Rapid galaxy merging dominates universe's early history (Forwarded)

Public Affairs Office
University of Nottingham
Nottingham, U.K.

More information:

Dr Christopher J Conselice
+44 (0)115 951 5137
www.nottingham.ac.uk/~ppzcc1/

Emma Thorne
Media Relations Manager, Public Affairs Office
The University of Nottingham
+44 (0)115 951 5793

February 17, 2006

PA26/06

Rapid galaxy merging dominates universe's early history

A study by an academic at The University of Nottingham gives us the first
observational evidence for how massive galaxies in our universe formed.

The implications of the study are vast and are being used by astronomers
to explain seemingly unrelated processes such as how massive black holes
and the universe's stars came to be.

The research, led by Dr Christopher J Conselice, of the University's
School of Physics and Astronomy, which is published in the February 20
edition of the Astrophysical Journal, uses the deepest images taken by the
Hubble Space Telescope to study galaxies when they were only two billion
years old. His team has found that the majority of the most massive
galaxies in the early universe are undergoing multiple and spectacular
mergers.

These mergers lead to the creation of new stars from colliding gas clouds
and likely feed and grow the masses of black holes lurking in the centre
of all galaxies.

The work is helping to definitively confirm what scientists have long
hoped for -- massive galaxies form when smaller galaxies merge together --
a major and previously unconfirmed prediction of the cosmological standard
model.

"The results show us that the most massive galaxies we see in today's
universe, which are passive and old, were once undergoing rapid mergers
with each other, which it turns out is how they form," said Dr Conselice.

While distant galaxies have been studied for over a decade, it has until
now remained a mystery how they evolved into the galaxies we see today.

Young galaxies have very low masses and astronomers have long been puzzled
by how these systems turn into massive galaxies in the local universe. The
Conselice results demonstrate that a typical massive galaxy in today's
universe has undergone four to five mergers with other galaxies to
transform from these young low mass systems into the giant galaxies.

These mergers are very rare today, with only about one per cent of
galaxies merging, while 10 billion years ago, nearly all massive galaxies
were undergoing mergers. An analysis technique developed by Conselice for
more than 10 years was used on the deepest images ever taken of the
universe to make these discoveries.

The results further show that massive galaxies did not form rapidly,
within a few million years after the Big Bang, or form gradually over an
extended period of time. In a surprising finding, almost all of this
merger activity occurs over a very short period of time, from the birth of
the universe to about six billion years ago.

Dr Conselice added: "Perhaps the most amazing thing about these results is
that massive galaxy formation is largely over when the universe is half
its current age. This means that all this merging activity was somehow
curtailed by an unknown process."

The research may hold clues about the formation of our own galaxy. The
Milky Way contains spiral arms, which are not thought to form through the
merger process. However, at the centre of our galaxy is a spherical system
of stars called a bulge -- a high-density region featuring many old stars
and a massive black hole -- which probably formed as a result of these
mergers.

The research could also help astronomers to see into the Milky Way's
future -- it is possible that our galaxy will itself merge with Andromeda,
our nearest neighbouring large galaxy in around a billion years from now.
This would see the destruction of the spiral disk that surrounds the bulge
and change dramatically the shape of our galaxy, as well as significantly
altering the positions of stars we see in the night sky.

- Ends -

Notes to editors: The University of Nottingham undertakes world-changing
research and provides teaching of the highest quality. Ranked in the THES
World Top 100 Universities, its academics have won two Nobel Prizes since
2003. An international institution, the University has campuses in the
United Kingdom, Malaysia and China.


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