A Gossamer Galaxy – NGC 4921

There are jewels in the night sky and some of them are more fanciful than others. The spiral galaxy NGC 4921 is a case in point. Please click on the following links in the article for much higher resolution images. (Click for a larger image.)

NGC 4921 Image Courtesy of Hubble/ESA

This beautiful barred-spiral galaxy resembles more a ghostly cosmic jelly fish than the typical spiral galaxy you may think of like the Whirlpool galaxy (M101) below:

Whirlpool Galaxy - Image Courtesy of Adam Block, Mt. Lemmon SkyCenter, U Arizona

You’ll notice immediately that NGC 4921 is missing the well defined spiral arms seen in the Whirlpool. There is structure there, but it is much more subtle.  You do see a dark swirl of dust around the core, accented with bright blue stars that are forming along this band.  And, you can see the bar that extends across the nucleus of the galaxy as well as some spiral structure to the arms.

To me, what is most remarkable about this galaxy is that the white gossamer cloud is not dust but stars – billions and billions of unresolved stars spread very uniformly around the galaxy.  In a well defined spiral galaxy we don’t get the same impression of the vast number of stars contained within because they are clumped together in the arms.  NGC 4921 and the Whirlpool galaxies are roughly the same size (about 200,000 lightyears verses 175,000 lightyears across), so comparing the two galaxies gives a good sense of how many stars are condensed into the arms.  It is interesting that this type of galaxy is termed an “anaemic spiral” because of the uniform distribution of stars.

The galaxy is located about 320 million lightyears away in the galaxy cluster known as the Coma Cluster or alternatively Abell 1656 in the constellation Coma Berenices.  If you look closely at the image you will see thousands of galaxies scattered about NGC 4921 and even behind the nebulous galaxy.  Some are part of the Coma Cluster, while others extend much further beyond it.  This annotated image below (Click for a larger image.) shows highlights some of the details contained in this amazing image.

NGC 4921 Annotated Image Courtesy of Hubble/ESA

     Check out the Hubble website for more information, images and several short videos that will give you more in-depth information about this beautiful jewel of the night sky.   Enjoy the wonders of the Cosmos!

Till next time,

RC Davison

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