The Stars Beyond (Synopsis)

When you look out at the Universe, it comes as no surprise that it’s full of galaxies, each one with a dense, central collection of brilliant stars and an intricate structure all their own. They come in all sorts of structural varieties, with some in isolation, others in small groups, and still others in huge, massive clusters.

An SDSS image of elliptical galaxy NGC474 (center) and spiral galaxy NGC470 (right).
An SDSS image of elliptical galaxy NGC474 (center) and spiral galaxy NGC470 (right).

The bright galaxies we see are huge collections of billions of stars, with large intrinsic surface brightnesses. But surely there are components to these entities — less dense regions — that contain stars out hundreds of thousands of light-years beyond a galaxy’s typical edge. Until recently, this was only theoretical, but all of that is beginning to change.

The same pair of galaxies imaged to very low surface brightness with the MegaCam camera on CFHT. A complex and extended stellar halo consisting of stars of various ages (colors) is apparent. Image credit: Duc/Cuillandre/CFHT/Cole.
The same pair of galaxies imaged to very low surface brightness with the MegaCam camera on CFHT. A complex and extended stellar halo consisting of stars of various ages (colors) is apparent. Image credit: Duc/Cuillandre/CFHT/Cole.

Come read the whole story of the extended halos of stars around galaxies from James Bullock, and how they’re helping to shed light on galactic evolution!