Over billions of years, galaxies expand and change by absorbing close companions and merging with other galaxies. The early stages of this galactic growth process are showcased in a new image taken with the US Department of Energy’s (DOE) Dark Energy Camera (DECam) mounted on the National Science Foundation’s (NSF) Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory (CTIO), a Program of NSF’s NOIRLab.
About 55 million light-years away, in the direction of the southern constellation Eridanus (the river), is the huge barred spiral galaxy NGC 1532, sometimes referred to as Haley’s Coronet. Edge-on views from Earth reveal its sweeping spiral arms, with the closer arm sinking below and the farther arm lurching upward as it pulls on its smaller, dwarf partner galaxy NGC 1531. As NGC 1532 completely engulfs its smaller partner, these gravitationally connected galaxies will merge into one.
But despite its diminutive size, the dwarf galaxy has also been affecting its larger companion gravitationally, causing one of its spiral arms, which can be seen rising above the galactic plane, to be deformed.
Also visible between the two galaxies are plumes of gas and dust that resemble a bridge made of star matter that is held in place by opposing tidal forces. This interaction has also triggered bursts of star formation within both galaxies.
This cosmic tug-of-war between unbalanced forces is a representation of how big galaxies expand and change by consuming smaller galaxies and ingesting their stars and star-forming material. The Milky Way has likely undergone a similar procedure six times before, leaving behind massive streaks of stars and other traces in its halo.
As opposed to the catastrophic merging of two spiral galaxies of equivalent size, the process of absorbing a smaller companion galaxy is very different. In the latter case, two massive galaxies collide to form an entirely distinct galaxy with its own shape and characteristics. This type of galactic merger will happen to the Milky Way when it merges with the Andromeda Galaxy four billion years from now.
DECam, with its unparalleled wide-field imaging capabilities, gives astronomers highly detailed views of these large-scale galactic interactions. With the aid of the 4-meter Blanco telescope, it also possesses the exceptional sensitivity required to find dim objects in our solar system and study the effects of dark matter on galaxies throughout the visible universe. Currently, DECam is used for programs covering a wide range of science.
