One of the world's largest radio telescope being set up near Pune will look for incontrovertible evidence for the Big Bang theory on the origin of the universe.

Published: Saturday 15 January 1994

QUESTIONS on the origin of the universe have mystified philosophers and astronomers alike. Now, thanks to a Herculean effort by scientists and engineers working on the Giant Metrewave Radio Telescope (GMRT) project of the Tata Institute of Fundamental Research (TIFR) in Bombay, astronomers may soon get a glimpse of what happened 15 to 18 billion years ago.

Located about 90 km north of Pune, the GMRT "is a frontline research facility for astronomy and astrophysics," says Govind Swarup, professor of eminence at TIFR and director of the project. When completed in 1994, this telescope will be the largest of its kind in the world.

The GMRT will receive radio waves from various celestial objects and convert them into images. Objects in space radiate various electromagnetic waves such as X-rays, visible light, ultra-violet and infrared rays and radio waves, depending on physical conditions such as temperature and the magnetic field. Radio waves generally emanate from strong electric and magnetic fields that are created in the aftermath of star explosions and in the ultra-strong gravitational fields in the central regions of galaxies.

The GMRT will detect radio waves mainly with a wavelength of one metre from bodies such as quasars and pulsars. But it is also capable of operating at six different wavelengths from about 20 cm to as much as 8 metres -- a range never studied before, says Swarup. As a result, the telescope will open a window to phenomena in the universe never observed before.

Scientists will use the GMRT to find conclusive proof for the Big Bang theory, according to which a massive explosion some 20 billion years ago gave birth to the universe that has since been expanding and cooling. Astronomers have discovered that the universe is indeed expanding as they have observed galaxies speeding away from one another. Recently, background microwave radiation predicted by the theory was also detected. To clinch the argument in favour of the theory, scientists are now searching for neutral atomic hydrogen, which is believed to have led to the formation of galaxies.

Neutral hydrogen emits radio waves of 21 cm wavelength, but scientists believe the expansion of the universe has stretched the wavelength of this primordial element to almost a metre. Evidence of this hydrogen is what astronomers hope to find using GMRT.

The bigger the better Because metre-wavelength radio waves emitted by distant objects are extremely weak, massive dish antennae -- similar to those used to receive satellite television in households but several times larger -- are necessary to collect and focus them.

The GMRT consists of 30 such dish antennae, arranged in a Y-shaped configuration. Six dishes are placed along each of the 14 km-long lines that make up the Y and 12 dishes are randomly spaced at a distance of one km from each other at the centre of the Y.

The project is unique in another way as well. On the plains where the antennae are to be raised, wind speeds can be as high as 155 km per hour. To enable the dish antennae to withstand the high winds, the scientists developed the Stretched Mesh Attached to Rope Trusses (SMART), in which the reflecting surface of the antenna is made of thin stainless steel wires -- not solid steel -- stretched across parabolic frames. Besides allowing free passage of winds, SMART is lighter and its rough reflecting surface is expected to be more suited to detecting longer wavelengths.

Indigenous electronics
The telescope uses indigenously developed state-of-the-art electronics. A powerful parallel processing computer, developed in collaboration with the Centre for the Development of Telematics, will convert the radio signals into images.

Besides looking for atomic hydrogen, astronomers plan to set the giant telescope on pulsars -- rapidly rotating and extremely dense stars that were discovered in 1967. Closer home, the GMRT will be used to study radio signals with metre wavelengths from objects in the Milky Way and other nearby galaxies.

Radio waves from the sun and planets in the solar system will also be studied. Swarup says the project will explore the very fundamentals of our existence and reckons that some observations could well be made by astronomers by 1994, and...the universe is the limit.

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