The Stars Beyond
"Each galaxy has a story. Some are small but growing rapidly. Others look bland but betray a complex, vibrant past. What’s more, most large galaxies — again like some cities — appear to be built upon the ruins of smaller, more ancient ones. Our home galaxy, the Milky Way, is not unlike Rome in this respect. Ancient stellar remains show up viscerally in the the faint, extended outer reaches of galaxies — regions of light so diffuse that they’ve been difficult to study until recently."
You’ve no doubt heard of dark matter halos around galaxies: vast, extended, spherical collection of mass that reach for hundreds of thousands of light-years beyond what we typically think of as a spiral or elliptical galaxy. But did you know that galaxies contain vast, extended stellar halos as well? Moreover, they look nothing like you’d expect! They’re not spherical or even ellipsoidal, but highly irregular, and have an awful lot to teach us about how galaxies came to be the way they are today. Galaxy evolution expert James Bullock has the story.