Anne’s Image of the Day: Spiral Galaxy NGC 4921

April 28, 2014

NGC 4921, a barred spiral galaxy in Coma Berenices

Image Credit: NASA / ESA / Roberto Colombari / Hubble Legacy Archive

NGC 4921 (also known as UGC 8134) is a barred spiral galaxy, located about 320 million light-years away from Earth in the northern constellation of Coma Berenices (Berenice’s Hair), while it is speeding away from us at approximately 5,482 kilometers per second. It lies near the center of the Coma Cluster, a large cluster of galaxies that contains over 1,000 galaxies.

Visible in the galaxy are, from the center, a nucleus with a bright bar that is surrounded by a prominent ring of dark dust. Then a band that contains blue clusters of recently formed stars. The outer part consists of unusually smooth, poorly distinguished spiral arms. Surrounding the galaxy are several smaller companion galaxies, many unrelated galaxies in the far distant universe, and unrelated stars in our own Milky Way Galaxy.

This galaxy is categorized as an anemic galaxy because of its low rate of star formation, its remarkably diffuse spiral arms and low surface brightness. Nonetheless, it is the brightest spiral galaxy in the Coma Cluster.

NGC 4921 is low in non-ionized hydrogen gas. The distribution of the gas has also been deeply perturbed toward the south-east spiral arm and is less extended than the optical disk of the galaxy. This may have been caused by interaction with the intergalactic medium, which is stripping off the gas. This ram stripping, as it’s called, is common with spiral galaxies in dense clusters; as they move through the cluster environment.

On May 4, 1959, a supernova explosion, called SN 1959b, was observed in this galaxy. It reached an estimated peak magnitude of 18.5.

This image is taken with the Hubble Space Telescope.