Cosmic Flow of Galaxies Seen Across a Billion Light Years
The Universe is lumpier than current theories suggest and the
Milky Way is part of a massive flow of galaxies moving together at
2.2 million kilometres per hour toward the constellation of Vela in
the southern hemisphere, according to astronomers at the University
of Victoria, the University of Durham, England and Princeton
University.
The group's findings will be reported in tomorrow's edition of
Science magazine and published in the Feb. 20 issue of The
Astrophysical Journal Letters.
These are the first results from the SMAC (Streaming Motions of Abell
Clusters) survey, led by Dr. Michael Hudson of UVic and Dr. Russell
Smith of Durham, with Dr. John Lucey and Prof. Roger Davies (Durham)
and Dr. David Schlegel (Princeton).
It's known that our galaxy and our nearest neighbour, Andromeda, move
at 600 kilometres per second with respect to the distant cosmic
microwave background. But the findings of the SMAC collaboration
suggest that galaxies far beyond our local neighbourhood are also
moving in a similar direction and speed.
The SMAC team observed 699 galaxies in 56 galaxy clusters spanning a
volume of 1.2 billion light years in diameter. Measuring motions
rather than positions of galaxies, the group investigated the
distribution of matter (seen and unseen) in and around this vast
region of space.
So what is doing the pulling? The study means that the Great
Attractor--the region of space once thought to be pulling all
galaxies toward it--may not be the final explanation. "Our survey
goes beyond the proposed location of the Great Attractor and we still
see outward motion of galaxies beyond it," says Hudson.
"We suspect that no single object can be identified as responsible
for the flow," says Smith. "Probably several regions contribute to
the pull on the local region." The two most prominent concentrations
of galaxy clusters are "superclusters" in the southern sky close to
the direction of the observed flow.
The team's survey may also provide clues about dark matter, one of
the great mysteries of the Universe.
"The speed of the galaxy flow and the scale over which it extends
indicate that the Universe is far less homogenous than we had
supposed," says Hudson. "At least 90 per cent of the Universe is
composed of dark matter and the nature of dark matter is unknown.
Popular theories about dark matter predict that the Universe should
be very smooth on these very large scales--so smooth that flows like
this should be extremely rare."
The SMAC team employed telescopes in the Canary Islands, Australia
and Chile. The study is the latest in sometimes contradictory
research into the motion of galaxies. The team, and other groups, is
attempting to resolve and interpret these discrepancies ahead of an
international conference on cosmic flows in Victoria in July.
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Media contacts
Dr. Russell Smith (University of Durham) at 44-191-374-2194
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Keywords: cosmic, flow, galaxies, seen, billion, light, years