Jumbo shrimp!
The point is that the gravitation is the source of energy for the compression, which is the source of energy for the heat/pressure, which is the source of energy trying to make the gas expand..... you can't end up with more energy in the form of heat/pressure to "overcome" the force of gravity, because gravity is the ONLY source of energy in the process (contracting gas cloud) being described. For it to be otherwise would consitute a violation of conservation of energy.
Any cloud of material undergoing gravitational contraction eventually reaches an equilibrium point at which the internal pressure is exactly balanced against the gravitational forces trying to contract the cloud. The more massive the cloud, the higher the density is before equilibrium is reached. If the cloud is massive enough, the internal conditions eventually reach sufficient pressure and temperature to initiate nuclear fusion reactions, which in turn, provide a new source of heat (and radiation pressure), which stops the cloud (now star) from collapsing further.
And what happens when the star uses up the material able to fuse in the fusion regions in the stars interior? The fusion process starts to shut down, and energy and radiation pressure drop, so the star starts to contract again, further raising internal pressure and temperature, until eventually it is hot enough and dense enough for heavier nuclei to start to fuse, and a new round of fusion reactions, much more powerful than the hydrogen fusion process that preceeded it, and thus the higher energy and radiation pressure causes the star to expand again but to a much larger diameter than previously. This is the so-called "red giant" phase that occurs at the end of a star's life cycle.
This cycle repeats with ever heavier nuclei fusing and ever higher rates at ever higher pressures and temperatures, and the star get bigger and bigger..... until the material in the core has been fused into iron nuclei, at which point the reaction process stops, the now enormous star once again undergoes gravitational collapse as there is no longer any process left by which to generate enough energy in the core to stop it.
If the star is less than about 1.4 solar masses, it eventually finds an equilibrium state in which the pressure of the gases exactly balance the gravitational forces, but no nuclear reactions are possible, and the star simply cools off as it radiates it energy away, fading away as a dwarf star.
If the mass is more than 1.4 solar masses, but less than about 4 solar masses, the internal gravitational forces increase faster than the gas pressure can resist it, and the star cannot find an equilibrium state while the matter is still a gas. This results in the formation of a neutron star, where finally equilibrium is once again restored, but at a vastly smaller diamater than the original star.
And if the star is greater than about 4 solar masses, not even the neutron state can provide enough resistance to find an equilibrium in which the gravitational force is balanced, and the star collapses until the outer, hydrogen rich regions are compressed ALL AT ONCE to the fusion flash point, resulting in a supernova explosion of the outer regions of the star. If what remains is less than 4 solar masses, a neutron star may result, if larger than 4 solar masses, the remaining matter undergoes final, complete gravitational collapse for which there is no known force powerful enough to resist the increasing gravitational forces, and a black hole is the result.
Jumbo shrimp!
Thank you LS. Want to clarify something. It appears you are stating that the outer matter, at the final stage of a +4 solar mass star in collapse, experiences very violent gravitational pull from the core, however, is still far enough away from that core to heat and then explode. Simply a matter of rapid compression and enough distance. Is this correct?
Sorry, this isn't correct. I should have read this more carefully, but I was busy using Google image search to find a picture of a shrimp.
The fusion that takes place in a supernova is negligible. What powers a supernova is the gravitational collapse of the core. Think about it: as the core falls inwards, a gigantically large amount of gravitational potential energy is released. This is true whether the core collapses to a black hole or a neutron star. The energy released is typically larger than the total energy derived from fusion over the life of the star(!) That energy has to go someplace, and as the outer layers of the star are optically thick, they absorb it, and are blown out into space. They even absorb a surprisingly large fraction of the neutrino emissions.