"Extremely dense matter is like a crowded parking lot. All of the low energy "parking spaces" are taken, so electrons are forced into higher energy states, not because they are hot, but because there is nowhere else to go. This creates a "degenerate" electron pressure (degenerate refers, not to the moral character of the electrons, but to the fact that all the low energy states are occupied). This pressure is what prevents white dwarf stars from collapsing under their own weight."