A giant, fast-moving star creates a bow shock (the red arc) as it piles up gas and dust ahead of it. The star emits particles and radiation that compress matter as it moves through space. Because it is moving especially fast, the star compresses more material than most stars, creating the arc-shaped bow shock, which is like the water compressed in front of a boat. Astronomers are searching for more of these shock waves to help them locate fast stars, which may have been accelerated by gravitational encounters with other stars or by exploding companion stars. This image, which shows infrared wavelengths, was snapped by Spitzer Space Telescope. [NASA/JPL/University of Wyoming]