Press Release

Hubble Finds “Backwards” Spiral Galaxy

By SpaceRef Editor
February 7, 2002
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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
by 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. A Hubble telescope photo of the oddball galaxy is this
month’s Hubble Heritage offering. The image shows NGC 4622 and its
outer pair of winding arms full of new stars [shown in blue].

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
has 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.

NGC 4622 is a rare example of a spiral galaxy with arms pointing in
opposite directions. What caused this galaxy to behave differently
from most galaxies? 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 core provides new
evidence for a merger between NGC 4622 and a smaller galaxy. This
information could be the key to understanding the unusual leading
arms.

Galaxies, which consist of stars, gas, and dust, rotate very slowly.
Our Sun, one of many stars in our Milky Way Galaxy, completes a
circuit around the Milky Way every 250 million years.

NGC 4622 resides 111 million light-years away in the constellation
Centaurus. The pictures were taken in May 2001 with Hubble’s Wide
Field Planetary Camera 2.

The science team, consisting of Ron Buta and Gene Byrd from the
University of Alabama, Tuscaloosa, and Tarsh Freeman of Bevill State
Community College in Alabama, observed NGC 4622 in ultraviolet,
infrared, and blue and green filters. Their composite image and
science findings were presented at the meeting of the American
Astronomical Society in January of 2002.

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)

EDITOR’S NOTE #1: For additional information, please contact
Dr. Ron Buta, University of Alabama, Dept. of Physics and Astronomy,
Box 870324, Tuscaloosa, AL 35487-0324, (phone) 205/348-3792, (e-mail)
buta@sarah.astr.ua.edu or

Dr. Gene Byrd, University of Alabama, Dept. of Physics and Astronomy,
Box 870324, Tuscaloosa, AL 35487-0324, (phone) 205/348-3793, (e-mail)
byrd@possum.astr.ua.edu or

Dr. Keith Noll, Hubble Heritage Team, Space Telescope Science
Institute, 3700 San Martin Drive, Baltimore, MD 21218, (phone)
410-338-1828, (fax) 410-338-4579, (e-mail) noll@stsci.edu.

Electronic images and additional information are available at:
http://heritage.stsci.edu and
http://oposite.stsci.edu/pubinfo/pr/2002/03 and via links in

http://oposite.stsci.edu/pubinfo/latest.html

http://oposite.stsci.edu/pubinfo/pictures.html

http://hubble.stsci.edu/go/news

EDITOR’S NOTE #2: “Picture-Perfect” Web Site Sheds Light on
Hubble’s Colorful Snapshots

Hubble Space Telescope’s beautiful and vividly colorful pictures of
galaxies, planets, and nebulae frequently invite the question “are those
colors real?” That question can now be answered by taking a look at the
making of Hubble images when visiting a new web offering from the Space
Telescope Science Institute’s popular “HubbleSite,” called “Behind The
Pictures.” The new site offers a tour of Hubble’s image factory – an
in-depth look at how the color pictures are actually constructed from
separate black and white photos. “Behind the Pictures” explains how
astronomers use color to enhance the scientific value of Hubble images
to more easily visualize celestial objects that ordinarily would be
invisible to the human eye.

For the full story, visit “Behind the Pictures” at
http://www.hubblesite.org/sci.d.tech/behind_the_pictures.

SpaceRef staff editor.