* Astronomy

Astronomers are puzzling over a spiral galaxy whose spiral arms are wrapped in opposing directions. The unusual structure may be a lingering scar from a tussle with a smaller galaxy that was ultimately swallowed.
Before astronomers had studied this unusual spiral galaxy, called NGC 4622, they thought the spiral arms of galaxies were always oriented the same way relative to the galaxy's direction of rotation. Specifically, spiral arms were always thought to follow, or trail, the direction of rotation the same way that a swirl of milk in a stirred cup of coffee naturally orients itself.
But in 2002, astronomers led by Ron Buta of the University of Alabama in Tuscaloosa, US, announced that NGC 4622, which lies 200 million light years away, was rotating the wrong way its prominent outer arms were leading instead of trailing. And one inner arm even appeared to be wound in the opposite direction from the outer arms.

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