to 0100 AEST Friday 2 April 2004
contacts and image URLs at
Astronomers discover dozens of
using the Anglo-Australian Telescope (AAT) at Siding Spring Observatory
have found more than forty previously unknown miniature galaxies.
finding will be announced at the Royal Astronomical Society National Astronomy Meeting at the Open
Keynes (UK), on Thursday 1 April.
team of 12 scientists from five countries found the objects, so small
looked like stars, hidden in the nearby Fornax cluster of galaxies.
Fornax cluster is 60 million light-years away – in astronomical terms,
project team leader Dr Michael Drinkwater of The University of
said the galaxies belonged to a class dubbed "ultra-compact dwarfs"
(UCDs), which was unknown before the same team of astronomers
discovered six of
them in the Fornax cluster in 2000.
the researchers say that UCDs outnumber the “conventional” elliptical
spiral galaxies in the central region of the Fornax cluster and they
some in the Virgo galaxy cluster too.
likely that at least some are left-over examples of the primordial
blocks that formed large galaxies by merging together,” said Dr
UQ’s School of Physical Sciences.
could be that they are very common but scientists have overlooked them
they resemble nearby stars at first sight.”
“Obviously, it is very important
that we have a complete inventory of all galaxy types if we want to
accurate knowledge of how much luminous (and even dark) matter is in
universe, as well as understand all the ways in which galaxies are
is very exciting – it will significantly advance our
understanding of how galaxies form and evolve in environments where
surrounded by swarms of other galaxies,” said Professor Joss
the Anglo-Australian Observatory.
simulations predict that there should be thousands of
such small objects in the vicinity of our own Galaxy but we see only
twenty,” he said.
missing objects may be composed of dark matter and therefore
presently invisible to us. Or the simulations could be profoundly
is an area of intense debate in astrophysics.”
were discovered by chance when Dr Drinkwater, Dr Stephen Phillipps of
University and their colleagues undertook a large survey of all the
bright objects they could see in the direction of the Fornax cluster.
UCDs were first discovered with the 3.9m Anglo-Australian Telescope
(AAT) at Siding Spring Observatory, Coonabarabran.
key to finding them was the AAT’s Two Degree Field (2dF) instrument,
which can measure the redshifts (distances) of 400 objects
were able to measure the redshift of every object in the field of
view, and so sort out which objects
that looked like stars in our Galaxy were in fact in the Fornax
team member Professor Warrick Couch of UNSW.
2dF system makes the Anglo-Australian Telescope one of only a handful
world where this kind of observation is possible.”
observations with the Hubble Space Telescope and the European Southern
Observatory’s Very Large Telescope (VLT) revealed just how strange the
Compact Dwarfs are. Although their masses are similar to those of
known dwarf galaxies, they are amazingly small — only about 120 light
of millions of stars are squashed into what is a tiny volume by galaxy
the idea that UCDs are the nuclei of galaxies that were originally
have been stripped of their outer stars, the team predicted that they
find them in other dense clusters where the stripping or "threshing"
process could go on. They also calculated how many more they would
find if they searched for fainter ones.
they put their predictions to the test, three nights of observations
a further 46 UCDs in Fornax — even more than the team had expected —
just four hours they found eight in the Virgo cluster, again around 60
light years away.
results indicate that UCDs are indeed common and part of the standard
population of galaxies we can expect in rich galaxy clusters," Dr
UCD collaboration is: Dr Steve Phillipps of the University of Bristol
Michael Drinkwater of The University of Queensland (joint project
Bryn Jones of Queen Mary University, London; Dr Michael Gregg of the
of California, Davis; Professor Warrick Couch and Dr Kenji Bekki of the
University of New South Wales; Dr Quentin Parker of Macquarie
Sydney and the Anglo-Australian Observatory; Ms Anna Karick of the
of Melbourne; Mr Russell Jurek of The University of Queensland; Dr
Bridges of Queen's University, Ontario; Dr Harry Ferguson of the Space
Telescope Science Institute, Baltimore; and Dr Michael Hilker of the
The work has received Australian
Research Council funding of $180,000 for a two-year program.
For more information
Michael Drinkwater, University of Queensland (Joint Project Leader,
7 3365 3428, email@example.com
Steve Phillipps, University of Bristol (Joint Project Leader, UK)
+44 (0)117 954 6881, email: s.phillipps@Bristol.ac.uk
Joss Bland-Hawthorn, Anglo-Australian Telescope
+61 2 9372 4251, email firstname.lastname@example.org
Warrick Couch, University of NSW (team member)
+61 2 9385 4578, email email@example.com
resolution image of the latest discovery, please contact UQ
library coordinator Diana Lilley, firstname.lastname@example.org,
+61 7 3365 2753.
resolution images can be seen at the following websites:
the new galaxies in the Fornax cluster.
page also includes other background information and images.
the Fornax cluster
Galaxy, the Milky Way, is at the centre of the map, at the
point marked “Local Group”.
ultra-compact dwarf might form.
numerical computation of the removal of the outer layers of
stars of a dE,N galaxy by tidal forces as it plunges past the central
galaxy NGC 1399. The insets show a `before and after' view of a normal
galaxy (top) and a UCD (bottom) as observed with the Hubble Space
CREDIT: UQ Communications. Insets: Hubble Space Telescope; background:
Curtis Schmidt Telescope and Arna Karick (University of Melbourne).
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