A Rare Spiral in a Massive Cluster

Wow, this is one of those pretty pictures in astronomy that just draw you in. The more you look, the more you see. Obviously there’s a huge galaxy staring us in the face, looking as delicate as a jellyfish. But, the longer you look at the picture, the more galaxies you see. It’s astronomy’s version of the gift that keeps on giving.

The galaxy that takes up most of the field of view in this NASA/ESA Hubble Space Telescope image is NGC 4921. It lies about 320 million light-years away from Earth and is part of a giant conglomeration called the Coma Galaxy Cluster. As it turns out, NGC 4921 is a bit of a stranger in its own land. First, it’s spiral-shaped in a cluster where spirals are pretty rare, and second, it looks ghostly and pale and not quite like a “normal” spiral .

The Coma Cluster’s galaxies have been interacting for a long time, and as a result, many of the members have had their shapes sort of “smoothed out” into quiet ellipticals (meaning they are sort of oval-shaped, without spiral arms and without a lot of star formation that you see in active spirals). That makes spiral galaxies something of a rarity in the cluster.

If you look at NGC 4921 for a while you can see that there are kinda, sorta spiral arms in this galaxy, but they don’t seem as well-defined as those that make up our own Milky Way.  Those spiral arms are where new stars are being formed in the galaxy, but the star birth activity seems to have been dampened out, perhaps by past interactions. You can see a few bright blue young massive stars in the image, but otherwise there’s just a lot of dust swirling around — and, here’s the coolest part — peeking through that dust are galaxies of all shapes and sizes even farther away than this galaxy!  That’s something you don’t always get to see.

Spend some time with this picture — explore the large version when you click on the image. It will amaze and surprise you!