Omega Centauri: Proud cluster or sad remnant? (Forwarded)

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Wednesday, 16 July 2003

OMEGA CENTAURI: PROUD CLUSTER OR SAD REMNANT?

An ANU graduate student who believes the spectacular Omega Centauri star cluster
is not all it seems will challenge prevailing wisdom at the General Assembly of
the International Astronomical Union in Sydney today.

Laura Stanford thinks that Omega Centauri may be the pitiful remnant of a once
enormous galaxy that has been ripped to pieces by the gravity of our own galaxy,
the Milky Way.

Her research, in collaboration with ANU colleagues Dr Gary Da Costa and
Professor John Norris, and Dr Russell Cannon from the Anglo-Australian
Observatory, conclusively shows that some stars in Omega Centauri formed long
after others.

A brilliant cluster of over one million stars in the southern Australian sky and
clearly visible to the naked human eye, the stars of Omega Centauri have long
been thought to have formed billions of years ago, drifting peacefully together
through space ever since.

"For a few years now there have been hints that there was something very strange
about Omega Centauri," Ms Stanford said. "Our new observations show beyond
reasonable doubt that Omega Centauri is not what we all thought it was."

Once the first stars in a cluster are born, some of them explode, which blasts
away remaining interstellar gas, from which stars are made. Even if some of this
star forming gas survived the explosions, Omega Centauri frequently passes
through our own galaxy, the Milky Way, which should strip any remaining gas.

"Once the gas is gone, no stars should form, but we're seeing lots of these
newer stars in Omega Centauri," Ms Stanford said.

According to Dr Da Costa, the team's research will now focus on how the gas
managed to stay inside the galaxy long enough to form the younger stars.

"We are beginning to think Omega Centauri is not a normal star cluster at all,
but that perhaps it was once the centre of a whole galaxy, one hundred times
bigger than the cluster is now.

"This galaxy blundered too close to our own, the Milky Way, and was torn apart
by its gravity -- all we see today are the few stars that once lived in the
middle of this galaxy. The rest have been wrenched away and scattered all over
the sky."

The team used a revolutionary new feature of the Anglo-Australian Telescope to
make their observations -- the 2dF instrument, which allows astronomers to
measure the properties of hundreds of stars at once.

Photographs available.