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.
More information
Dr Amanda Bauer (ARC Super Science Fellow, Australian Astronomical
Observatory)
T: +61 2 9372 4852
M: +61 447 029 368
amanda.bauer@aao.gov.au
Media assistance: Helen Sim
T: +61 2 9372 4251
M: +61 419 635 905
hsim@aao.gov.au
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
Publication
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
Images
Visualization of the Aquarius Stream of
stars in our Galaxy.
Credit: Arman Khalatyan, AIP
http://eos.aip.de/arm2arm/RAVE/presse/images/FaceOn01.jpg
Animation
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
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