Pulsars

Discovered by : Jocelyn Bell Burnell and Antony Hewish.

Discovered in year : 1967

Pulsars are highly magnetized, rotating neutron stars that emit a beam of electromagnetic radiation. The observed periods of their pulses range from 1.4 milliseconds  to 8.5 seconds. The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect as it has has a mechanism to beam light just like a Lighthouse. These effect give rise to the pulsed nature of the stars that gives pulsars their name. Because neutron stars are very dense objects, the rotation period and thus the interval between observed pulses is very regular. Pulsars pulse because the rotation of the neutron star causes the radiation generated within the magnetic field to sweep in and out of our line of sight with a regular period. Several hundred pulsars are now known, with periods ranging from seconds down to sub-milliseconds. Two pulsars, the Crab and the Vela Pulsars, are strong sources of gamma rays.

History of the Discovery

The first pulsar was observed on November 28, 1967 by Jocelyn Bell Burnell and Antony Hewish. When they discovered it, they were baffled as it had unnatural regularity of emissions so they dubbed their discovery LGM-1, for "Little Green Men" (a name for intelligent beings of extraterrestrial origin). Their pulsar was later dubbed CP 1919, and is now known by a number of designators including PSR 1919+21, PSR B1919+21 and PSR J1921+2153. Although CP 1919 emits in radio wavelengths, pulsars have, subsequently, been found to emit in visible light, X-ray, and/or gamma ray wavelengths. The word "pulsar" is a contraction of "pulsating star", and first appeared in print in 1968.

Development in the Discovery of Pulsars

The most famous pulsar was discovered shortly after that. It lies in the Crab Nebula (M1), which is about 7000 light years away in the constellation Taurus. The Crab Pulsar rotates about 30 times a second, emitting a double pulse in each rotation in the RF through gamma-ray spectrum. The suggestion that pulsars were rotating neutron stars was put forth independently by Thomas Gold and Franco Pacini  in 1968, and was soon proven beyond reasonable doubt by the discovery of a pulsar with a very short (33-millisecond) pulse period in the Crab nebula.

In 1974, Antony Hewish became the first astronomer to be awarded the Nobel Prize in physics. Considerable controversy is associated with the fact that Professor Hewish was awarded the prize while Bell, who made the initial discovery while she was his Ph.D student, was not. In the same year i.e.1974, Joseph Hooton Taylor, Jr. and Russell Hulse discovered the first time pulsar in a binary system, PSR B1913+16. This pulsar orbits another neutron star with an orbital period of just eight hours. In 1993, the Nobel Prize in Physics was awarded to Taylor and Hulse for the discovery of this pulsar.

In 1982, Don Backer led a group which discovered PSR B1937+21, a pulsar with a rotation period of just 1.6 milliseconds. Observations soon revealed that its magnetic field was much weaker than ordinary pulsars, while further discoveries cemented the idea that a new class of object, the "millisecond pulsars" (MSPs) had been found. MSPs are believed to be the end product of X-ray binaries.

In 1992, Aleksander Wolszczan discovered the first extrasolar planets around PSR B1257+12. This discovery presented important evidence concerning the widespread existence of planets outside the solar system, although it is very unlikely that any life form could survive in the environment of intense radiation near a pulsar.

In June 2006, the astronomer John Middleditch and his team at LANL announced the first prediction of pulsar glitches with observational data from the Rossi X-ray Timing Explorer. They used observations of the pulsar PSR J0537-6910.

Role of the Discovery of Pulsars in the improvement of Human Life

• The study of pulsars has resulted in many applications in physics and astronomy. Striking examples include the confirmation of the existence of gravitational radiation as predicted by general relativity and the first detection of an extrasolar planetary system.

• MSPs can be used by astronomers as clocks rivalling the stability of the best atomic clocks on Earth. Factors affecting the arrival time of pulses at the Earth by more than a few hundred nanoseconds  can be easily detected and used to make precise measurements.

• The discovery of pulsars has allowed astronomers to study an object never observed before, the neutron star. Neutron Star is the only place where the behaviour of matter at nuclear density can be observed (though not directly). Also, millisecond pulsars have allowed a test of general relativity in conditions of an intense gravitational field.

• Pulsar maps have been included on the two Pioneer Plaques as well as the Voyager Golden Record. They show the position of the Sun, relative to 14 pulsars, which are identified by the unique timing of their electromagnetic pulses, so that our position both in space and in time can be calculated by potential extraterrestrial intelligences.