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An enormous string of galaxies 300 million light-years long has been
discovered in the remote Universe, challenging existing theories about
how the Universe evolved.
The remote area was formed very early, at a time when the Universe was
a fifth of its present age and the presence of the galaxy string
defies existing models, which can not explain how a string this big
could have formed so long ago.
This is the first time astronomers have been able to map an area in
the early Universe big enough to reveal such a galaxy structure.
ANU astronomer Dr Paul Francis, who coordinated the international
research team, said the galaxy string lay 10,800 million light-years
away. Light travels almost 9.5 trillion kilometres in one light-year,
so our observation of the string is as it appeared 10.8 billion years
ago. The universe was formed during the Big Bang approximately 13.7
billion years ago.
"We have detected 37 galaxies and one quasar in the string, but it
probably contains many thousands of galaxies," Dr Francis said.
"The really exciting aspect of this finding is that it sheds new light
on the formation of the universe. We are looking back four-fifths of
the way to the beginning of the Universe and the existence of this
galaxy string will send astrophysicists around the world back to the
drawing board, to re-examine theories of the formation of the
Universe."
The string was discovered by Dr Francis, Dr Povilas Palunas of the
University of Texas, Dr Harry Teplitz of the California Institute of
Technology, Dr Gerard Williger of Johns Hopkins University and Dr
Bruce E. Woodgate of NASA Goddard Space Flight Center, using
telescopes in Chile and at Siding Spring Observatory in New South
Wales.
The team were refused time on a US telescope because many American
astronomers believed the observations were technically impossible. The
findings have been presented at the American Astronomical Society
meeting in Atlanta.
The team compared their observations to supercomputer simulations of
the early Universe, which could not reproduce strings this large. "The
simulations tell us that you cannot take the matter in the early
Universe and line it up in strings this large," Dr Francis said.
"There simply hasn't been enough time since the Big Bang for it to
form structures this colossal.
"All we are seeing is the brightest few galaxies. That's probably far
less than 1 per cent of what's really out there, most of which is
mysterious invisible dark matter. It could be that the dark matter is
not arranged in the same way as the galaxies we are seeing."
Recently, evidence has accumulated for the presence of dark matter in
the Universe, an invisible form of matter only detectable by the
gravitational pull it exerts on ordinary matter (and light). There are
many possibilities for what dark matter might be, but its true nature
is currently unknown.
In recent years, it had been found that in the local Universe, dark
matter is distributed on large scales in very much the same way as
galaxies are, rather than being more clumpy, or less. But go back 10
billion years and it could be a very different story. Galaxies
probably form in the centre of dark matter clouds. But in the early
Universe, most galaxies had not yet formed, and most dark matter
clouds will not yet contain a galaxy.
"To explain our results the dark matter clouds that lie in strings
must have formed galaxies, while the dark matter clouds elsewhere have
not done so. We've no idea why this happened - it's not what the
models predict," Dr Francis said.
The astronomers say the next step is to map an area of sky ten times
larger, to get a better idea of the large-scale structure. Several
such surveys are currently under way. The research was funded by NASA
and the Australian National University.
Further details and a movie animation of the galaxy string is
available on the Internet at: http://www.mso.anu.edu.au/~pfrancis/string/
CONTACT: Dr Francis is available for interview on 0402 640 364
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