Galaxies grow and evolve over billions of years by absorbing nearby companions and merging with other galaxies. The early stages of this galaxy growth process are shown in a new image taken with the US Department of Energy’s (DOE) Dark Energy Camera (DECam) attached to the National Science Foundation’s (NSF) Víctor M. Blanco 4-meter Telescope at the Cerro Tololo Inter-American Observatory (CTIONS) program.
The massive barred spiral galaxy NGC 1532, also known as Halley’s Coronet, lies about 55 million light-years away in the direction of the southern constellation Eridanus (River). Its sweeping spiral arms are seen edge-on from Earth, with the proximal arm dipping downward and the receding arm thrusting upward, dragging it toward its small, dwarf companion galaxy, NGC 1531. These gravitationally bound galaxies will eventually merge completely into its smaller NGC 153 2companion.
Despite its small stature, the dwarf galaxy exerts a remarkable gravitational pull on its larger companion, distorting one of its spiral arms, which can be seen rising above the galactic plane. Also, plumes of gas and dust can be seen between the two galaxies, like a bridge of stellar matter held by competing tidal forces. This interaction caused star formation in both galaxies.
This lopsided cosmic tug of war is a snapshot of how large galaxies grow and evolve by swallowing smaller galaxies and absorbing their stars and star-forming material. A similar process may have occurred in the Milky Way Six times beforeLarge streams of stars and other signs remain in the Milky Way’s halo.
The process of absorbing a small companion galaxy is quite different from the catastrophic merger of two spiral galaxies of comparable size. In the latter case, two massive galaxies collide to form a completely different galaxy with its own shape and characteristics. This type of galactic merger will occur in the Milky Way when it merges with the Andromeda Galaxy four billion years later.
DECam, with its unparalleled wide-field imaging capabilities, provides astronomers with highly detailed views of these large-scale galactic interactions. It also has remarkable sensitivity, aided by the 4-meter Blanco telescope, needed to detect faint objects in our solar system and the influence of dark matter on galaxies across the visible universe. Currently, DECam is used for programs covering a wide variety of sciences.