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Steve Roy
Media Relations Dept.
Marshall Space Flight Center, Huntsville, AL
steve.roy{at}msfc.nasa.gov
(256) 544-0034

Megan Watzke
Chandra X-ray Obs. Center, CfA, Cambridge, MA
cxcpress{at}cfa.harvard.edu
(617) 496-7998

For release: 05-08-03

Photo release no.: 03-074

Stephan's Quintet: Intruder galaxy shocks tightly knit group
http://www1.msfc.nasa.gov/NEWSROOM/news/photos/2003/photos03-074.html

The hurly-burly interactions in the compact group of galaxies known
as Stephan's Quintet are shown in the upper left where a Chandra
X-ray Observatory image, in blue, is superimposed on a Digitized Sky
Survey optical image, in yellow. Shock-heated gas, visible only with
an X-ray telescope, appears as a bright blue cloud oriented
vertically in the middle of the image and has a temperature of about
6 million degrees Celsius. The heating is produced by the rapid
motion of a spiral galaxy intruder located immediately to the right
of the shock wave in the center of the image, as shown in the galaxy
labeled B in the wide field optical image on the lower right.

Stephan's Quintet is an excellent example of the tumultuous dynamics
of a compact group. The motion of the galaxies through the hot gas,
and the gravitational pull of nearby galaxies are stripping cool gas
from the galaxies, thereby depriving them of the raw material from
which to form new stars. In a few billion years the spiral galaxies
in Stephan's Quintet will likely be transformed into elliptical
galaxies. 

During the past few billion years additional gas may have been
stripped from the galaxies in the group and heated by collisions such
as the one seen in these images. An intruder that may have passed
through the center of the group at least twice is the faint galaxy C
seen in the wide field optical image. The fainter blue cloud in the
X-ray/optical image may be a relic of past collisions.

The four galaxies A, B, D and E strung out diagonally across the wide 
field optical image are at a distance of about 280 million light
years from Earth. The large-appearing galaxy F in the lower left of
this image has now been identified as a foreground galaxy at a
distance of about 35 million light years, leaving the group
originally identified as Stephan's Quintet with only a quartet of
galaxies. However, if we include galaxy C, which is at the same
distance as the other four galaxies, it becomes a quintet again!

Ginevra Trinchieri of the INAF-Brera Observatory in Milan, Italy,
Jack Sulentic of the University of Alabama in Tuscaloosa, and Dieter
Brietschwerdt and Wolfgang Pietsch of the Max-Planck Institute for 
Extraterrestrial Physics in Garching, Germany are co-authors of a
paper that describes the Chandra data on Stephan's Quintet. The paper
will appear in an upcoming issue of the journal Astronomy &
Astrophysics. 

NASA's Marshall Space Flight Center in Huntsville, Ala., manages the 
Chandra program.

Credits:
X-ray: NASA/CXC/INAF-Brera/G.Trinchieri et al.
Optical: Pal.Obs. DSS

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