Magazine article Science News

Galaxy Gets an Arm Extension: New Finding Suggests Milky Way Has a Rare Symmetry

Magazine article Science News

Galaxy Gets an Arm Extension: New Finding Suggests Milky Way Has a Rare Symmetry

Article excerpt

A new study suggests the Milky Way doesn't need a makeover: It's already just about perfect.

Astronomers base that assertion on their discovery of a vast section of a spiral, star-forming arm at the Milky Way's outskirts. The finding indicates that the galaxy is a rare beauty with an uncommon symmetry--one half of the Milky Way is essentially the mirror image of the other.

Thomas Dame and Patrick Thaddeus of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., say the structure they've discovered is most likely the outer extension of the Scutum-Centaurus arm from the inner galaxy. It appears that Scutum-Centaurus wraps all the way around the Milky Way, making it a symmetric counterpart to the galaxy's other major star-forming arm, Perseus.

The two arms seem to extend from opposite ends of the galaxy's central, bar-shaped cluster of stars, each winding around the galaxy, the researchers report in the June 10 Astrophysical Journal Letters.

Dame found evidence for the new structure while reviewing galactic data on atomic hydrogen gas, which radiates at a radio wavelength of 21 centimeters. After tracing the extension of the arm in the 21-centimeter radio emission, "I was in the unique position of being able to walk up two flights of stairs to the roof of my building [at Harvard] and search for carbon monoxide emissions from molecular clouds using the CfA 1.2-meter radio telescope," says Dame.

What he saw confirmed his initial finding. …

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