Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

January 10, 1998

Disorder in Stephan's Quintet
Credit: W. C. Keel and R. E. White III (U. Alabama, Tuscaloosa), Kitt Peak 2.1-metre Telescope

Explanation: What are five closely grouped galaxies doing in this image? The grouping is commonly known as Stephan's Quintet. Four of the galaxies show essentially the same redshift suggesting that they are at the same distance from us. The large bluish spiral below and left of centre actually has a smaller redshift than the others, indicating it is much closer. It is probably a foreground object which happens to lie along the line of sight to the more distant galaxies. Of the four distant galaxies, three seem to be colliding, showing serious distortions due to gravitational tidal forces. The fourth is a normal appearing elliptical galaxy (at the lower right edge of the field). Recent results suggest that collisions play an important role in the life cycles of galaxies.

Tomorrow's picture: A Galaxy Cluster Lens

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