Nine new dwarf galaxies found orbiting Milky Way

A team of astronomers from the University of Cambridge have identified nine new dwarf galaxies orbiting the Milky Way, the largest number ever discovered at once, according to a Cambridge statement. The new satellites were found in the southern hemisphere near the Large and Small Magellanic Cloud, the largest and most well-known dwarf galaxies in the Milky Way's orbit.

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

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

According to the Cambridge team, three of the discovered objects are definite dwarf galaxies, while others could be either dwarf galaxies or globular clusters - objects with similar visible properties to dwarf galaxies, but not held together with dark matter.

Dwarf galaxies are the smallest galaxy structures observed, the faintest of which contain just 5000 stars. The Milky Way, in contrast, contains hundreds of billions of stars. Standard cosmological models of the universe predict the existence of hundreds of dwarf galaxies in orbit around the Milky Way, but their dimness and small size makes them incredibly difficult to find, even in our own 'backyard'.

Since they contain up to 99 percent dark matter and just one percent observable matter, dwarf galaxies are ideal for testing whether existing dark matter models are correct. Dark matter - which makes up 25 percent of all matter and energy in our universe - is invisible, and only makes its presence known through its gravitational pull.

"Dwarf satellites are the final frontier for testing our theories of dark matter," said Dr Vasily Belokurov of the Institute of Astronomy, 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 treasure."

"These results are very puzzling," said co-author Wyn Evans, also of the Institute of Astronomy. "Perhaps they were once satellites that orbited the Magellanic Clouds and have been thrown out by the interaction of the Small and Large Magellanic Cloud. Perhaps they were once part of a gigantic group of galaxies that - along with the Magellanic Clouds - are falling into our Milky Way galaxy."

The Cambridge research, funded by the European Research Council, will be published in the Astrophysical Journal.

http://timesofindia.indiatimes.com/followceleb.cms?alias=University of Cambridge,Milky Way Galaxy,milky way,Dwarf galaxies,Astrophysical Journal

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