Gaseous halo extends 1 million light-years from neighboring galaxy’s spiral disk
Adam Evans/Flickr (CC BY-NC 2.0)
The spiral disk of the Andromeda galaxy, the Milky Way’s neighbor, is just a tiny part of a much larger entity. The visible part of the galaxy is embedded in a tenuous halo of gas about six times as large as previously measured, researchers report in the May 10 Astrophysical Journal.
The halo is roughly 2 million light-years across — about 10 times as wide as the disk of stars — and extends nearly halfway to the Milky Way. If our galaxy has a similarly sized halo (which is tricky to measure for astronomers stuck inside the Milky Way), then the galaxies might be on the verge of touching (SN: 7/14/12, p. 10), says astrophysicist Nicolas Lehner of the University of Notre Dame in Indiana. Roughly 30 percent of Andromeda’s ordinary matter (excluding the