Tuning in on the Stars:

The fact that stars emit radiowaves was discovered accidentally in  1932  by  a young engineer Karl Jansky. He was trying to find the source of  noise in  a transatlantic telephonic link. He made an experimental radio receiver set to study this problem. To his surprise, he found that the disturbance was due to radiowaves coming from the Milky Way Galaxy. This w2s the beginning of  radio astronomy, i.e.  the study of  cosmic objects through radiowaves emitted by  them. The radio telescope, a basic tool of  radio astronomy, collects radiations from space in the radiowave  region. One of  the largest radio telescopes  in the world was designed and set up by  Indian astronomers at Ootacamund.

The other radio telescopes in  India are stationed at Gulmarg, Ahmedabad, Gauribidanur near Bangalore. Radio telescopes may be  tuned to receive radiowaves of  the desired wavelength in the same way as we  tune a radio to receive only the station we want. Radio telescopes not only give a 'view'  of  the invisible universe, but can also probe much deeper into space when compared with optical  telescopes. Radiowaves can propagate through dust clouds in space,  just  as radio signals on the Earth can penetrate cloudy or foggy weather. Thus, they enable'radio astronomers to construct images of regions completely hidden from the view of  optical telescopes. However, radio telescopes normally receive radiation within a narrow band of wavelengths. Radio telescopes have led to the discovery ot hundreds of cosmic objects that emit radiowaves. Most of  these could be identified with the objects seen by optical telescopes. With the help of  radio telescopes objects like pulsars were discovered. Pulsars are stars that send out pulses of  light and radiowaves in regular bursts. For example, a pulsar in the centre of  the Crab nebula at a distance of  6000 light years from the Earth sends out bursts of  light and radiowaves 30 times a second. Certain radio sources like 3c273,  detected by  radio telecopes and  later examined by optical telescopes, were  named  quasars.

Quasar. an abbreviation of 'quasi-stellar  radio source', is a star-like object situated billions of  light years away. Not  all quasars are radio sources. Since  the electromagnetic waves from quasars are being detected on the Earth, they must be sending out huge amounts of  energy. Quasars are comparatively small  in  size, only about a  light month  across. That  is,  if  youimagined the Milky Way Galaxy to be a football field, a quasar would appear like a grain of  sand. But it emits 100 times more energy than the entire Milky Way Galaxy. Scientists have also found that many elliptical galaxies  that seemed unimportant when