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Milky Way has a 3,000-light-year-long splinter in its arm, and astronomers don’t know why

The Sagittarius arm of the Milky Way spirals out of our galaxy’s center, forming a swooping highway of gas that spans tens of thousands of light-years. This highway is dotted with the headlights of billions of stars, all seemingly moving along the same curvy track. But now, astronomers have found something unusual — a “break” in the arm, slashing perpendicularly through the spiral like a splinter poking through a piece of wood.

Spanning about 3,000 light-years, this stellar splinter makes up just a fraction of the Milky Way (which has a diameter of about 100,000 light-years). Still, the newfound break is the first major structure to be discovered disrupting the seemingly uniform flow of the galaxy’s Sagittarius arm, according to a study published online July 21 in the journal Astronomy and Astrophysics.

“This structure is a small piece of the Milky Way, but it could tell us something significant about the galaxy as a whole,” study co-author Robert Benjamin, an astrophysicist at the University of Wisconsin-Whitewater, said in a statement. “Ultimately, this is a reminder that there are many uncertainties about the large-scale structure of the Milky Way, and we need to look at the details if we want to understand that bigger picture.”

A contingent of stars and star-forming clouds was found jutting out from the Milky Way’s Sagittarius Arm. The inset shows the size of the structure and distance from the Sun. Each orange star shape indicates star-forming regions that may contain anywhere from dozens to thousands of stars. (Image credit: NASA)

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