Space Swoon: This spiral galaxy is gorgeous, despite its short and stubby arms

Hey! Here’s a look at NGC 3981, which is gorgeous! Despite being short and stubby, cause hey. We’re all beautiful despite our flaws, right?

Bad Astronomy:

Hey! How about a gorgeous galaxy image for you today?

NGC 3981 is a lovely spiral at moderate inclination to us, giving us a spectacular view of its center and spiral arms. It’s roughly 80 million light years away (though I’ve seen some places saying it’s as close as 65 million; I base mine on its redshift which I plugged into Ned Wright’s Cosmology Calculator) and is part of a largish group of galaxies called the NGC 4038 Group, which includes the famous interacting Antennae Galaxies.

But that’s not really what I want to tell you about. Instead, take a look at the image: NGC 3981 is a little bit weird.

Don’t get me wrong. Holy wow, it’s beautiful! But it’s still weird. The spiral arms are all wonky. A lot of them are short and stubby, and, weirdly, straight. These short sections are called “rows”, and appear in many otherwise normal spiral galaxies. From a literature search, I don’t think it’s clear what causes them. Some authors have speculated that they are a large-scale phenomenon, working across thousands of light years in a galaxy, and may be due to shock waves created in gas clouds in the arms. But how this might create them isn’t known. That seems like a fruitful area of study for someone; interestingly I didn’t find any research papers focused on NGC 3981 at all; just its inclusion in some catalogs and such.

Overall, the structure of NGC 3981 is a bit messy, too, implying it may have suffered a collision with another galaxy sometime in the recent past. That makes sense if it’s part of a group of galaxies… but I didn’t find any galaxies very close to it in survey images. There’s a non-distinct elliptical not too far from it, but it looks too far and too small to have done the sort of damage seen in 3981. So I’m not sure what it’s doing.