14 February 2011
 |
 |
Dr Mary Williams
(AIP). |
Visualization of
the Aquarius |
Astronomers using a telescope in eastern Australia have identified the shredded
remains of a dwarf galaxy 'buried' inside our own as they seek to better
understand how our Galaxy has grown over time.
"Models of how galaxies evolve predict that big galaxies like ours
will be surrounded by lots of little ones," said Professor
Fred Watson of the Australian Astronomical Observatory.
"But we don’t see enough of those little ones," he said.
"Why? Well, perhaps many of them have been eaten up by the big galaxies.
So, we're looking at our Milky Way Galaxy to try to find little galaxies
that it's swallowed."
Professor Watson is Project Manager for the 10-nation RAVE (Radial Velocity
Experiment) collaboration that found the 'buried' galaxy. RAVE runs on a
1.2-m telescope of the Australian Astronomical Observatory and has so far
measured the velocities of 385 000 stars.
Led by New Zealand scientist Dr Mary Williams, some RAVE team members analysed
the movements of 12 000 stars in the disk of our Galaxy — the flat,
starry part away from the Galaxy's centre. Among the stars, they noticed
15 that were moving anomalously, at speeds of up to 15,000 kilometres per
hour.
Analysis showed that they were part of a large stream of stars, originating
from a small galaxy that ours had dismembered about 700 million years ago.
Most of the stars in the stream lie in the direction of the constellation
of Aquarius, so the group has been called the Aquarius Stream. It covers
an area of the sky about 1300 times the size of the full Moon.
About 15 other star streams have been found in our Galaxy. Most arc up out
of the Galactic plane into much emptier space, and so have been easier to
spot. By contrast, the Aquarius Stream was revealed only by careful 'digging'.
"It was right on our doorstep," said Dr Williams, "but we
just couldn't see it."
Professor Joss Bland-Hawthorn of the University of Sydney, a member of the
RAVE team, said "RAVE is the first of a new class of million-star surveys
that will tell us a huge amount about the ancient origins of the Galaxy.
We expect to find more such infalling dwarf galaxies."
The countries taking part in RAVE are Australia, Canada, Germany, France,
Italy, the Netherlands, Slovenia, Switzerland, the UK and the USA. Professor
Matthias Steinmetz, Director of the Astrophysical Institute Potsdam (AIP)
in Germany leads the collaborative effort.
The Australian Astronomical Observatory is our national optical observatory,
and is part of the Commonwealth Department of Innovation, Industry, Science
and Research. It operates the 3.9-m Anglo-Australian Telescope and the 1.2-m
UK Schmidt Telescope at Siding Spring Observatory in New South Wales.
Professor Fred Watson, Australian Astronomical Observatory
Contact via Helen Sim
Mob: 0419 635 905
Office tel: 02 9372 4251
Email: hsim@aao.gov.au
Professor Joss Bland-Hawthorn, University of Sydney
Mob: 0406 973 133
Office tel: 9351 2621
Email: jbh@physics.usyd.edu.au
Dr Mary Williams, Astrophysical Institute Potsdam, Germany
Tel.: +44 139 242 1964 (office phone - with UK country code)
Mobile (with international roaming): +49 1767 7585 354 ("+49"
is the country code for Germany)
Email: mary@aip.de
Williams et al., Astrophysical Journal,
728-2, 2011.
HTML version: http://iopscience.iop.org/0004-637X/728/2/102/
PDF version: http://www.aao.gov.au/press/aquarius/Aquarius_stream_paper.pdf
Helen Sim
+61 2 9372 4251 (office in Sydney, Australia)
+61 419 635 905 (mob.)
hsim@aao.gov.au
Visualization of the Aquarius Stream of stars
in our Galaxy.
Credit: Arman Khalatyan, AIP
http://eos.aip.de/arm2arm/RAVE/presse/images/FaceOn01.jpg
Visualization of the Aquarius Stream of stars
in our Galaxy.
Credit: Arman Khalatyan, AIP
http://eos.aip.de/arm2arm/RAVE/presse/images/Aquarius_Stream_Rotate.avi
