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.

2007 March 5
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Illusion and Evolution in Galaxy Cluster Abell 2667
Credit: NASA, ESA, Jean-Paul Kneib (Laboratoire d’Astrophysique de Marseille) et al.

Explanation: What's happening to the galaxies of cluster Abell 2667? On the upper left, a galaxy appears to be breaking up into small pieces, while on the far right, another galaxy appears to be stretched like taffy. To start, most of the yellowish objects in the above image from the Hubble Space Telescope are galactic members of a massive cluster of galaxies known as Abell 2667. The distortion of the galaxy on the upper left is real. As the galaxy plows through the intercluster medium, gas is stripped out and condenses to form bright new knots of stars. This detailed image of ram pressure stripping helps astronomers understand why so many galaxies today have so little gas. The distortion of the galaxy on the far right, however, is an illusion. This nearly normal galaxy is actually far behind the massive galaxy cluster. Light from this galaxy is gravitationally lensed by Abell 2667, appearing much like a distant person would appear through a wine glass. Each distorted galaxy gives important clues about how galaxies and clusters of galaxies evolve.

Tomorrow's picture: above saturn

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