Astronomers using the Dark Energy Camera (DEC) on NSF’s Víctor M. Blanco 4-m telescope at Cerro Tololo Inter-American Observatory, a Program of NSF’s NOIRLab, have obtained a spectacular image of the shell galaxy NGC 3923 with its symmetrical, onion-like layers.
NGC 3923 is located around 70 million light-years away in the constellation of Hydra.
Also known AM 1148-283, ESO 440-17, and LEDA 37061, the galaxy is 150,000 light-years across and has up to 42 faint shells.
“Galaxies can be divided into three main types: spiral, elliptical and irregular,” the NOIRLab astronomers said.
“Of these types, elliptical galaxies are the largest and are thought to evolve out of galactic collisions and mergers between spirals.”
“About one-tenth of elliptical galaxies are classified as shell galaxies, characterized by the concentric shells that make up their galactic halos.”
“A striking example of this type of galaxy is NGC 3923.”
NGC 3923 was discovered by the German-British astronomer William Herschel on March 7, 1791. Its shells were first spotted by the British-Australian astronomer David Malin in 1977.
“As is thought to be the story of all shell galaxies, the layered structure seen in NGC 3923 likely developed as a consequence of a merger with another, smaller spiral galaxy in the past,” the researchers said.
“As they merged, the larger galaxy’s gravitational field slowly peeled off stars from the smaller galaxy’s disk.”
“Those stars began to gradually mix with the larger galaxy’s outer halo, forming concentric bands, or shells.”
“A simple analogy is adding a drop of food color to a bowl of batter that you’re slowly stirring. The drop gets stretched out in a spiral that remains visible for a long time before completely mixing.”
“The shells of NGC 3923 make the galaxy quite exceptional,” they added.
“Not only does it have the largest known shell of all observed shell galaxies, but it also has the largest number of shells…
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