Scientists may soon know what powers quasars
THE WORK done by a team of about 100
astronomers may provide us with the
first hints of the answer to a long-standing query - what powers the starlike
celestial objects called quasars? (Science,
Vol 267, No 5205).
Quasars appear like stars from the
earth, but are as far off as the most distant galaxies - typically, millions of
light years away. To be able to look as
bright as a star at these distances
requires that the quasars produce
immense quantities of energy. For
instance, 3c 273, one of the first quasars
to be discovered, is estimated to be
about 1,000 times more luminous than
our ownigalaxy, the Milky Way.
Quasars, also known as active galactic nuclei, (AGN), are at such large distances from the earth that direct observations are not of much help. Now, a
team of astronomers, called the
International AGN Watch, has used an
indirect method known as reverberation
mapping to study the AGN in a galaxy
called the New General Catalog 5548
(NGc 5548). Reverberation mapping
uses the variations in the radiation coming from the centre of the AGN and those
reflected from the surrounding clouds
of gas.
Using reverberation mapping, the
group tracked the NGC 5548 almost daily
through several telescopes such as the
Hubble Space Telescope, the International Ultraviolet Explorer and a host
of ground-based telescopes. The team
reported that preliminary results provide support for the idea that the gravitational energy of the black hole is the
basic power source of the galaxy's AGN.
It found that the mass of the black hole
in the case of NGc 5548 was about
20 million times the solar mass. The AGN
probably is fuelled by matter beiffg
sucked into the black hole.
The next obvious step is to show
that this result is not a peculiarity of
the NGC 5548 but holds true for other
AGNS as well. But this will involve studying several other AGNs and monitoring
them continuously for longer periods.
In any case, one of the most puzzling
problems in astrophysics could be close
to a solution.
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