What's new about neutron stars

-- (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.