Rare dwarf galaxies found orbiting the Milky Way

Chuck Bednar for redOrbit.com – @BednarChuck

The Milky Way appears to have some new next-door neighbors, as astronomers from the University of Cambridge have found a “treasure trove” of nine previously undetected dwarf satellites (including three small galaxies) in orbit around the galaxy we call home.

According to the researchers, the findings come from newly released imaging data taken from the Dark Energy Survey and represent the largest number of dwarf satellites ever discovered at one time. The discovery could help scientists learn more about dark matter, the mysterious and invisible substance that comprises much of the universe and holds the Milky Way together.

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The satellites are located in the southern hemisphere in the area around the Large and Small Magellanic Cloud, the largest dwarf galaxies orbiting the Milky Way, and are detailed in a new study published by The Astrophysical Journal.

In addition to the three confirmed dwarf galaxies, the Cambridge-led team found six objects that could be either dwarf galaxies or globular clusters, according to CNET. Globular clusters are not held together by dark matter, but dwarf galaxies are believed to be up to 99 percent comprised of the mysterious substance, making them ideal for testing dark matter models, the website noted.

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Dwarf galaxies are the also smallest galaxy structures observed, and the faintest one contains a mere 5,000 stars. In comparison, the Milky Way contains hundreds of billions of stars. Standard cosmological models of the universe predict that there are hundreds of these dwarf galaxies in orbit around the Milky Way, but since they are so dim and small, they are extremely hard to find.

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

The final frontier

“Dwarf satellites are the final frontier for testing our theories of dark matter,” added co-author Dr. Vasily Belokurov, also from the Institute of Astronomy. “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.”

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The closest of the newly discovered objects is located approximately 97,000 light years away in the constellation Reticulum, about halfway to the Magellanic Clouds. Due to the massive tidal forces exerted by the Milky Way, it is currently in the process of being ripped apart.

The most distant one is located right on the outer fringe of the Milky Way, 1.2 million light years away in the constellation of Eridanus, and the study authors report that it may be home to a small globular cluster of stars. If so, it would be the faintest galaxy ever found to contain one.

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“These results are very puzzling,” noted co-author Wyn Evans, also from 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.”

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Source: http://www.redorbit.com/news/space/1113351353/rare-dwarf-galaxies-found-orbiting-the-milky-way-031215/