A white dwarf has a greater mass than either a red dwarf or a brown dwarf. Yet a white dwarf has a smaller radius than either a red dwarf or a brown dwarf. Explain why, in terms of the types of pressure that keep the different kind of dwarfs from collapsing under their own gravity.

In the world of stellar physics, electron degeneracy pressure is a truly exotic and powerful concept. Imagine a mash-up of quantum mechanics and the dense matter found in white dwarfs, and you've got a snapshot of what electron degeneracy pressure is all about. It comes from the Pauli Exclusion Principle, which is like an exclusive club rule for electrons: no two electrons can have the same set of quantum numbers, meaning they can't share the same space.

As a result, when a star like our Sun has consumed its nuclear fuel, it cannot hold out against gravity by the usual mechanism of heat generation - cue electron degeneracy pressure. This force arises because the electrons in the white dwarf's core are squeezed so close together that they resist further compression - not because they're hot and bothered, but because they're following quantum laws. This is why a white dwarf is super dense and has a small radius, despite having a greater mass than red or brown dwarfs.

If electron degeneracy pressure is the dense quantum phenomenon, then thermal pressure is its more familiar, festive cousin. It's the jostling you feel in a crowded room - where every particle is buzzing with energy, bouncing off each other. In stars like red dwarfs or brown dwarfs, this is the main event. Thermal pressure is the result of heat; it's basically particle rave inside a star causing it to puff up like a marshmallow over a campfire.

This stellar party is what keeps smaller and cooler red and brown dwarfs from succumbing to a gravitational squeeze. They rely on the heat produced by nuclear reactions, which make particles move faster, push harder, and expand the star's volume. That's why these stars can have a larger radius, despite their smaller mass compared to white dwarfs - they're being held up by the thermal energy produced by nuclear fuel, which white dwarfs lack.

Our final act in this cosmic drama is gravitational collapse. This force plays the relentless villain in the story of stellar life. A star's existence is a delicate balance, a tug of war between inward pull and outward push. Throughout its life, a star fights gravity by burning nuclear fuel, creating pressure - like a balloon with a constant influx of air.

However, when the star's nuclear fuel starts running dry, gravity begins to win. The star starts to shrink under its own weight. If you've got something like a massive white dwarf, electron degeneracy pressure might hold up the fight against gravity. But when those forces aren't enough, it could collapse further, possibly becoming a neutron star or a black hole. Gravitational collapse is the ultimate endpoint of stellar evolution, the moment when the celestial scales tip in favor of gravity, leading to one of the most mysterious and extreme objects in the universe.