Does the Milky Way really have a broken arm?

 Kind of!

While mapping the galaxy we discovered that there's a bunch of nebulas in the Sagittarius Arm that are kind of sticking out at an angle, like a broken bone poking through the skin (eww).

No, we don't know what exactly causes this, but we've seen it in other spiral galaxies (it's harder to map the one you're standing in).

It might well be caused by some kind of gravitational disruption. Perhaps a large, roaming black hole is the culprit?

Who knows, but it's kind of cool.