Pulsars, Black Holes and Quasars

Pulsars

Pulsars are rapidly spinning stars that emit pulses of radio waves at regular intervals. The word pulsar stands for pulsating radio star.

When a big star explodes, its outer shell scatters to form a nebula while its core contracts into a denser star called the neutron star. Its neutrons are tightly compressed and it has extremely high density. Neutron stars are very small and dull. The average diameter of a neutron star is 10 km. these neutron stars are called pulsars.

Radio pulses coming from pulsars produce a tick like sound on radio telescope. Neutron stars like lighthouses in space. Ordinary pulsars flash at an interval of every one or half a second. The most rapid flashing pulsar, NP0532 lies in the crab nebula and emits 30 pulses per second. The oldest and the least frequency pulsar is NP0527 which emits pulses every 3.7 seconds. All pulsars emit pulses at a rate of one pulse per 0.03 second to one pulse per 4 seconds.

Most of the pulsars are not visible through optical telescope. They may be observed with the help of radio telescope. Only two pulsars-NP0532 in the Crab Nebula and PSR 0833-35 in Gum Nebula can be seen with the help of optical telescope. Scientists have so far discovered more than 100 pulsars.

Block Holes

When very big stars, three times bigger than the sun, collapse by the force of their own gravity, some black regions are created in the space. These are called black holes. They have gravitational force so enormously high that no matter, not even light can escape from it.

The first black hole was detected in 1972. It was in a binary star of cygnusx-1 which is a powerful source of X-rays. It is a small member of the binary star, which is completely black. It is not a neutron star and, therefore, it is called black hole. Normally black holes emit X-rays and infrared radiation which help in their detection in space. The mass of black holes may be equal to that of 100 million suns.

Quasars

Quasar is an abbreviated form of quasi stellar radio sources. Quasars appear like a star. Through an optical telescope they look like an ordinary dull star, but radio telescope observations have indicated that they are the source of radio waves. Quasar 3C-273 was discovered by Maarten Schmidt in 1962. The value of its red shift was 0.158. Red shift is an effect of change in frequency and is seen in light will shift towards the violet end of the spectrum, and if the object is moving away, its light will shift to the red end of the spectrum. Red shift indicates that the source of light was receding away.

Quasars emit radio waves and X-rays with light. The size of quasars is 1/1, 00,000 of our galaxy but its brightness is 100-200 times more. So far 12000 quasars have been discovered.