Seeing The Invisible. First Dark Galaxy Discovered?

The ellipse shows the region of sky where the dark galaxy was found - image taken by Cardiff Astronomers using the Isaac Newton Telescope on La Palma.

A British-led team of astronomers using The University of Manchester's Lovell Telescope in Cheshire have discovered an object that appears to be an invisible galaxy made almost entirely of dark matter -- the first ever detected.

A dark galaxy is an area in the universe containing a large amount of mass that rotates like a galaxy, but contains no stars. Without any stars to give light, it could only be found using radio telescopes.

Following its initial detection at the Jodrell Bank Observatory, the sighting was confirmed with the Arecibo telescope in Puerto Rico. The unknown material that is thought to hold these galaxies together is known as `dark matter', but scientists still know very little about what that is.

The international team from the UK, France, Italy and Australia has been searching for dark galaxies using not visible light, but radio waves. In the Virgo cluster of galaxies, about 50 million light years away, they found a mass of hydrogen atoms a hundred million times the mass of the Sun.

Dr Robert Minchin from Cardiff University is one of the UK astronomers who discovered the mysterious galaxy, named VIRGOHI21, and explains: 'From the speed it is spinning, we realised that VIRGOHI21 was a thousand times more massive than could be accounted for by the observed hydrogen atoms alone. If it were an ordinary galaxy, then it should be quite bright and would be visible with a good amateur telescope. But, even using the large Isaac Newton Optical Telescope in La Palma, no trace of stars was seen ' it must thus contain matter that we cannot see ' so called dark matter.

Professor Andrew Lyne, Director of the Jodrell Bank Observatory, commented: 'We are delighted that the efforts by engineers at the Observatory and Cardiff University in building the Multi-Beam receiver system used for these observations had proved so fruitful. This exciting discovery shows that radio telescopes still have a very major role in helping to understand the Universe in which we live."

Further details, supporting images and contact details can be found at: http://www.jb.man.ac.uk/news/darkgalaxy/

Adapted from materials provided by University Of Manchester.

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