, the electrons and protons in the stars atoms get crushed together and become neutrons, and the star is supported by the neutrons pushing against each other. If the star is even more massive, there is nothing left to support the star against gravitational collapse and it becomes a black hole.
So, for every force, their is an opposing force, and in black holes, well, inside the BH, we have no idea what is happening, but whatever it is, it kicks in after the material has collapsed small enough that we can get close enough to the center of mass that bad things can happen. Spaghetification anyone?