Summary: 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.
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High resolution background image (tif 8Mb)
Caption: The Fornax Cluster of galaxies with insets, 60-times
magnified, of a normal dwarf galaxy (upper) and a newly-discovered
"ultra-compact dwarf" (UCD) galaxy (lower). A simulation of the
remains of a a normal dwarf galaxy after disruption to form a UCD is
shown in the centre.
Credits: Insets: Hubble Space Telescope; background Michigan Curtis Schmidt Telescope and Arna Karick (University of Melbourne).
Animation file (windows, 40MB, please contact Michael Drinkater for this file)
Credits: Dr. Kenji Bekki, University of New South Wales, Sydney
Credits: UQ Communications/European Southern Observatory (background)
The Hubble Space Telescope (NASA)
The Very Large Telescope (European Southern Observatory)
The 2.5-meter (100-inch) Irénée du Pont telescope at Las Campanas Observatory (Carnegie Institution of Washington)
The galaxies were originally discovered with the 3.9-metre Anglo-Australian Telescope.