Andromeda Galaxy in History

A faint dwarf spheroidal companion designated Andromeda I is identified as part of the growing satellite system surrounding M31.

The dwarf spheroidal galaxy Andromeda II is recognized as another satellite member of the M31 system.

Andromeda III is identified as a faint dwarf spheroidal companion, expanding the known population of galaxies gravitationally associated with M31.

NASA's Chandra X-ray Observatory obtains a deep view of the M31 nucleus and surrounding X-ray sources, including emission near the central black hole position.

Chandra results reveal numerous X-ray binaries in the central region of M31 and isolate an X-ray source consistent with the position of its supermassive black hole.

NASA releases a highly sensitive ultraviolet mosaic of M31 from GALEX, tracing young hot stars and recent star formation across its disk.

Spitzer records thousands of infrared exposures of M31, mapping warm dust and star-forming structures that are difficult to isolate in visible light.

Spitzer infrared imaging shows an asymmetric ring of star formation and a gap in Andromeda's disk, suggesting past interactions with satellite galaxies.

Infrared measurements from Spitzer are used to estimate the mass of Andromeda's stars and to characterize the distribution of its old stellar population.

A combined ultraviolet and infrared view separates hot young stellar populations from cool dusty star-forming regions across M31.

A merger-history study proposes that M31 experienced a dominant collision with a large galaxy about two billion years ago and links the event to its stellar halo and M32.