EMBARGOED UNTIL PUBLISHED IN NATURE (May 29 2003, 4am AEST) (MAY BE RELEASED FOR PREVIEW 1 WEEK IN ADVANCE, BUT NO STORIES TO BE PUBLISHED BEFORE EMBARGO DATE) Scientists confirm presence of new class of galaxy A major international research effort has discovered a new type of very small galaxy, known as an "ultra-compact dwarf galaxy" (UCD). The galaxies are so compact that astronomers previously mistook them for nearby stars in galaxy censuses based on large, ground-based pictures taken of the sky. The finding, reported today in Nature, was made by a team of eight astrophysicists from Australia, the U.S., Germany, and the U.K. Project team leader, UQ Senior Lecturer in Physics Dr Michael Drinkwater, said the discovery confirms a suspicion that has been troubling astronomers for over 25 years. "There has always been the concern that galaxy surveys are biased against finding very diffuse galaxies, because they are so faint, and very compact galaxies, because they look just like stars", he said. "Obviously, it is very important that we have a complete inventory of all galaxy types if we want to have an accurate knowledge of how much luminous (and even dark) matter is in the universe, as well as understand all the ways in which galaxies are formed." Dr Drinkwater said the researchers found the ultra-compact dwarf galaxies while observing all objects in the direction of the Fornax Cluster - a bound system of about 300 galaxies which is 60 million light years away. Professor Couch (UNSW) notes that The Fornax Cluster is, relatively speaking, at our doorstep. Even so, it is still difficult to tell whether galaxies in its direction appear small because they are actually so, or because they are just so far away, at distances well beyond the cluster. "Our Fornax Cluster Survey addressed this problem by using innovative technology to measure the distances to some 3,500 objects in the direction of the cluster." The UCDs were first discovered with the 3.9m Anglo-Australian Telescope (AAT) at Siding Spring Observatory, Coonabarabran. Dr Drinkwater said this challenging task was made possible with the AAT's Two Degree Field Spectrograph (2dF), which can measure 400 objects simultaneously. Amongst the 2500 objects that had previously been identified as stars, 7 were actually found to be members of the Fornax cluster. At this distance they were too bright to be stars, but rather had to be a new class of extremely compact `dwarf' galaxy, which had never been seen before. The researchers then won rare time on the Hubble Space Telescope to measure how big these dwarf galaxies were, as well as time on the European Southern Observatory's Very Large Telescope in Chile to measure how fast stars are moving around inside these galaxies. These two measurements are used in combination by astronomers to "weigh" galaxies and find out how massive they are. This confirmed the UCDs to be a new type of low-mass galaxy held together by gravity. Dr Drinkwater believes that these new galaxies can help test theories as to how galaxies in large groups like the Fornax Cluster are transformed and even destroyed. Team members were Dr Michael Drinkwater of The University of Queensland; Dr Michael Gregg of the University of California at Davis, and the Lawrence Livermore National Laboratory in California; Dr Michael Hilker of Bonn University; Dr Kenji Bekki and Professor Warrick Couch of the University of New South Wales; Dr Harry Ferguson of the Space Telescope Science Institute in Baltimore; Dr Bryn Jones of the University of Nottingham; and Dr Steven Phillipps of the University of Bristol. The work has received Australian Research Council funding of $180,000 for a two-year program Media: Further information, Dr Michael Drinkwater telephone: 07 3365 3428 email: mjd@physics.uq.edu.au Sydney contact: Professor Warrick Couch telephone: 02 9385 4578 email: wjc@bat.phys.unsw.edu.au