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Monday, May 10, 1999 Published at 12:31 GMT 13:31 UK


Hubble nets a disaster

Chosen by voters - a 'polar-ring' galaxy

By BBC News Online Science Editor Dr David Whitehouse

It is what Net users wanted and Hubble duly obliged. Eight thousand Internet voters asked for the Hubble Space Telescope (HST) to take a close-up picture of the extraordinary "polar-ring" galaxy NGC 4650A.

Located about 130 million light-years away, NGC 4650A is one of only 100 known polar-ring galaxies. Their unusual disk-ring structure is not yet understood fully. One possibility is that the polar rings are the remnants of a galactic collision at least a billion years ago.

What is left of one galaxy became a rotating inner disk of old red stars. Meanwhile, the other galaxy which ventured too close was severely damaged or destroyed.

During the collision, which would have lasted tens of millions of years, the gas from the smaller galaxy would have been pulled away and captured by the larger galaxy, forming a new ring of dust, gas, and stars, which now orbit around the inner galaxy almost at right angles to the old disk.

Dark lanes

This HST image shows structures in the galaxy that were only recently discovered using large ground-based telescopes.

The image confirms that the bright, central concentration of light, which appears to be slightly orange in this image, has a completely smooth, regular appearance, indicating that it is a dense system composed of older stars.

The central dark lanes are due to the blockage of light by clouds of gas and dust in the ring.

The bright, bluish clumps, which are especially prominent in the outer parts of the ring, are regions containing luminous young stars, examples of stellar rebirth from the remnants of an ancient galactic disaster.

Visitors to the HST Website were asked to choose between three objects for an observation. Similar votes will be held in the future.

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