The world of neutron stars is a quite strange to scientists. Neutron stars are one of the most interesting objects of the universe so far we have observed. Neutron stars are the one of the most exotic objects of the universe. Ordinary matter or stuff we are made of and are familiar with is made of atoms. We know that most of the space in the atoms is empty. Suppose we generate enough force to squeeze the emptiness in the atoms of a rock roughly of the size of a football stadium. After applying this force and removing the emptiness of atoms, leaving no space between the electrons and nuclei, the stone will be squeezed down to the grain of a sand but still weighed 4 million tons. Suppose an island that dense instead of a grain of sand, but the size of an island is 20km. That is a neutron star.
Neutron stars are created when a massive star runs out of fuel and collapses. As the star collapses the density becomes so enormous that electrons and protons are squeezed together to form neutrons. The end result of this squeezing process of electrons and protons is a Neutron Star of 20 km wide but more massive than our sun and is mostly consist of neutrons. These exotic objects possess enormous gravitational field one hundred billion times stronger than we feel on earth. Neutron stars have very strong magnetic field. Neutron stars are tiniest stars known to exist in the universe. Among all the known neutron stars 5% are members of binary system. The companion of a neutron star in a binary system could be either white dwarfs, ordinary stars or other neutron stars. The formation of neutron star in a binary system is quite complicated process. There are about 2000 known neutron stars in the Milky Way and the Magellanic Clouds.
The majority of observed neutron stars in the Milky Way and the Magellanic Clouds are radio pulsars. If the star that has gone for supernova has mass 8 to 20 times of the sun than the core of the star will form neutron star. If the star has a mass less than 8 times to that of the sun than the star after completely burning its fuel will result a white dwarf. Stars more than 20 times massive than sun will result a black hole. The neutron star has mass 1.5 to 3 times to that of sun. Due to the conservation of angular momentum neutron stars starts to spin very rapidly. This is a pulsar. A pulsar is a spinning core of a star that has collapsed into neutron star. There is a type of neutron stars that can rotate more than 100 times per second.
Original star before supernova event has magnetic field and after collapsing to a neutron star the magnetic field become stronger. When these magnetic fields rotate along with the neutron star, they produce radio waves shooting out of the North and South Pole of the neutron star. In general the direction of this radio beam is not actually along the same axis that the neutron star is spinning on. Due to this we can observe them with radio telescopes. Milliseconds pulsars also produce gamma rays. Fermi Telescope launched by NASA has detected many pulsars. This telescope is actually mapping the whole sky in gamma rays and gamma rays are even more energetic than X-rays.
Many young pulsars emit gamma rays and it’s a common fact among scientists. Fermi has observed that all the millisecond pulsars produce gamma rays and this was a surprise to many scientists. Some physicists long before this observation have already theoretically predicted that we may see gamma rays from millisecond pulsars.