Pulsars
Written by Fraser Cain
The Crab Pulsar. This image combines optical data from Hubble (in red) and X-ray images from Chandra X-ray Observatory (in blue).
Pulsars are types of neutron stars; the dead relics of massive stars. What sets pulsars apart from regular neutron stars is that they're highly magnetized, and rotating at enormous speeds. Astronomers detect them by the radio pulses they emit at regular intervals.
The formation of a pulsar is very similar to the creation of a neutron star. When a massive star with 4 to 8 times the mass of our Sun dies, it detonates as a supernova. The outer layers are blasted off into space, and the inner core contracts down with its gravity. The gravitational pressure is so strong that it overcomes the bonds that keep atoms apart. Electrons and protons are crushed together by gravity to form neutrons. The gravity on the surface of a neutron star is about 2 x 1011 the force of gravity on Earth.
Pulsars are simply rotating neutron stars. They're actually blasting out energy from their magnetic poles, but they're spinning so rapidly that we see the blasts of radiation in regular intervals; sort of like the beams from a light-house.
The first pulsar was discovered in 1967, and it surprised the scientific community by the regular radio emissions it transmitted. These emissions were so regular that some astronomers thought it might be evidence of communications from an intelligent civilization. Astronomers theorized that they were rapidly rotating neutron stars, and this was further supported by the discovery of a pulsar with a very short period (33-millisecond) in the Crab nebula.
Later on, pulsars were found in binary systems, which helped to confirm Einstein's theory of general relativity. And in 1982, a pulsar was found with a rotation period of just 1.6 microseconds. In fact, the first extrasolar planets ever discovered were found orbiting a pulsar – of course, it wouldn't be a very habitable place.
There are now more than 1,500 known pulsars.
We have written many articles about stars here on Universe Today. Here's an article about a newly discovered gamma ray pulsar, and here's an article about how millisecond pulsars spin so fast.
Want more information on stars? Here's NASA's World Book on Stars, and more information from NASA's imagine the Universe.
We have recorded several episodes of Astronomy Cast about stars. Here are two that you might find helpful: Episode 12: Where Do Baby Stars Come From, and Episode 13: Where Do Stars Go When they Die?
Filed under: Astronomy
