Astronomers discover nine new dwarf galaxies

Furthest discovery is a million light years away

The coloured and grey dots represent six of the nine newly discovered dwarf galaxies. Inset images show Eridanus 1(blue), Horologium 1 (red) and Pictoris 1 (yellow) (V. Belokurov, S. Koposov (IoA, Cambridge). Photo: Y. Beletsky (Carnegie Observatories))

Nine “dwarf galaxies” a million times smaller than normal galaxies have been identified in orbit around the Milky Way, in a discovery that could shed light on the mysterious dark matter of the Universe.

The mini galaxies are a billion times dimmer than the Milky Way and were only found with the help of the most powerful digital camera in the world, which can see the faint glow of normal-sized galaxies as far away as eight billion light years from Earth.

It is the biggest collection of dwarf galaxies observed at any one time, and the first in 10 years. Two teams of astronomers working independently discovered them in images taken of the southern sky during the search for the invisible dark matter that makes up a quarter of the total matter and energy of the Universe.

Dwarf galaxies contain about 5,000 stars, compared to the hundreds of billions of the Milky Way, which is why they give off so little light and are so difficult to detect. The closest of the nine is 95,000 light years away while the most distant is a million light years.

The dwarf galaxies were found near the large and the small Megallanic clouds, two of the most famous dwarf galaxies orbiting the much larger Milky Way, and were identified independently by scientists at Cambridge University and researchers at the US Fermi Laboratory in Batavia, Illinois.

“Dwarf satellites are the final frontier for testing our theories of dark matter. We need to find them to determine whether our cosmological picture makes sense,” said Vasily Belokurov of the Institute of Astronomy at Cambridge University.

“Finding such a large group of satellites near the Megallanic Clouds was surprising, though, as earlier surveys of the southern sky found very little, so we were not expecting to stumble on such a treasure,” Dr Belokurov said.

The Cambridge team said that three of the nine are definite dwarf galaxies, while the others could be either dwarf galaxies or globular clusters, containing stars and other cosmic objects that is not held together with dark matter.

Sergey Koposov of Cambridge said: “The discovery of so many satellites in such a small area of the sky was completely unexpected. I could not believe my eyes.”