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What kind of pressure supports a white dwarf?
electron degeneracy pressure
What is fermi pressure?
This is a guess, but I suspect the person means the electron degeneracy pressure.
What prevents a white dwarf from completely collapsing upon itself?
Further collapse of a white dwarf is prevented by electron degeneracy pressure.
How is degeneracy pressure related to white dwarfs and neutron stars?
White dwarfs are prevented from collapsing further by electron degeneracy pressure. If the mass of a stellar remnant exceeds the Chandrasekhar limit, about 1.4 solar masses, gravity will overcome this pressure and form a much smaller and denser neutron star. Further collapse in a neutron star is prevented by neutron degeneracy pressure up until the Tolman-Oppenheimer-Volkoff limit of about 3 solar masses, at which point gravity causes a complete collapse, forming a black hole.
Why do white dwarfs not continue to contract as they cool?
White dwarfs do not contract because the electron degeneracy pressure is stronger than gravity for stars with masses like white dwarfs. It holds them apart.
Is white drawf bigger than a nertron star?
Simply, neutron star is a big nuclear - of 10km radius and solar mass (mass density about  1017- 1018 kg/m3). The material in a white dwarf is supported by electron degeneracy pressure. The physics of degeneracy yields a maximum mass for a non-rotating white dwarf, the Chandrasekhar limit-approximately 1.4 solar masses-beyond which it cannot be supported by electron degeneracy pressure. The density of white dwarf is - 109 kg/m3. So its radius is much bigger 10km, but the mass can be less, as well as bigger of solar mass.
How do neutron stars form?
When a medium-size star runs out of fuel (hydrogen to fuse into helium), it will collapse on itself. It has a large enough mass that it can push past the resistance from electron degeneracy pressure. When it collapses more, it will get stopped by neutron degeneracy pressure. It will settle at a star that is about 20 kilometers in diameter. The star fuses protons with electrons, and these form neutrons to make a kind of "neutron soup".
Why don't the outer layers of a white dwarf continue to be pulled inward?
Because the gravity is not enough to overcome electron degeneracy pressure. White dwarf star material is so dense that in order for it to get any denser the electrons in the atoms making it up would have to be squeezed together. For a star the mass of the Sun, this density occurs when the star becomes about the size of Earth. Stars that are more than about one and a half times the mass of the Sun do have enough gravitational pull to overcome electron degeneracy pressure, and they shrink even more, winding up a dozen miles or so across. At this density (which is comparable to the density of an atomic nucleus), they are neutron stars and are kept from collapsing any further by neutron degeneracy pressure. Stars that are even larger have enough mass to overcome even that and wind up as a black hole; once you've passed the neutron degeneracy pressure, there's really nothing left to keep you from collapsing all the way into a singularity.
What keeps white dwarf from collapsing under its own weight?
A white dwarf star, as well as any other stable variety of star,is held together by the pressure popularly known as "gravity".In the opposite direction, white dwarf stars are kept from collapsing completely by degeneracy pressure. Specifically, for white dwarf stars, it's electron degeneracy pressure, which arises from the fact that electrons are fermions and cannot all occupy the same energy state. For higher mass stars, the force of gravity is able to overcome this and push all the electrons into the ground state, and the star is supported by a different kind of degeneracy ... neutron degeneracy, which is the same thing but with neutrons ... and you get a neutron star. At even higher masses, even that isn't sufficient and the star collapses all the way into a black hole.
Is ower sun big enough to make a black hole?
No. The only mechanism by which black holes are known to form is the gravitational collapse of a star with a mass at least 20 times that of our Sun. All objects require some outward force to balance gravity. In main sequence stars, the outward flow of energy from the nuclear reactions in the core creates an outward pressure to balance gravity. Once the fuel is exhausted and the core collapses, there are two more forms of pressure which can halt collapse. First, electron degeneracy pressure, which can be thought of as a repulsion between electrons. Electron degeneracy pressure can support a body of up to approximately 1.4 times the mass of the Sun, and stars that end their life in this state are known as white dwarves. Second, neutron degeneracy pressure; repulsion between neutrons. We are less certain about the extent to which neutron degeneracy pressure can support a body against gravitational collapse, but we understand the limit to be somewhere around 2.5 times the mass of the Sun. Stars that end in this state become neutron stars. An object experiencing gravitational collapse which has a mass greater than can be supported by neutron degeneracy pressure will collapse into a black hole. Note, that it is not the entire star that collapses, merely the core. The outer envelope of the star is ejected as a planetary nebula in the case of lower mass stars, and in a supernova in the case of higher mass stars.
What happens when the gravity of a massive star overcomes neutron degeneracy pressure?
The core contracts and becomes a black hole.
What prevents neutron stars from contracting to a smaller size?
Neutron degeneracy pressure, in which the neutrons themselves prevents further collapse.
