Cartwheel galaxy

I think what I like most about this image isn't the high technology involved in combining images of the same structure from 4 different telescopes, nor even the deep insights into the physics of galactic collisions that it provides. What I like most about the picture is all the pretty colours.

More specifically, I'm fascinated by what it means that this picture is so colourful. What it does mean is that there within this galaxy there are regions of space where qualitively different things are going on. There's got to be at least 7 or 8 different colours in that picture. Each of these colours represents a region of space with a particular distribution of dust and gas and stars of various different sizes. All the different colours mean that there are lots of different such distributions. In some places, space is mostly full of dust and gas. In others, there are stars which are mostly very old. In others, there are stars which mostly very young. Why different areas of space have such different characteristics is a mystery to me - that's why I find the different colours so fascinating.

Here's another fascinating picture. This isn't a painting, an artist's impression or a computer graphic, it's a photograph (albeit a very high-tech one) taken by the Hubble Space Telescope. If you had a sufficiently powerful telescope and pointed it in the right direction, that's exactly what you'd see. It's really hard to get a sense of the incredible scale of this galaxy from the picture, but it's about 50,000 light years across. That means even the finest details you can see in the dust rings surrounding the galaxy are each hundreds of light years across. This thing is just unimaginably big, yet the size of these fine details compared to the size of the whole thing makes it look like something on a much more familiar scale. One would expect something that big to be quite smooth but that isn't the case.

It seems that the universe has a great deal of structure at all scales, like a fractal.

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