Thursday, January 12, 2006

Cooling Flows

Continuing on with my day late and dollar short coverage of the AAS, I went to a session on "Cooling Flows in Galaxy Clusters" on Monday afternoon. It was very interesting. I had always been unsure of what goes on in clusters. I know there's alot of xrays there and radio emission, but it hasn't been something I've paid attention to. Also, with the cooling flows added to the mix, this session promised to be heavy on the hydrodynamics - never fun. But, I wanted to prove to myself that I was still a real astronomer, so I went.

A galaxy cluster is a big collection of galaxies (as you'd expect), and here is a picture of one. Kind of cool. Galaxy clusters are enormous, covering millions of light years, and can appear to be bigger on the sky than the moon. (We don't see them with our eyes because they're so far away and dim.) Because of all the mass present from all those galaxies, there is alot of energy. The central galaxy of a cluster is often a very large eliptical (here, I'm showing M87), that is usually an active galaxy (something like a quasar).

Even though we think of space as a vacuum, it really isn't. In between the galaxies of a cluster is a warm very low density gas called the "Inter-Cluster Medium" (ICM). This gas is heated up by the energy released by the central galaxy, and then tries to cool off by emitting radiation and moving away from the center of the cluster (much like the water in a kettle rises when it's boiling). We can see these cooling flows of gas when we observe the cluster in X-Rays. But, as you can see in the picture, the gas doesn't cool by moving spherically away from the center, it actually forms long filaments. The structure of these filaments is what the talks I saw was about, and it's actually pretty interesting.

Apparently, in the x-ray observations of the cluster, you can see bubbles being formed, where the density of gas is much lower. This is somewhat apparent in the above image, but might be a bit easier to see here. The structures in the gas are not well understood, and nor are the processes of the filaments. But, if you model the way that air bubbles rise through water, and what the water does underneath those bubbles, you find that it actually looks alot like these X-ray bubbles.

That's all I can say, since I don't know enough hydro to start giving you equations, but I find it pretty cool when processes on Earth resemble processes half-way across the universe. There is but one physics.

Here's a link to the session page. The abstracts are through the links in the paper titles. The last paper didn't actually happen in the session that I saw.

More later.


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