Friday, 6 February 2009

Hubble captures exceptionally deep view of unusual spiral galaxy
Washington: A spectacular new image captured by the Hubble Space Telescope has revealed an exceptionally deep view of an unusual spiral galaxy.
The image of the galaxy, which is in the Coma Galaxy Cluster, has been created from data taken by the Advanced Camera for Surveys on the NASA/ESA Hubble S
pace Telescope.
It reveals fine details of the galaxy, NGC 4921, as well as an extraordinary rich background of more remote galaxies stretching back to the early Universe.
The Coma Galaxy Cluster, in the northern constellation of Coma Berenices, the hair of Queen Berenice, is one of the closest very rich collections of galaxies in the nearby Universe.
The cluster, also known as Abell 1656, is about 320 million light-years from Earth and contains more than 1000 members.
The galaxies in rich clusters undergo many interactions and mergers that tend to gradually turn gas-rich spirals into elliptical systems without much active star formation.
As a result, there are far more ellipticals and fewer spirals in the Coma Cluster than are found in quieter corners of the Universe.
NGC 4921 is one of the rare spirals in Coma, and a rather unusual one. It is an example of an "anaemic spiral", where the normal vigorous star formation that creates a spiral galaxy's familiar bright arms is much less intense.
As a result, there is just a delicate swirl of dust in a ring around the galaxy, accompanied by some bright young blue stars that are clearly separated out by Hubble's sharp vision.
Much of the pale spiral structure in the outer parts of the galaxy is unusually smooth and gives the whole galaxy the ghostly look of a vast translucent jellyfish.
The long exposure times and sharp vision of Hubble also allowed it to not just image NGC 4921 in exquisite detail, but also to see far beyond into the distant Universe.
This image was created from 50 separate exposures through a yellow filter and another 30 exposures through a near-infrared filter using the Wide Field Channel of the Advanced Camera for Surveys on Hubble.

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