Quintessence of Dust

Every once in a while, I see a picture that simply stuns me. I have to say, this is one of them. A gorgeous Hubble image of NGC 7049, in the constellation of Indus. It’s also a Brightest Cluster Galaxy (imaginatively named because it’s… the brightest… in a cluster… of galaxies…), which typically means it must be old. Old and very massive.

This venerable giant is fascinating, at least to me, because of those spiralling dust lanes around its heart. So much so that it looks to be a bizarre hybrid between elliptical and spiral. Its shape certainly resembles a spiral, but there are no stars there in those spiral arms. Just dust.

Now I’m definitely no expert in galaxy evolution. I know full well that collisions between spirals tend to form giant ellipticals, but I’ve been told rather sternly before that ‘galaxies don’t evolve from ellipticals back to spirals’. In fact it’s popularly believed that star formation eventually shuts off in ellipticals. I’ve heard them informally referred to as ‘red and dead’, because they’re exactly that. They’re full of old red stars, with few or no new and blue ones being born. If I’m honest, this never sat well with me. A dead galaxy? How can something so massive die? What could quench star formation so much that an entire galaxy could fall derelict?

But this, at least to me, seems to resemble an elliptical galaxy which is evolving back into a spiral form. Which seems to make sense. If galaxies can indeed hide dark matter pancakes, then surely any interstellar gas and dust would be drawn to these. Collect enough gas and dust and you get giant molecular clouds. If you have giant molecular clouds, you can make stars.

Speculation, perhaps. I hope some passing galaxy head might take the time to pick out all of the flaws in my arguments. Though I think it’s probably safe to say that if we’re honest, no one understands galaxy evolution well enough to rule anything out.

In the meantime, I’ll just admire the prettiness of this picture. It’s rare to find something that actually tempts me to read more about galaxy evolution…

Image credits go to NASA, ESA, and W. Harris (McMaster University, Ontario).
A tip of the sombrero must go to His Badness, Phil Plait.
And no, this post has nothing to do with quintessence. The title’s a reference to Hamlet.

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
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