Rare Dwarf Galaxies Orbiting the Milky Way May Shed Light on Dark Matter

First Posted: Mar 11, 2015 06:35 AM EDT

Astronomers have discovered that we're not alone. They've found several rare dwarf satellite galaxies orbiting our own Milky Way. The findings could pave the way to better understanding dark matter, the mysterious substance that holds our galaxy together.

Dwarf galaxies in general were only first found in 2005. These small celestial objects orbit larger galaxies, and the new satellites were found in the southern hemisphere near the Large and Small Magellanic Cloud, which are the largest and most well-known dwarf galaxies in the Milky Way's orbit.

The newly discovered objects are about a billion times dimmer than the Milky Way, and a million times less massive. The closest one is about 95,000 light-years away and the most distant is about a million light-years away.

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

Standard cosmological models of the universe predict that there are hundreds of dwarf galaxies in orbit around the Milky Way. Yet their dimness and small size makes them difficult to find. This recent discovery, therefore, confirms these models. Not only that, but because dwarf galaxies contain up to 99 percent dark matter and just one percent observable matter, they're ideal for testing whether dark matter models are correct.

"Dwarf satellites are the final frontier for testing our theories of dark matter," said Vasily Belokurov, one of the study's co-authors. "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 a treasure."

The findings are published in The Astrophysical Journal.

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