What's new about neutron stars

Astronomers on the lookout claim to be finally on target with their observation of what appears to be an old isolated neutron star. This discovery might serve to throw more light on the evolutionary processes of galaxies in general and neutron stars, in particular

Published: Tuesday 30 April 1996

-- (Credit: Illustrations: Vishwajyoti)NEUTRON stars are among the most interesting candidates for observation in the universe. These are super-dense bodies, left behind after the occurence of a supernova explosion which results in the death of an extremely massive star.

Some neutron stars can accrete (combine) material from other stars and thereby turn into bright binary systems radiating enormous quantities of energy. Stars of this particular kind are estimated to number around 100 million to one billion in the universe, but even then they are notoriously difficult to detect because of their extremely faint sources of energy.

However, there are other neutron stars that remain isolated and do not undergo the process of accretion. Newly formed members of the tribe of isolated neutron stars can be easily tracked as they are radio pulsars - stars which give short pulses of radio waves at regular intervals.

But now, Fredrick M Walter, Scott J Wolk and Ralph Neuhauser at the State University of New York in Stony Brook, us and the Max Planck Institute in Garching, Germany, claim to have discovered an old and non-pulsating neutron star. Data gathered by ROSAT (Roentgen X-ray satellite) has been used to identify the star. Walter and his colleagues have identified one source which has all its energy output in the form of soft or low energy x-rays. This rules out almost all other types of objects like active galaxies which usually also radiate at other wavelengths. Furthermore, the source is believed to be very close to us - about 350 light years away.

Though the final word as to whether the source is really an isolated old neutron star is not out yet, astronomers believe this is their best candidate so far. What is needed is better theoretical calculations of the abundance of such stars in our galaxy, as well as improved techniques for their observation. More detections and study of such types of stars will shed, important light on the structure and evolution of neutron stars as well as the chemical evolution of our galaxy.

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