Solar system sits within a major spiral arm of the Milky Way

milky way

Our solar system lives in a major spiral arm of the Milky Way, a new study suggests. This view looking toward the center of the galaxy was taken at the ESO 3.6-meter telescope in the Chilean Atacama Desert.

S. Brunier/ESO

Our local galactic neighborhood might be more expansive than previously thought. Rather than being stuck in some backwater galactic community, our solar system lives along a major spiral arm of the Milky Way, researchers report online September 28 in Science Advances.

Astronomers suspected that our arm of the Milky Way — the Orion Arm — was just a bridge connecting two bands of stars and gas, the Sagittarius and Perseus spiral arms that wrap around the galaxy. Ye Xu, an astronomer at Purple Mountain Observatory in Nanjing, China, and colleagues measured distances to about two dozen stellar nurseries and found that they — and the sun — are scattered along an arm over 20,000 light-years long that parallels the two neighboring arms. This arc of a presumably larger spiral arm is comparable in length to what we can see of the Sagittarius and Perseus arms.

Despite being nestled inside the Milky Way, we know surprisingly little about it. Like trying to map a forest while standing among the trees, our view of the galaxy is limited, blocked by walls of interstellar gas and dust. Astronomers must infer the overall structure of the Milky Way through measurements like these and by comparisons to other nearby galaxies.

Star-forming regions (blue) trace out the Orion spiral arm where the sun (red circle) lives. Stellar nurseries along the neighboring Perseus and Sagittarius arms are shown in black and magenta; the center of the galaxy is marked with a red star. Y. Xu et al/Science Advances 2016

Christopher Crockett is an Associate News Editor. He was formerly the astronomy writer from 2014 to 2017, and he has a Ph.D. in astronomy from the University of California, Los Angeles.

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