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News Release Archive:

News Release 161 of 291

February 7, 2002 12:00 AM (EST)

News Release Number: STScI-2002-03

Hubble Reveals "Backwards" Spiral Galaxy

A Hubble Heritage Release

February 7, 2002: Astronomers have found a spiral galaxy that may be spinning to the beat of a different cosmic drummer. To the surprise of astronomers, the galaxy, called NGC 4622, appears to be rotating in the opposite direction to what they expected. Pictures from NASA's Hubble Space Telescope helped astronomers determine that the galaxy may be spinning clockwise by showing which side of the galaxy is closer to Earth. This Hubble telescope photo of the oddball galaxy is presented by the Hubble Heritage team. The image shows NGC 4622 and its outer pair of winding arms full of new stars [shown in blue].

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Q & A: Understanding the Discovery

  1. 1. Why are astronomers surprised about the galaxy's clockwise rotation?


  2. Astronomers are puzzled by the clockwise rotation because of the direction the outer spiral arms are pointing. Most spiral galaxies have arms of gas and stars that trail behind as they turn. But this galaxy appears to have two "leading" outer arms that point toward the direction of the galaxy's clockwise rotation. To add to the conundrum, NGC 4622 also has a "trailing" inner arm that is wrapped around the galaxy in the opposite direction it is rotating. Based on galaxy simulations, a team of astronomers had expected that the galaxy was turning counterclockwise.

  3. 2. What may have caused the clockwise rotation and "leading" outer arms?


  4. Astronomers suspect that NGC 4622 interacted with another galaxy. Its two outer arms are lopsided, meaning that something disturbed it. The new Hubble image suggests that NGC 4622 consumed a small companion galaxy. The galaxy's two leading outer arms provide new evidence for a merger between NGC 4622 and a smaller galaxy.

 
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Image Credit: NASA and The Hubble Heritage Team (STScI/AURA)

Acknowledgment: Dr. Ron Buta (U. Alabama), Dr. Gene Byrd (U. Alabama) and Tarsh Freeman (Bevill State Community College)