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