Date Time A Warp in Milky Way Linked to Galactic Collision When most of us picture the shape of the Milky Way, the galaxy that contains our own sun and hundreds of billions of other stars, we think of a central mass surrounded by a flat disc of stars that spiral around it. However, astronomers know that rather than being symmetrical, the disc structure is warped, more like the brim of a fedora, and that the warped edges are constantly moving around the outer rim of the galaxy. “If you have ever seen the audience making a wave in a stadium, it’s very similar to that concept,” said Xinlun Cheng, an astronomy graduate student in the University of Virginia’s College and Graduate School of Arts & Sciences. “Each member of the audience stands up and then sits down at the correct time and in the correct order to create the wave as it goes around the stadium. That’s exactly what stars in our galaxy are doing. Only in this case, as the wave is going around the galaxy’s disk, the galaxy disk is also rotating around the center of the galaxy. In terms of the sports-fan analogy, it’s as if the stadium itself is also rotating.”