A dust grain ejected when a massive star explodes as a supernova can follow a few different paths. One possibility is that it will leave its host galaxy entirely as part of a galactic wind. Nearly half of all grains in the Milky Way today may suffer this fate. Some of these grains will be destroyed in our galaxy’s hot halo and some will . . .Astronomy magazine subscribers can read the full answer for free. Just make sure you're registered with the website.