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SYFY WIRE Bad Astronomy

A weird and lovely spiral for your weird and lovely Monday

By Phil Plait

I just got back from a week of travel, and I'm facing down a hundred emails, tons of news, about a billion things to write about, and then more travel later this week.

So when I see the folks at Hubble have posted a picture of a weird, pretty spiral, I figure it makes my job easier. I can just post a cool picture! So here it is:

[Click to galactinate.]

But dagnappit, I can't leave it at that. I never can.

This is NGC 4980, a spiral about 65 million light years away or so. Most spirals have well-defined arms, but this one is just... odd. The arms are indistinct, and also fairly asymmetric. If I had to guess I'd say it recently suffered a collision with another galaxy, but apparently there are no other galaxies near it! I was rather surprised to find that there isn't much in the professional literature about it; it's close and bright, and worthy of some study.

The arms of the galaxy are there, and appear blue from the combined light of billions of young, massive, hot stars. As with many spirals, there are older, redder stars in the center; those are in the arms as well, but outshone by the brighter blue stars. Usually, the cores of spiral galaxies long ago ceased making stars, so all the big blue ones have long-since exploded, leaving behind the cooler, redder stars.

Note that the very core of the galaxy is a pin-point source of light. I saw on some websites that NGC 4980 is an emission line galaxy -- it emits light at very specific colors, like a neon sign -- which is a clear indication that a supermassive black hole is gobbling down matter there in the galaxy's heart. As matter swirls in, it forms hot, flat disk (too small to see here) that is incredibly bright. This lights up clouds of nearby gas, which respond by glowing at those narrow slices of color. There aren't too many of these "active galaxies" near us on a cosmic scale, so again I'm rather surprised this hasn't been studied more!

So there you go. A lovely spiral to start your week, and one that's also a little bit on the odd side. Frankly, lovely and odd is how most of my weeks start, so I'm happy to share.

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