How Do We Know That Pulsars Are Neutron Stars?

Features

• Neutron stars and pulsars are one of the possible end-stages of a star's life. High mass stars (between four and eight times the mass of the Sun) explode as supernovas when fusion ends in their cores. Following the explosion, the matter of the star collapses down to an extremely dense state in which even the protons and electrons of the star's atoms are compressed into neutrons. The resulting neutron star is small and dense, with high gravity and magnetic fields over one million times stronger than any that can be produced on Earth.

Size

• Among the densest objects in the universe, neutron stars and pulsars consist of a high amount of matter contained in a small diameter. The typical mass of a neutron star is about 1.4 times the mass of the Sun. This mass is contained in a star with a diameter of only about 20 kilometers. With so much mass in so small a space, neutron stars have a gravitational field 200,000,000,000 times that of the Earth.

Effects

• The pulsing of a pulsar is the result of a neutron star's rotation. Because of the neutron star's high magnetic fields, streams of charged and fast-moving particles are emitted from the star's magnetic poles. The magnetic pole of the star is not the same as the rotational pole, so when the neutron star rotates, the stream of particles flashes past at regular intervals. When that particle stream faces our direction, we observe the pulse of the neutron star. The pulsar bursts can be very fast, due to the neutron star's high speed of rotation. The fastest rotation recorded resulted in 642 pulses per second, meaning the body producing the pulses rotated that quickly.

History

• Nuclear physics and astrophysics have predicted the existence of neutron stars since the early 20th century. Pulsars, however, were only first detected in 1967, when a graduate student, Jocelyn Bell Burnell, noted a pulsing radio source. The pulses appeared at regular intervals, indicating a rotating object. When astronomers were able to trace the source of the pulses, they found them to emanate from known locations of neutron stars.

Identification

• Neutron stars are the remnants of stars that have experienced a supernova explosion. In those cases where we have observed a supernova in the past, a neutron star can now be observed. For example, the remnant of the supernova observed in 1054 AD is called the Crab Nebula. At the center of the nebula is a pulsar that emits radiation especially at the X-ray wavelengths.