Mike Irwin and the SDSS-II Collaboration

Beyond the shire.
This hobbit galaxy, known as Leo T, is too distant to be gravitationally bound to our Milky Way.

Hobbits in Space

SEATTLE, WASHINGTON--Astronomers have discovered a number of hitherto unknown "hobbit galaxies" meandering near our Milky Way. No, these diminutive star systems aren't stocked with small, furry-footed hominids, but their presence does confirm predictions that the formation of large galaxies left some crumbs on the table.

The galaxies--eight in all--were detected over the past several months by an international team of astronomers as part of the Sloan Digital Sky Survey, which has mapped about one fifth of the sky in unprecedented detail. The systems shine with the light of just a few thousand to about a hundred thousand suns, compared to hundred billion suns for our Milky Way galaxy. They're also small, measuring a couple thousand light years across (about one percent of the Milky Way's diameter), says team member Daniel Zucker of the University of Cambridge in the United Kingdom, who presented the discovery here today at the 209th meeting of the American Astronomical Society.

One intriguing hobbit galaxy, found only a few weeks ago, is called Leo T, after the constellation it was found in. Although it is only 1200 light years across and presumably has little gravity, radio observations show this diminutive galaxy still contains volatile gas from which new stars can form. Why star formation is still possible in Leo T, while the seven other hobbit galaxies are dead, is completely unclear. Another curiosity is Leo's lack of association with a major galaxy: it's 1.4 million light years away--too far to be gravitationally bound to our Milky Way galaxy.

The discovery of these tiny galaxies is welcome news, says cosmologist Marc Davis of the University of California at Berkeley. Computer simulations predict at least a hundred small satellites surrounding a big system like the Milky Way, he explains, but so far, only twelve satellite galaxies had been found, all of them substantially larger and brighter than the new population of hobbits.

Future sky surveys will probably show up many more of these inconspicuous systems. "I expect that there are dozens more to be found," says Zucker.

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