Gravitationally, neutron stars are the most powerful objects second only to black holes. They are stars that are exactly at the tipping point of turning into a black hole. They are so dense that if we were to take one teaspoon of a Neutron star, it would weigh a billion tons. Where do these city sized (they are just a few kilometers wide) heavyweights come from and how are they formed? Let’s see…
Neutron stars are formed after the death of a star greater than 5 solar masses in a supernova explosion. During a supernova explosion, the atoms in the core are crushed extremely hard. The atoms come very close to each other. The electrons of one atom start repelling the electrons of other atoms. The pressure overpowers the electromagnetic forces between the electrons and the electrons are forced to collapse into the protons in the nucleus. After the collapse, all the protons in the nucleus turn into neutrons.
After all this, when the outer layers of the star bounce off into interstellar space which we see as a supernova explosion, a dense core of neutrons is left behind. this is a neutron star.
Neutron stars are one of the fastest rotating objects in the universe. Due to the law of conservation of angular momentum, if rotating objects get shorter in radius, they start to spin faster. When a star dies, its radius is reduced thousands of times causing the neutron star to spin hundreds of times a second. Fast rotating Neutron stars are known as Pulsars.
Neutron stars are also the biggest magnets in the universe, having a magnetic field that is a billion (10^10) to a quadrillion (10^15) times as powerful as that of the earth. Neutron stars that are magnetically the most powerful are known as magnetars.
Due to immense pressure in a Neutron star, the nucleus of atoms at the center join together to form a long pasta like structure. Scientists call this the Nuclear Pasta (a weird name). The nuclear pasta is so dense that it might just be the hardest thing in the universe!