New Milky Way Tidal Stream in Triangulum
Stellar streams are found throughout the galactic halos of the Milky Way, Andromeda and other nearby massive galaxies. They are presumed to originate from disrupting dwarf galaxies or globular clusters, providing irrefutable evidence that galaxies are formed, at least in part, hierarchically. Furthermore, their orbits can be used to constrain the shape of galactic potentials at a range of distances. Most Galactic streams have been discovered in the Sloan Digital Sky Survey (SDSS), e.g. Monoceros stream, GD-1 and Orphan stream.
Image Credits: (header) NASA, ESA, J. Hester and A. Loll (Arizona State University)