A neutron star is the leftover of the gravitational collapse of a massive star. The collapse of this type of stars causes matter to acquire the density of the atomic nucleus. The density of a neutron star is so compacted that several thousand planets the size of the earth would easily fit into a neutron star. The size of a neutron star is typically between 1.4 and 2 solar masses, with about a radius of 12 km (7 miles). During the first stages of their formation, neutron stars rotate very rapidly and emit electromagnetic radiation, therefore, they´re called pulsars.
Star´s life cycle
Typically, a star radiates energy from the nuclear reactions occurring inside their core. This process is called fusion reaction, and it´s the process by which one atomic element is transformed into another, generating great amounts of energy. In the fusion process inside a star, hydrogen is transformed into helium. Over time, a star runs out of nuclear fuel and dies. The next stage in the star´s cycle depends of how big it is. Low mass stars become white dwarfs. When massive stars of between 2-4 solar masses end their life cycle, they collapse under their own gravity so that protons and electrons combine to form neutrons, and the end result is a neutron star. Other stars with bigger masses may collapse under their own gravity, reaching zero density and become black holes.
How a neutron star is formed
The creation of a neutron star is related to a type 11 supernova event. During the event of a supernova explosion, the core of a massive star is compressed, and collapses under its own gravity; the electrons and protons combine to form neutrons and neutrinos. The core of the star attains tremendous density, such, that over time, the density reaches the same as that of the atomic nucleus; at this stage the collapse stops abruptly and a shock wave is produced, causing the outer layers of the star to be blown out into space. The leftover of this explosion is a neutron star. Stars of 1.4 to 3 solar masses usually end up as neutron stars.
During the first stages of formation, a neutron star attains a rotation periods of between 1.3 to 30 seconds. The very high density of a neutron star also determines its high surface gravity. The force of gravity on a neutron star would cause an object at about 1 meter (3 ft.) off the neutron star to crash down on its surface in only one microsecond at the speed of 2000 km (1242 miles) per second. The scape velocity of a neutron star is about one third the speed of light. A neutron star is so dense and compacted that if a spoonful of matter from a neutron star could be obtained, it could contain the mass of the entire population on Earth. A neutron star has 1.4 the mass of the Sun, although just 10 km (6 miles) in radius.
At the beginning of its formation, a neutron star spins rapidly, conserving their angular momentum. Particle acceleration at the magnetic poles causes it to produce emissions of x-ray and radio pulsations, which usually occur at the same rate of rotation, thus, occurring periodically. Neutron stars that emit this type of pulsations are called pulsars. The rapid rotation of a neutron star, along with the strong magnetic field generated usually helps astronomers locate neutron stars in outer space. One of the neutron stars with the most rapid rotation periods is PSRJ1748-2446ad, which rotates at the speed of 716 rotations every second.
While observing the explosion of a supernova in 1934, astronomers Fritz Zwicky and Walter Baade suggested the existence of a neutrons star. In the present, astronomers have recognized more than 2000 neutron stars, of which the majority are pulsars. Approximately 5% of all neutron stars form part of a binary system; the star companion of a neutron star can be a typical star, a white dwarf, another neutron star, or even a black hole. According to nasa.gov, the strong gravitational force of a neutron star pulls matter from its companion star. The material is concentrated in the magnetic poles of the star, and when they heat up, they produce x-rays which can be seen from earth everytime the neutron star rotates.