A neutron star is an extremely compressed star with high densities similar to those found in the nucleus of an atom. The densely, compacted neutron star could contain in its interior thousands of earth-like planets. The size of a neutron star is about the size of a small city with a radius of 12 km (7 miles). At the beginning of their formation, neutron stars spin rapidly, emitting radio and x-ray pulsations, therefore, they´re called pulsars.
Life cycle of a star
After a star is formed, it usually goes through tremendous energy generating processes known as nuclear reactions. During this stage, a star generates energy through a process known as fusion reaction. In fusion reaction, one element, such as hydrogen is turned into helium, generating very high amounts of energy. Over time, this energy is used and the star begins to die. When a star arrives to this stage, its mass determines how a star will continue to exist. Low mass stars tend to become white dwarfs. Stars with a mass of up to 5 solar masses collapse and form neutron stars. More massive stars may collapse until reaching zero density level and become black holes.
How a neutron star is formed
The initial formation of a neutron star begins during the event of a supernova type II. During the explosion of a supernova, the outer envelope of a star is blown up into space. The remaining iron core continues to collapse until matter is compacted to nuclear densities, forming neutrons and neutrinos. Neutrinos eventually scape to outer space, leaving a core formed almost entirely of pure neutrons. At this stage, neutron degeneracy pressure prevents the star from continuing collapsing. The density reached by a neutron star at this stage is of 1.5 to 3 times the mass of the Sun, although the radius of a neutron star is only 12 km (7 miles).
The density of a neutron star varies with increasing depth, reaching higher densities than an atomic nucleus deeper inside. A neutron star could contain one half million earth-like planets within. Due to the high density within a neutron star, its surface gravitational force is very high, as well. The force of gravity on the surface of a neutron star would force an object within one meter off its surface to fall back to its surface in one microsecond at the tremendous speed of 2000 km (1242 miles) per second. If a three story building could be reduced to attain the density of a neutron star, it would be the size of a small sand grain.
At the beginning of their formation, neutron stars spin rapidly, emitting radiating energy, and they´re called pulsars. The accelerated particles at the magnetic poles produce pulsations of radiating energy in the form of radio and x-ray emissions. These pulsations occur typically at the same rate of the star´s rotation. The rapidly rotation of pulsars and their magnetic fields often allow astronomers to locate them in the universe. One of the fastest rotating neutron stars discovered is PSRJ1748-2446ad, which is located in a the globular cluster Terzan 5 in the constellation of Sagittarius, and spins at a rate of 716 rotations per second.
Scientists were able to deduce the existence of neutron stars after the observation of a nova explosion in 1934. To date, astronomers have discovered up to 2000 neutron stars, some of which a high percentage are pulsars. It is estimated that an approximate 5% of all known neutron stars are part of binary systems. According to nasa.gov, there are two types of pulsars: accretion-powered pulsars and spin-powered pulsars.