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Tuesday, May 15, 2007

Hubble spots giant ring of dark matter

By Colin Nickerson, Globe Staff

Scientists today reported a giant ring of ``dark matter'' detected by the international Hubble Space Telescope.

The ring lies 5 billion light-years from earth in a cluster of galaxies known only as ZwCl004+1652, the coordinates used to identify that region of the universe. The ring itself measures millions of miles across.

Dark matter, an invisible substance so ethereal it might be nothing except for its gravitational field, represents one of the great mysteries of astrophysics. Most astronomers and physicists are certain it is there -- the universe would have long since torn itself to tatters without its gravitational bonds -- but so far they can't prove it.

But discovery of the ghostly ring in a distant cluster of galaxies, announced by NASA and the European Space Agency, represents strong new evidence that the intangible substance not only exists, but pervades the cosmos.

The colossal ring, measuring 2.6-million light years across, was formed eons ago during a smash-up between two clusters of galaxies, scientists surmise.

The finding marks the first time that dark matter has been found in a formation all its own. Usually, dark matter has been conjectured by the force it exerts on surrounding ``real'' matter -- for example, galaxies and clouds of interstellar gas molded into otherwise inexplicable shapes by the gravitational pull of dark matter.

``This is the first time we've detected dark matter as having a unique structure that is different from the gas and galaxies in the cluster,'' said M. James Jee, an astronomer with Johns Hopkins University and a member of the US-European team that spotted the ring of dark matter.

``I was annoyed when I [first] saw the ring because I thought it was an artifact'' -- a false image -- ``which would have implied a flaw in our data reduction,'' he said. ``It took more than a year to convince myself the ring was real. I've looked at a number of clusters and haven't seen anything like this.''

Posted by Karen Weintraub at 01:27 PM
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