Stars forming in small groups within dense and dusty stellar nurseries.
A galaxy is a gravitationally bound system that contains stars, stellar remnants, gas, and dust. This luminous matter is embedded in significantly larger amounts of dark matter, a telltale sign of a galaxy, as opposed to a large star cluster containing no dark matter. There are spiral galaxies such as the Milky Way, old elliptical galaxies that form from long merged galaxies, and currently merging irregular ones. The Andromeda galaxy is the Milky Way’s sister galaxy and is 2.5 million light years away. Both are gravitationally bound and on collision course. All galaxies in the universe form a giant web-like structure.
Spiral galaxy UGC 2885, located 232 million light-years away in the northern constellation Perseus. The galaxy is 2.5 times wider than our Milky Way and contains 10 times as many stars. A number of foreground stars in our Milky Way can be seen in the image, identified by their diffraction spikes. The brightest star photobombs the galaxy's disk. The galaxy has been nicknamed "Rubin's galaxy," after astronomer Vera Rubin (1928 – 2016), who studied the galaxy's rotation rate in search of dark matter. Credit: NASA, ESA and B. Holwerda (University of Louisville)
Over 1.5 million of the brightest stars and galaxies in the nearby universe, detected by the Two Micron All Sky Survey (2MASS) in infrared light. Across the center are stars that lie in the plane of our own Milky Way Galaxy. Away from the Galactic plane, the vast majority of the dots are galaxies, color coded to indicate distance, with blue dots representing the nearest galaxies in the 2Mass survey, and red dots indicating distant galaxies. Named structures are annotated. Many galaxies are gravitationally bound to form clusters, which themselves are loosely bound into superclusters, which in turn are sometimes seen to align over even larger scale structures.
Photo Credit: 2MASS, T. H. Jarrett, J. Carpenter, & R. Hurt