Enter the Dark Galaxy

"Astronomers have discovered an object that appears to be an invisible galaxy made almost entirely of dark matter. The team, led by Cardiff University in Wales, claims it is the first such object to be detected.

"Very little is known about 'dark matter,' even though there is much more of it in the cosmos than the 'normal,' or baryonic, matter that constitutes the visible material from which stars and planets are built. Astronomers say the discovery marks an important breakthrough because, according to cosmological models, dark matter is five times more abundant than the baryonic matter.

"We only know of dark matter's existence because of its influence on ordinary matter. Scientists can infer its presence by looking at the rotation of galaxies and measuring how fast their visible components are moving.

"Astronomers have seen galaxies where the material is moving so fast that they should fly apart -- as they don't, there must be a stronger gravitational force acting than can be accounted for using visible matter."


The ellipse in the left image shows the region of space where the dark galaxy (VIRGOHI21) was found. The right image shows the type of galaxy that astronomers would have expected to see, based on the measurements taken.

"In the Virgo cluster of galaxies, the research team found a mass of hydrogen atoms a hundred million times the mass of the Sun. Dr Robert Minchin of Cardiff University said: 'From its speed, 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.'"


From the Cardiff research team:

"Without any stars to give light, VIRGOHI21 could only be found using radio telescopes. It was first seen with the University of Manchester's Lovell Telescope in Cheshire, and 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.

"Dr. Jon Davies, one of the team of astronomers from Cardiff University, says; 'The Universe has all sorts of secrets still to reveal to us, but this shows that we are beginning to understand how to look at it in the right way. It's a really exciting discovery!'


See also:
Ghostly galaxy: Massive, dark cloud intrigues scientists
First invisible galaxy discovered in cosmology breakthrough
Dark matter clouds may float through Earth