Neutron stars are the collapsed left overs of giant stars, like white dwarfs and black holes. They are usually more than twice of the sun's mass. Around this mass, stars collapse when they are out of fuel rather than blow up and form planetary nebula, they collapse until the pressure becomes much stronger than its gravity to blow up, which is called supernova. The leftover after a supernova is either neutron stars or black holes. The difference of conditions to form black holes and neutron stars is their mass. Interestingly, the minimum mass to become black hole is about 1.4 times the mass of the sun, which is similar to the average mass of neutron stars, 1.44 times the mass of the sun. As this was figured out, scientists theorized another force to resist gravity and prevent neutron stars from collapsing into a black holes, other than inner thermal pressure. With the development of quantum mechanics, the degenerate pressure was discovered.

Degeneracy pressure comes from the Pauli's Exclusion Principle and Heisenberg's uncertainty principle which explains quantum dynamics. Pauli’s Exclusion Principle states that “Fermions cannot have identical values.” This means that protons, neutrons, and electrons cannot take the same positions, or energies. And Heisenberg's uncertainty principle states that “Position and velocity of a particle can not be measured at the same time.” This means as the position of a particle becomes more precise, the uncertainty of velocity of a particle increases. As particles do not take the same position and their velocity increases, resisting pressure, temperature increases when the particles have less space to occupy, causing them to reduce the uncertainty of position of each particle and increasing uncertainty of velocity of each particle according to two principles.

Even though the degenerate pressure can prevent neutron stars from collapsing into a black hole, it has a certain limit to be endlessly strong. The speed of light, which no things with mass can ever reach, enables black holes to form even after disturbances of quantum phenomena. As super massive stars collapse, the degenerate pressure increases the same as normal, but the degenerate pressure, which is caused from velocity of particles, will not increase until the light speed, and the pressure will also not increase at that point. And when the super massive stars are massive enough to produce stronger gravitational force than this limit-reached resistant pressure, that star will finally collapse into a black hole, which now even the light cannot escape, and seems to break the laws of physics.

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