neutron star is formed when the core of a star, that was one ginormous, collapse on its own mass thus it loses it's volume exponentially (y=a^x) while the mass of the star decreases linearly (y=mx+c) thus the neutron star has mass of 10 to 29 sun in the radius of 10 km( for scale earth has 6731 km) thus it's density is super high!!!!!!!!!!!!!!!!!!!
hope it helps you! ;)
