Tiny Galaxy Sparkles in Our Back Yard

Contributed by
Dec 3, 2012, 12:14 PM EST

The diversity of nature constantly surprises me. If you asked me what the first thing I’d think of if you shouted the word “galaxy” at me, it would be something like the Milky Way: a large, disk-shaped pinwheel studded with stars, festooned with bright gas clouds, and splotched with dark dust clouds

Not all galaxies are like that, though. Some are puffy, some are elongated, some are just weird (technically, classified as “peculiar”). And then there’s ESO 318-38, a nearby galaxy that’s something of an underachiever when it comes to size, but that more than makes up for it in, well, glitteriness:

Not much is really known about this galaxy. I searched through the professional journals and found only one paper about it, where the astronomers examined 450 nearby galaxies to determine some of their basic physical characteristics (our friend here is listed as “P32250”, if you’re curious). In this case, we know it’s roughly 20 to 30 million light years away, and pretty small. Judging from its brightness it’s only about 1 percent or less the mass of our Milky Way, and as you can see by the picture, it’s mostly stars! There’s not a hint of gas or dust.

For a moment I was thrown by the stars being all blue, since only hot, young, massive stars are that color. That would be pretty weird, because stars are born from huge gas clouds, and there aren’t any that are obvious in this picture! But then I checked and saw that in this picture, what you see as blue is actually light from the orange/red part of the spectrum. In other words, this is false color. The astronomers used two filters to make this picture, one that lets through only orange/red light (shown as blue), and another that lets through only infrared light (shown as red). Those two colors are useful when you’re looking at stars, and they make for a pretty picture, but you have to be careful interpreting the picture!

So this looks to be an ordinary dwarf galaxy, fairly flat, and otherwise unremarkable except for its beauty.

If you grab the bigger version you’ll notice a couple of things. One is that there are lots of stars scattered across the field. Those are foreground stars, ones in our own galaxy. We’re inside the Milky Way, looking out at ESO 318-38, so nearby stars get in the way—think of it as looking out of a slightly dirty window at houses in the distance.

The other thing you’ll notice is that the picture is littered with lots of far more distant background galaxies. You can easily spot several dozen, many red and smudgy-looking. One, though, is a face-on spiral we can see right through ESO 318-38! That’s another indication our little friend is mostly stars and doesn’t have much gas and dust. If it did, then that more distant galaxy would be heavily obscured, but as it is we can see it pretty well. So this is like looking out a slightly dirty window to a distant house and seeing through its slightly dirty windows to a house even farther away. Except in this case looking isn’t rude or borderline illegal.

It never occurred to me before, but astronomy is the ultimate in voyeurism. We get to peek in on our neighbors, and it’s totally acceptable! In fact, I encourage it.

The metaphorical cosmic neighbors, I mean. Don’t take me too literally. And if you do, you’re on your own.