After a lengthy study of odd features in spiral galaxy thatlooks somewhat similar to our own, astronomers have decided that it rotatesbackward, or at least opposite from the expected direction based on its out-flungarms.

The galaxy, called NGC 4622, rotates clockwise, which wouldbe fine except that two outer arms point in that same direction. Outer arms ofspiral galaxies are made of stars, gas and dust, and they typically trail thegalaxy's rotational movement, their ends pointing in the opposite direction ofthe rotation.

The finding, made with a Hubble Space Telescope image, wasfirst presented in January at a meeting of the American Astronomical Society.But picking out the offbeat features was difficult for untrained eyes. Today,the image was re-released by the Hubble Heritage team at the Space TelescopeScience Institute, along with an illustration that illuminates the features.

Astronomers called the finding rare. The cause of the oddrotation is not known, but the galaxy may have consumed another, smallergalaxy, they say, which disturbed its structure. Such a merger is indicated bythe fact that the two outer arms are lopsided.

The science team consisted of Ron Buta and Gene Byrd fromthe University of Alabama, and Tarsh Freeman of Bevill State Community Collegein Alabama.

Byrd said he had first noticed the odd-looking arms in atextbook 15 years ago. He and Buta began in the early 1990s trying to determinewhich way the galaxy spun, a complex undertaking that involves figuring outwhich part of a galaxy is moving toward Earth and which part is receding. Itwas only when the researchers obtained the Hubble images that they knew forsure the galaxy spun backward in relation to two of the arms.

NGC 4622 is 111 million light-years away in the constellationCentaurus. The Hubble picture as taken in May 2001 with Hubble's Wide FieldPlanetary Camera 2. Blue objects in the image represent newly born stars.

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