A pulsar is a rapidly rotating neutron star whose magnetic fields emit charged particles of radiating energy. A pulsar possesses jets of particles streaming from their magnetic poles at the speed of light. These jets produce very intense beams of light. The magnetic and rotational axes of a pulsar are not aligned, therefore, the beams of light created can be observed only if the earth lies on their path, and they´re called pulsars. The rotational period of a pulsar varies from milliseconds to seconds, and the pulses are regular and very precise. Pulsars were first detected as radio signals in the late 1960s.
Discovery of pulsars
One of the first accounts for the detection of pulsar beams of light was made by Jocelyn Burnell and Antony Hewish in 1967. While looking for sources of radio emission in outer space, they detected a signal, consisting of regular pulses of light followed by brief pauses of 1.33 seconds in between. In 1974 astronomers Russell Hulse and Joseph Hooton discovered the first pulsar (PSR B1913+16) in a binary system. The observation of this pulsar gave evidence of the existence of gravitational waves, and as a consequence of their discovery they were awarded the Nobel Prize in physics.
Further observations have revealed another type of pulsars with more rapid periodic rotations. In 1982, a group of astronomers discovered the pulsar (PSR B1937+21) with a spin period of 1.6 milliseconds. These types of pulsars are known as millisecond pulsars (MSPs) and due their name to their rapid and stable rotation. The very precise rate of rotation of MSPs can be compared to the most precise atomic clocks used on earth. The pulsar with the longest rotational period is (PSR J2144-3933) at 180 parsecs from Earth, and a rotational period of 9.437 seconds.
Types of pulsars
There are three distinct types of pulsars, and they´re classified based on the source of electromagnetic radiation. Spin-powered pulsars are those whose source of radiation is the one generated by the rotation of the neutron star. Accretion-powered pulsars are those found in binary systems composed of a regular star and a neutron star; in this system, the strong gravitational force of the neutron star pulls matter from the other star. The material is channeled to the magnetic poles, where they are accelerated, emitting x-rays, which can be observed if they cross the path of the Earth. Magnetars are those that are powered by intense magnetic fields. Magnetar SGR 1806-20 is known to have produced the greatest burst of power in our Galaxy in 2004.
It is believed that x-ray pulsars in binary systems could be the next stage of spin-powered pulsars which have lost angular momentum power, and which only become visible again by obtaining their source fuel from a binary companion. The accretion of material from a companion star to the magnetic poles of the neutron star transfers enough power so as to begin a new rotation cycle powered in milliseconds. The pulses of x-rays can be observed on earth when the rotating beams of light align with the path of earth. The precise emitting pulsations of pulsars often allow astronomers to make other astronomical discoveries.
The discovery of pulsars has allowed astronomers to study the neutron star, where the behavior of matter at nuclear densities can be observed. Pulsars have allowed astronomers to corroborate the theory of special relativity at intense gravitational fields. The precise rotational periods of pulsars have been used by astronomers to make some important observations, including the discovery of extra solar planets. Pulsar maps have been used on two Pioneer Plaques. Two 15 by 23 cm (6 in. by 9 in.) plaques made of gold and aluminum were set on the antennas of both the Pioneer 10 and Pioneer 11, hoping to help identify the position of planet earth by extraterrestrial intelligences.