Meet me at the bar!

“Oh, you hate your job? Why didn’t you say so? There’s a support group for that. It’s called EVERYBODY, and they meet at the bar.” –Drew Carey

When you think of a galaxy, you probably think of a bright, dense core with huge, swirling outstretched spiral arms. Something, perhaps, like the Silverado Galaxy, below.

And while there are many galaxies like this, it isn’t most of them! Oh, sure, most galaxies do have spiral arms, but they have something else, too. The Southern Pinwheel galaxy‘s got it,

the gorgeous NGC 1672‘s got it,

as does NGC 1300, which is directly face-on to us,

and some galaxies, like the Sculptor Galaxy, barely show it to us at all, but still have it. And you can see it, even though it’s nearly edge-on, if you look in the right light.

I’m talking, of course, about a bar! It turns out, of all the spiral galaxies we’ve ever discovered in the Universe, two out of three have bars!

Including ours!

(That’s not us; that’s the Great Barred Spiral Galaxy, which is about twice as big as us, but which looks a lot like we think we look.)

With a length of 27,000 light-years, the Milky Way’s bar extends more than halfway to the Sun’s position, and makes our galaxy even more common that we’d previously thought.

How do galaxies get bars, and what do these bars serve to do?

The center of the galaxy produces and sends out density waves, which become just slightly denser (by about 10-20%) than a typical place — without a density wave — in a galaxy.

The density waves attract gas and dust, and pre-existing stars! Furthermore, they provide a home for new stars to form, and studies even indicate that the bars funnel gas towards the core!

This could be bad for the gas, to get caught in the funnel created by the bar. Remember what we’ve got at the core of every galaxy?

A supermassive black hole! And if you remember what happens to matter falling into black holes, you’ll learn that this is one way to take a quiet, ordinary galaxy, and turn it into an active, jet-spewing engine!

This is really amazing, because when we look at galaxies a long time ago, when they were younger, we find that only 20% of them had bars, as opposed to 2 out of 3 today! So if you’ve got your heart set on going to the bar, remember that our galaxy’s already got one, and — as it’s probably pretty new — it’s no dive!

This are pretty recent discoveries, about how many galaxies have bars versus how many don’t (1999), about the bar in our own galaxy (2005), and about the fact that most younger ones didn’t have one (2007). So enjoy the new perspective on spiral galaxies, and when you see one without a bar, tell it to grow up, already!