The great cosmic discovery - VII

Prof H Nandakumar Sarma *

The discovery of microwave background radiation, neutron star, pulsar; trying to understand the cosmic forces, the discovery of anisotropy of cosmic microwave background radiation, the discovery of Higgs boson ( God’s particle ), the detection of gravitational wave and black hole etc are some of the exciting moments in the understanding of the universe.

In this series, we trace some of the great cosmic discovery made from the beginning of the 20th century to the present day.

With the discovery of radio waves coming from Milky Way and other stellar objects by Karl G. Jansky, the exploration of universe by using radio waves gained momentum. Radio astronomy started at Cambridge University in 1945.

From the earliest days the Cambridge radio astronomy group has battled to construct bigger and bigger radio telescope with resolution comparable to those obtained with optical telescope. Martin Ryle at Cambridge developed an entirely different approach - ‘aperture synthesis.’

Martin Ryle was born on September 27, 1918 in Brighton, England. He was educated at Oxford and graduated with a degree in physics in 1939. During the World War II, he worked with the Telecommunications Research Establishment on the development of radar and other system for the Royal Air force.

Shortly after the war, both he and his father received appointments to two of England’s distinguished universities. His father held the first chair in social medicine at Oxford, while Ryle received a fellowship at Cambridge, where he worked on an investigation of radio emissions from the sun.

In 1948, he was given a lectureship in physics at Cambridge and became a Fellow of Trinity College, Cambridge in the following year. At this time, Ryle was joined by Anthony Hewish. During the early part of the 1960’s Ryle implemented his first history making instrument- ‘aperture synthesis’ in radio telescope.

What is aperture synthesis? Aperture synthesis uses small telescopes dishes to produce the angular resolution capability of a much larger telescope dish (a very large dish say diameter of one mile may be technically or financially infeasible).

The method of aperture synthesis keeps one or more small dishes fixed and move one or more other dishes over the earth’s surface. Ryle admitted that he he had been fortunate, since the developments in related fields like low noise amplifier, computer to process the data had all occurred at the right time.

His first radio telescope constructed in 1964 based on aperture synthesis technique was ‘one mile telescope’. The Cambridge one mile radio telescope operated in late 1964 consisted of only three 18metre disc antenna but its sensitivity and resolution was equivalent to a single disc antenna having one mile in diameter.

It enabled to detect extremely faint objects far out in the universe, By counting the relative number of radio sources of different intensities, Ryle and his team showed that the universe appeared to be evolving. The counts of radio sources at great distance are smaller than expected on steady state theory but consistent with big bang model of the origin of the universe.

This fact, coupled with the simultaneous discovery of universal micro- wave background radiation at 3K, finished off the steady state theory. He observed that constellation Cygnus a distant galaxy - 1000 million light years away gives out radio waves about a million times more intense than our milky way.

In 1972, 5 km radio telescope was operated at Cambridge based on aperture synthesis technique. With Ryle’s radio telescope, scientists have been able to detect objects more distant than ever before.

The aperture synthesis techniques used in radio telescope are now being applied to many medical diagnostic instruments like CT scan, Magnetic Resonance Imaging (MRI) and Ultrasonic Imaging etc.