Galaxies so small they're called "hobbits"
www.chinaview.cn 2007-01-19 21:33:18

    BEIJING, Jan. 19 (Xinhuanet) -- Scientists familiar with "The Lord of the Rings" have coined a name for a new class of ultra-faint galaxies in Earth's Local Group of galaxies: "hobbit."

    The Local Group is a collection of about 40 galaxies, dominated by the Milky Way and Andromeda. The rest are mostly small satellites known as "dwarf galaxies" that are gravitationally bound to these two galaxies. The Large and Small Magellanic Clouds are two of the Milky Way's better known dwarf galaxies.

    A recent sky survey revealed eight new members in our Local Group of galaxies, including the "hobbit" galaxies and what might be the smallest galaxy ever discovered.

    "They seem to be much fainter than anyone suspected galaxies could be before," said study team member Daniel Zucker of Cambridge University. "So rather than dwarf galaxies, we should perhaps call them ‘hobbit galaxies.'"

    The new galaxies were detected during the past two years as part of the Sloan Digital Sky Survey (SDSS-II) and presented last week at the 209th meeting of the American Astronomical Society in Seattle.

    Seven of the new galaxies are gravitationally bound to the Milky Way, while the eighth appears to float freely in space.

    The new Local Group members are even smaller and fainter than other known dwarf galaxies, with luminosities ranging from only a thousand to at most a few hundred thousand times that of our sun.

    The dimness could be the result of stellar age, as seven of the new galaxies contain mostly old stars. Of these seven, two are located in the constellation Canes Venatici, one in Bootes, one in Leo, one in Coma Berenices, one in Ursa Major and one in Hercules.

    The eighth and most recently spotted galaxy is in many ways the most interesting. Titled Leo T, it is about 1.4 million light-years away from Earth, so far away that it floats freely in space, unperturbed by the Milky Way.

    Unlike the other hobbit galaxies, Leo T includes both old and young stars. It also has large amounts of neutral hydrogen gas -- a prime ingredient of star formation -- suggesting it is still an active birthing ground.

    Because of its great distance, Leo T is also the dimmest of the new hobbits.

    "This is basically the smallest, faintest star-forming galaxy known, by orders of magnitude," Zucker explained.

    Current galaxy formation theories predict our Milky Way should be surrounded by a swarm of smaller satellite galaxies. But until the new survey, only 12 had been identified. Astronomers have named this issue the "missing satellite problem."

    The new galaxies could go a long way toward solving this problem and might represent just the tip of a cosmic iceberg, the researchers say.

    "The Sloan Digital Sky Survey covers only a fifth of the night sky, so there must be many more dwarfs out there," said study team member Wyn Evans, also of Cambridge University.

    And more hobbits?

    (Agencies)

Editor: Gareth Dodd
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