Neutron Stars are the most dense category of stars that form when a star collapses in on itself. These stars have 1.4 solar masses (1.4 times larger than our sun) and have a radius of 6.2 miles. The reason they have the name "Neutron Stars" is also because it is believed that they are comprised of mostly neutrons.

Neutron Stars also lose the ability to generate heat because of how tightly packed the particles are against each other. Despite this surface cooling, it may still be very hot due through further collisions with other stars or an accretion (a gravitationally bound disk of particles).