Back before the Hubble Space Telescope, before the Very Large Telescope, before ALMA, before digital cameras in general, folks did their best with smaller telescopes and chemically treated glass plates that acted like massive pieces of film. In these lower resolution images, weird mysteries were found and cataloged, and my personal favorite catalog is the Arp Atlas of peculiar galaxies. Astronomer Halton Arp used the Mount Wilson and Palomar observatories to image galaxies with unusual structures that ranged from splatter patterns of stars in colliding systems to things that are just a bit off.

One of these “just a bit off” galaxies is the egg-shaped spiral galaxy, Arp 79. 

In the more than fifty years since this catalog was published, researchers have been working to understand just how each of the systems in this catalog gets their weird shapes. New images of Arp 79 taken with the Gemini North telescope in Hawai’i reveal that, other than being very lopsided, like a lobster with one massive arm and one tiny one, this galaxy is otherwise a normal, dust-filled, star-forming spiral of a galaxy. 

The lopsided nature of this system is likely due to a smaller galaxy nearby pulling more on the one side and stretching out the one arm with its gravity. It doesn’t take a lot of mass to rearrange a spiral system, and one of the amazing things we’ve learned while looking at Arp’s Atlas is that almost every odd-shaped system out there has a companion galaxy that is making it look not quite right, and to understand the messy galaxy, we need to understand the companion that made it that way.

Put another way, no galaxy is weird in isolation; it takes a companion to help a galaxy get all bent out of shape. I’m going to try not to apply this lesson to anything beyond galaxies, but it does feel like there is a meme in here somewhere.

More Information

NOIRLab photo release