Radio telescopes will tell about the Universe
BLACK HOLES are the darkest objects in
the Cosmos and in our understanding.
Scientists conjecture that these compact
objects are formed when a dying star
explodes and the matter collapses in a
very small region of space. The matter
density is so high that the gravity of the
object is strong enough to prevent light
from escaping out.
Our understanding of black holes
comes from theories of gravitation and
cosmology. Astronomers have extensively studied these by looking at their
effect on other objects. One of the most
important instruments in studying
black holes is the radio telescope.
A new international initiative has
reported the first results from an orbiting radio telescope. These may go on to
revolutionise our understanding of
many of the Universe's 'crazy' objects,
including black holes (Science, Vol 281,
No 5384).
Radio observation of the Cosmos
began when Karl Jansky detected radio
waves from space in 1933. Several powerful telescopes were built over the
years. But the big break came in the
1950s with the development of radio
interferometers, which use wave interference to make precise measurements
of length or displacement. These consist
of two or more widely separated antennae connected by transmission lines.
With their greatly increased resolution,
they can be used to determine the position or diameter of a radio source or to
separate two closely spaced sources.
Another significant step in this
direction is the phase-array telescope,
which consists of a large numbers of relatively small antennae elements
arranged over a relatively large area,
yielding the effective sensitivity and resolution of an antenna much larger than
can practicably be built.
An example of such a system is the
27-antenna Very Large Array near
Socorro, New Mexico, USA, one of the
world's largest and most sensitive
radio telescopes. Use of atomic clocks
and magnetic tapes has allowed scientists to do away with transmission lines
and to use individual telescopes which
are very far away as parts of a radio
interferometer.
Once the hurdle of transmission lines was overcome, it was suggested
that a large telescope be used in space. For this purpose, a radio telescope with a diameter of 8 meters was put into orbit by Japanese scientists in 1997.
This telescope, called the Highly
Advanced Laboratory for Communications and Astronomy (HALCA), is
used complements ground-based telescopes to give a telescope with an effective diameter of over 25,000 km. Its resolution is phenomenal - comparable
to reading this page from a distance of 2,000 km.
The first results from the space observatory have been reported recently. These indicate the presence of massive black holes in the centre of Virgo A,
a very strong radio source which has two
giant radio lobes emanating from it.
The success of this mission has led to astronomers planning even
more ambitious missions like the us National Aeronautical and Space
Administartion's 25-metre orbiting telescope. With these new eyes on the
Universe, we would be closer to explaining some of the outstanding conundrums of the Cosmos.
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