Sunday, November 05, 2006
A Galaxy Like a Tossed Pizza Crust and Other Amazing Things
Most galaxies are spiral --either plain spiral or spiral barred--(the other categories are elliptical or strange) but nearly all of them are flat, seen edge on, except this one, ESO 510-G13. This warpage is from interaction with another galaxy (not in the picture). Our Galaxy seen in Earth's night sky (when you can see it) takes up about a third of the sky. A planet in the unfashionable west end of an outer spiral arm of that galaxy would have the galactic plane of stars (a milky way) take up the entire night sky.
But that's nothing compared to another common galactic feature, the globular cluster of stars. To the left is one of the 147 such clusters in our galaxy, M80 (NGC 6093), with hundreds of thousands of relatively close packed stars. Imagine the night sky of a planet in the center, which night sky would be nearly as bright as day here. Isaac Asimov used that idea as the central physical feature of his story Nightfall; stay away from the horrible film of the same name.
In space there is the repeated physical feature of aggregations of stars and planets, like in solar systems, star clusters and galaxies, surrounded by a lot of empty space. Just so, as there are cluster of stars, there are, here and there, (an amazing, even mind blowing concept) clusters of galaxies, like the one below, Abell 2218.
While somebody needs to be right on the equator, the odds are against any particular star being that close. Basically, it's just a bit too convenient, and that's always suspicious
Either the observations are correct and it's just one of those things, or the observations are incorrect. If they're incorrect, that has implications for many other things as well. Perhaps there are dust clouds that we aren't seeing (affecting other observations and mass estimations), perhaps we can't estimate distances as well as we think we can (with all the attendant follow-on effects), or perhaps it's something we haven't even thought of.
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