The Milky Way Is Broken

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...