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Spiral Galaxy Spins the Wrong Way
Ant writes: "The New Scientist has an article about a galaxy in the constellation Centaurus is puzzling astronomers by spinning in the wrong direction. NGC 4622 has bright twisting arms containing newborn stars and lies 111 million light years away."
CNN has an article with more information.
You're continuing to misinterpret the article. The statement was that, for normal galaxies, the spiral arms trail the direction of rotation. That is, if the galaxy itself is rotating "clockwise", the spiral arms trail behind in a "counterclockwise" fashion.
However, in this case, the spiral arms lead in FRONT of the galaxy's rotation. That is, if the galaxy is rotating "clockwise", the arms stretch forward in the "clockwise" direction; if the galaxy is rotating ccw, the arms also stretch forward ccw!
The actual direction of rotation of the galaxy is irrelevant, the unexpected fact was the orientation of the spiral arms of the galaxy relative to the galaxy itself. Even in the event of an overlay, the rotation of the spiral arms in the unexpected direction could still be clearly observed.
In your given case, with two galaxies possessing "normal" behaviour, the arms on both galaxies would trail in the direction of the rotation. If they were spinning in opposite directions, then which arm belonged to which galaxy would be entirely evident through the direction in which the spiral arms were rotating.
Your objections, then, are entirely groundless.
But I suppose we can just blame the editors for the vague title.
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Floccinaucinihilipilification - the action or habit of judging something to be worthless
The Sun Newspaper Online has a worth and informative article about this discovery in its Science section.
I'm a bit confused at why anyone this that this is so bizzaire. Sure, most galaxies are trailing spirals, but there are enough leading spirals to make them not freakish. I'd suspect that it is the spin put on the story by the media, but one astronomer is quoted calling leading-arm spirals extremely rare.
My take on this is that the real news is the evidence of disruption/interaction. We've seen that before (M51, the Whirlpool, is a good example), but it's still a damned cool thing to see.
Says the math geek, I think this is as much of a mathematical problem as an astronomical one -- i.e., we really don't have a good grasp of the dynamics of galaxy formation, and we won't until the math is there. Classical Newtonian orbital mechanics doesn't do it, of course, since it's an n-body problem with a very, very large value of n. Some new kind of analytical technique needs to be invented before we can say we know much about why galaxies look and move the way they do.
The correlation between ignorance of statistics and using "correlation is not causation" as an argument is close to 1.
Here is a link to the guy's site--much more information and should be read before anybody starts making-up explanations.
There is a legitimate question here, and it's the subject of some tricky observing and analysis. You can get the Doppler map of the galaxy, by you need to work out which it is tipping towards you in order to work out if it is a leading or trailing arm spiral. It's hard to say if the "top" of the galaxy is nearer or us or the "bottom" is. If you can't tell that, you can't tell which way it is spinning.
The usual way of guessing at this it to look for globular clusters. The side that is nearer us will have fewer gobulars in front of it than the farther side. But this is a guess, of course. With a nearly face-on galaxy, this difference is harder to pick out.
You're right up until you state that the core must rotate more quickly. Dark matter has nothing to do with the core of the galaxy or its rotation. And even if the core did rotate rapidly, a la stars about a black hole, so what? There wouldn't be any radial mixing from that, as long as the orbits were Keplerian and nearly circular (which they are, as far as I've heard).
I also fail to see why this result indicates the presence of dark matter. The direction of rotation should not depend on the dark matter content. This is about how the galaxy formed and how the spiral arms were generated, not about what the galaxy is made of.