An object that seems to be an invisible galaxy made almost entirely of dark matter – the first ever detected – has been observed by a group of astronomers using the Lovell Telescope in England. The galaxy, which appears as a large amount of mass that rotates like a galaxy, could only be found using a radio telescope. The sighting was confirmed with the Arecibo telescope in Puerto Rico. The new dark galaxy has been named VIRGOHI21 and appears to be the first dark galaxy ever detected.
The astronomers, from the UK, France, Italy and Australia, have been studying the distribution of hydrogen atoms throughout the Universe. Hydrogen gas releases radiation that can be detected at radio wavelengths. In the Virgo cluster of galaxies they found a mass of hydrogen atoms a hundred million times the mass of the Sun. The Virgo cluster is a large group of galaxies about 50 million light years away. “From the speed it is spinning, we realized 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,” said Dr Robert Minchin from Cardiff.