The Hubble Space Telescope detects some of the oldest galaxies in the Universe
THE Hubble Space Telescope (HST) has
never failed to surprise us. A team of us
astronomers have recently used it to discover what may be the oldest and farthest galaxies ever seen. This will have a
serious impact on the theories on the
evolution of the Universe and formation of galaxies. The so-called Deep
Field exposure was taken in 1996 when
the HST looked at a patch of sky for 10 days. Scientists need to look at a particular patch for such a long time since
most of the galaxies, our cosmic 'neighhours', are many light-years away. This
astronomical distance implies that they
are extremely faint and almost invisible,
even to a powerful telescope such as the
HST. The observed galaxies are 11.7-odd
billion years old, and that makes them
ancient, even by the standards of the
Universe.
The stars in these galaxies were originally shining in ultraviolet light, but the expansion of the Universe 'redshifts' the
light into the visible wavelengths- The
expansion of the Universe is pushing all
objects away from each other. The further the object, the faster is the receding.When a receding object emits light at a
certain wavelength, the light observed
by us has a longer wavelength because
the source is moving away from us. This
phenomenon is exactly like the change
in the pitch of the whistle from an
approaching or a receding train.
The detectors on the HST, however,
would not have seen objects whose light
had redshifted even more -and hence
were farther off- into the infrared
region. To detect these, R Thompson
and his team at the Steward Observatory
in Arizona, USA, looked at the same
patch of the sky using the HST's infrared
detector.
The detector, termed NICMOS,
looked for 36 hours at a part of the original patch containing some 300 visible
galaxies- The results were astonishing.
The team found 100 more galaxies out
of which about 10 were among the farthest objects known to us.
The enormous distance can be
gauged from the fact that if we believe
the Universe to be about 13 billion years
old, then these galaxies go back to some
12.7 billion years. Though the objects
have been spotted, the details are still
missing. They are too far away to give us
information about their shape and composition. For that we will have to wait
for the Next Generation Space
Telescope, slated to be launched sometime in the next decade. But even without details, the finding throws up very
intriguing questions regarding our current understanding of how galaxies
formed. In a few million years after the
birth of the Universe, how matter could
have organised into well-formed galaxies is something that is going to
puzzle cosmologists since most theories
do not favour such rapid formation of
galaxies (Science, Vol. 282, No 2138).
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