What is Pulsar ?

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.

Other scientists suggested several other more plausible hypotheses about the nature of pulsars. Among them was Austrian astrophysicist Thomas Gold’s (1920–2004) hypothesis that pulsars were produced by neutron stars.

There have been a total of 1600 found so far, and the fastest discovered emits 716 pulses a second.

Neutron stars had never been observed, but their possible existence had been suggested by American physicist J. Robert Oppenheimer (1904–1967) and George M. Volkoff in 1939 as a final remnant of a supernova explosion, where a massive star explodes and ejects most or nearly all of its mass

Later on, pulsars were found in binary systems, which helped to confirm Einstein’s theory of general relativity.

However, if the remnant’s mass is more than 1.4 solar masses, its gravity will cause the remnant to collapse beyond the white dwarf stage, forcing free electrons into atomic nuclei and forcing them to combine with protons to form neutrons.

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.

The collapse is finally stopped by the rigidity of nuclear matter; here about 1.5 solar masses is squeezed into a body with about a 6.2 mi (10 km) radius.

When a pulsar first forms, it has the most energy and fastest rotational speed.

Support for Gold’s neutron star model for pulsars came in 1968 when a very fast pulsar (which emits pulses every 0.33 second) was discovered in the Crab Nebula, the gaseous ejecta from a supernova observed by Chinese scientists in 1054.

As it releases electromagnetic power through its beams, it gradually slows down.

Subsequent observations showed that this pulsar emits pulses at wavelengths from gamma rays through visible light to radio waves. Gold’s model has the neutron star rotating very fast, with its rotation period equal to the interval between pulses; only a neutron star could withstand such rapid rotation without disruption.

Within 10 to 100 million years, it slows to the point that its beams shut off and the pulsar becomes quiet.

Pulses are thought to be produced by radiation beamed towards the solar system from charged particles moving in a strongly compressed magnetic field near the pulsar.

When they are active, they spin with such uncanny regularity that they’re used as timers by astronomers.

Additional support for the neutron star model came in 1987 at the start of the observed outburst of Supernova 1987 in the Large Megellanic Cloud, when bursts of neutrinos were detected simultaneously at two widely separated underground observatories (in Japan and Ohio, United States).

In fact, it is said that certain types of pulsars rival atomic clocks in their accuracy in keeping time.

The theory of supernovae predicts that most of the gravitational energy released during the collapse of a supernova remnant to form a neutron star will be converted to neutrinos. The observed supernova bursts support this theory.

Pulsars also help us search for gravitational waves, probe the interstellar medium, and even find extrasolar planets in orbit.

Extremely fast pulsars, which emit pulses at intervals from one to several milliseconds, were discovered in the 1980s. Several of them were found to be members of binary star systems with very short periods of revolution.

This has led to speculation that millisecond pulsars are formed by the merging of a neutron star and another star in a binary system, where the transfer of mass and angular momentum onto the neutron star “spins it up.”

In fact, the first extrasolar planets were discovered around a pulsar in 1992, when astronomers Aleksander Wolszczan and Dale Frail announced the discovery of a multi-planet planetary system around PSR B1257+12 – a millisecond pulsar now known to have two extrasolar planets.

The distances to most pulsars are uncertain. The nearest estimated distance for a pulsar, is about 280 light-years.

It has even been proposed that spacecraft could use them as beacons to help navigate around the Solar System.

All other pulsars seem to be considerably more distant. The Crab Nebula pulsar and the 17 pulsars that have been found in 11 globular clusters have somewhat more reliable distance estimates, but there are thousands and even tens of thousands of light-years from the solar system.