Cosmologists take a closer look at how gravity is strangling an expanding universe
COSMOLOGY is somewhat of an oddball
among the physical sciences. Experimental facts about the origin and the
ultimate fate of the universe are usually
scarce, making cosmology a concoction
of theory, some facts and much speculation. However, the scenario has undergone a change in the recent past because
of the availability of better equipment.
The accurate measurement of microwave background radiation by the
Cosmic Background Explorer (com)
satellite in 1993 has proved that cosmologists can have access to good and reliable experimental data (Science, Vol
269, August 11, 1995).
One such cosmological aspect
which has proved difficult to measure
has been the deceleration parameter q0.
This is an extremely important cosmological quantity, being a measure of how
fast the pull of gravity is slowing down
the expansion of the universe.
Applying different techniques, some
groups of astronomers working at
Caltech in Pasadena, California, Lawrence Berkeley Labs in Berkeley,
California and Harvard-Smithsonian
Center for Astrophysics in Cambridge,
Massachusetts are now trying to mea-
sure the value of the elusive deceleration
parameter. The Berkeley group, for
instance, is using type IA supernovas,
stars which are exploding with immense
energies and having roughly the same
actual brightness. This point is crucial
because to measure q0, "standard
candles" - sources whose apparent brightness can be taken as a
measure of their distance - are
needed. Comparing the distances of
these objects with their redshifts
(the change in the colour of the
light from them because of their
velocity away from the earth) to see
how much the relation is distorted
will give hints of the presence of
cosmic deceleration.
Other methods of measuring
the deceleration parameter include
using radio galaxies as standard
candles and looking at giant voids
in the distribution of galaxies. For
the more ambitious, plans are afoot
to Use the LIGO gravity wave detector (a
series of wave detectors around the
world) when it will appear in 1999 to
study pairs of neutron stars for measuring the q0. Astronomers, however,
feel that conclusive data will be unavailable for quite some time. Till then, the
fate of our universe will remain open to
speculation.
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