Neutron Stars - Binary, Recycled, and Optical Pulsars


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The most notable pulsars are the Millisecond (period of 0.002 seconds, 31,000 ly, which stands for light-years, has the shortest period); the Black Widow (period of 0.002 seconds, 5,000 ly, a binary pulsar); the Crab (0.033 seconds, 8,100 ly, formed in 1054); the Binary (0.059 seconds, 23,000 ly, also first binary found); the Vela (0.089 seconds, 1,500 ly, also gamma ray source); PSR 1919+21 (1.337 seconds, 2,100 ly, first radio pulsar); J1951+11 (5.094 seconds, 5,400 ly, has longest period); Geminga (0.237 seconds, 520 ly, both an X-ray and gamma-ray pulsar); Hercules X-1 (1.24 seconds, 15,000 ly, an X-ray pulsar); and, Centaurus X-3 (4.84 seconds, 25,000 ly, and first X-ray pulsar).

When a supernova explodes, its death is rebirth in another form. When the outer parts of a star are thrown off into space, the core will collapse causing a neutron star. A neutron star can have a mass the size of our Sun packed inside an area as small as five of New York City's boroughs. Many times these neutron stars become pulsars. Pulsars have intense magnetic and gravitational fields; radio pulsars give off regularly radio wave beats; and, X-ray pulsars will give off regular bursts of high-energy radiation.

Neutron stars are made from a combination of solid and liquid, not gas. Solid iron makes up the outer surface with liquid subatomic particles (neutrons) beneath the surface. The collapsing of the star's core forced electrons and protons to come together making neutrons. These little neutrons are packed tightly together, quite dense, and have a strong gravity. This gravity is so strong that a rocket would need to take off at least half the speed of light to escape from the star's surface. Once a neutron star reaches more than three solar masses, it collapses under its own weight and becomes a black hole.

The pulsars are strong magnetic spinning neutron stars sending out radio waves in regular bursts. The first pulsar was discovered in 1967, and most lie within the Milky Way Galaxy. The fastest pulsar sends out a pulse 642 times a second, and the slowest will give off a pulse every 5.1 seconds. The most recently discovered neutron stars are called magnetars. Their origin is uncertain, but thought to be linked to gamma-ray bursts from space.

When neutron stars send out a radio beam from each end of its magnetic poles, it will spin. The pulse of a radio wave is found each time the beam sweeps past Earth. A spinning neutron star eventually gives off all its energy and slows down. Several million years later, as its spinning slows, it can no longer send out radio waves, and will fade away into the universal sunset.

A binary pulsar is found in orbit around a companion, usually a white dwarf, or another neutron star. Neutron stars have been detected to slowly spiral in toward one another. It is thought that with their eventual collision, a black hole could be the result.

X-ray binaries give off X rays, not radio waves. In a binary system, it will take gas from the companion star, the gas will then be caught by the strong magnetic field where it is sent down funnels onto the neutron star's poles. An X-ray is around 100 million degrees Centigrade and will be formed when the gas hits the surface. Some pulsars give off flashes of light and radio pulses, such as, the pulsar in the Crab Nebula. This pulsar seems to be a star that is flashing on and off for around thirty times a second. The supernova remnant of Vela, blinks eleven times a second.

Radio pulsars that spin rapidly and give off hundreds of pulses every second are thought to be old pulsars that have slowed and died. Once this happened, the old pulsars were spun up again by gas, which fell on them from a companion star, or from a red giant phase. It has been suggested that X-ray binaries are an example of old pulsars being brought back to life.


1. Couper, Heather and Nigel Henbest. Space Encyclopedia DK Publishing, Inc.: NY 1999

2. Editors. Secrets of the Universe. International Master Publishing: US. 1999