Peanuts in the Sky

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For nearly a decade, radio astronomers have recorded the telltale signals emitted by a streamer of hydrogen clouds off the far edge of the Milky Way. Most scientists have believed that the source of the signals is somewhere in the giant galaxy of some 200 billion stars that includes the sun and its planets. But a University of Maryland astronomer has a different idea. S. Christian Simonson III concludes in Astrophysical Journal Letters that the source is a separate pint-size galaxy—the Milky Way's closest cosmic companion.

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Most galaxies have been discovered by conventional optical telescopes. Earth's new galactic neighbor was "discovered" in the classroom. Simonson had been puzzling over the hydrogen clouds' radio signals for several years. But it was during a recent lecture that the message came through. Simonson knew that frequency shifts in the radio signals from one of the clouds indicated that one side of the cloud was approaching the earth while the other was moving away. Suddenly he realized why. Such movement could only mean the presence of a great rotating mass. Said Simonson: "I knew right then in the classroom that it had to be a galaxy."

Simonson now hopes to aim an optical telescope at the rotating hydrogen cloud that is the core of the galaxy in an attempt to spot some of the 200 million stars that he estimates it contains; he will use those sightings to determine the galaxy's distance from earth. If the existence of the little galaxy is confirmed, it may be given a name. Until then, the hydrogen cloud will be known officially as 0627—15 (for its position in the sky). But the suspected galaxy, which has only one one-thousandth the mass of the Milky Way, has already been given a simpler nickname. Simonson's colleagues have decided to call it "Snickers," after the candy bar, because compared to the Milky Way, it is "only peanuts."

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