Astronomers have found the edge of the Milky Way at last
Our galaxy spans 1.9 million light-years, a new study finds
In this image from the Fermi space telescope, the Milky Way's stellar disk, which runs horizontally along the middle, glows in gamma rays. A vast halo of dark matter engulfs the disk and emits no light at all, which makes measuring the galaxy’s total size a challenge.
Fermi LAT collaboration/DOE/NASA