A stellar wind is the continuous outflow of gas from a star's surface into space. The Sun's version is mild, but massive hot stars drive winds so fierce they can shed several solar masses over their lifetimes, stripping away their outer layers before they explode. These winds carve bubbles in the surrounding interstellar medium, trigger star formation at the edges, and enrich the galaxy with the elements the star has made. How much mass a star loses this way largely decides whether it ends as a neutron star or a black hole.