Lessons Overview : Neutron Stars and PulsarsA neutron star is the result of the death of a giant star (eight to fifteen times as massive as our sun). When the star runs out of fuel and explodes in a spectacular supernova, all that remains of the star is the dense inner core. As the core continues to rotate and shrink, the protons and electrons in the core get crushed together by the immense gravity and combine to form neutrons. Once this occurs, the core becomes a neutron star.
Neutron stars rotate very fast and are extremely small for celestial objects, measuring only about ten to fifteen kilometers in diameter. However, their masses are approximately the mass of our sun. When an object as massive as the sun is compressed down to the size of a small city, the resulting density is enormous. Because of their enormous masses and high densities, neutron stars have extremely strong gravitational fields. They also have extremely strong magnetic fields. However, the poles of the magnetic field are not necessarily aligned with the axis of rotation. It is this phenomenon that explains the behavior of pulsars.
The magnetic field of a neutron star has the north magnetic pole on one side and the south magnetic pole on the other. Charged particles trapped in the star's magnetic field accelerate, releasing radiation, which results in beams of radiation coming from the magnetic poles. As the neutron star rotates, the beams sweep around like a lighthouse. If a beam sweeps by us here on Earth during its rotation, we detect it as a brief increase in the strength of the radio signal from that point in the sky, producing a regular series of pulses occurring at steady time intervals.