We Have New Neighbours: Dwarf Galaxies Found Orbiting The Milky Way

By Chris Mills on at

Thanks to decades of work from scientists around the world (and the Hubble telescope's pretty pictures, of course), it feels like there's little left unknown in the universe. Which is probably why the casual discovery of, I don't know, nine new nearby galaxies came as something of a shock.

Using the results of the Dark Matter Survey, a team of astronomers from the University of Cambridge identified nine new dwarf satellite galaxies orbiting the Milky Way. Our new friends exist near the Large and Small Magellanic Cloud — the two largest and well-known of the dwarf galaxies.

"The discovery of so many satellites in such a small area of the sky was completely unexpected," said Dr Sergey Koposov, the study's lead author. "I could not believe my eyes."

We Have New Neighbours: Dwarf Galaxies Found Orbiting The Milky Way

The team is confident in the identity of three of the nine dwarf galaxies, but the remaining six could be either dwarf galaxies or globular clusters, which have similar visual properties to dwarf galaxies, but are not held together with dark matter. Follow-up spectroscopic analysis will be needed to determine which is the case.

The discovery is significant for more than just stargazing: the high dark matter content of the dwarf galaxies (around 99 per cent) make them ideal for testing our existing assumptions about dark matter and the way it behaves. According to Dr Vasily Belokurov, one of the study's co-authors:

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

The results were made possible thanks to the Dark Energy Survey, a five-year project using the Dark Energy Camera, a 570-megapixel camera mounted on the Victor M Blanco telescope in the Andes, in Chile. [Cambridge University]

Images: V. Belokurov, S. Koposov (IoA, Cambridge). Photo: Y. Beletsky (Carnegie Observatories) under Creative Commons