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Thursday, March 2, 2000

This is the Chandra X-ray Observatory image of the
galaxy cluster Abell 2142. The image shows a "colossal
cosmic weather system" produced by the collision of two
giant clusters of galaxies, according to astronomers from
the University of Hawaii and other institutions. Abell 2142
is 6 million light years across and contains hundreds of
galaxies and enough gas to make a thousand more. It is
one of the most massive objects in the universe.

Scientists ID
intergalactic cold front

UH experts help with
what NASA calls a colossal
cosmic weather system

By Helen Altonn


University of Hawaii University of Hawaii and other astronomers studying images from NASA's Chandra X-ray Observatory have identified an "intergalactic cold front" created by the collision of two giant clusters of galaxies.

The clash of galaxies produced what NASA calls a "colossal cosmic weather system."

The first detailed look at the system's pressure fronts show a central region of 50 million degrees - relatively cool compared with the surrounding environment.

The bright central area is embedded in a large elongated gas cloud of 70 million degrees and both "are rolling in a faint 'atmosphere' of 100-million-degree gas," NASA reported.

"One of the remarkable things is ... you just can't go to a laboratory and create an experiment to check out what's going on in these things," said Doug Burke, post-doctoral fellow in the Hawaii Institute for Astronomy's Chandra Science Center.

Burke's responsibilities involve testing and developing software to analyze data from Chandra. "So it's actually very nice to be able to use the software I've been testing on real data and get interesting results," he said.

Maxim Markevitch of the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass., compared the gigantic weather system to an intergalactic cold front. "A major difference is that in this case, cold means 70 million degrees," said the leader of the international team analyzing the observations.

"These objects are so large that you have to think about them in different scales ... " Burke said. "The features we see are over 100,000 light years across - these fronts we see in the X-ray image."

The X-ray Observatory has been exploring the cosmos only a few months, operated from the Marshall Space Flight Center in Huntsville, Ala. Besides colliding galaxies, it can see exploding stars, black holes and other high-energy cosmic objects.

"This is like progressive work," Burke said. "This relatively short observation with Chandra is so very encouraging, we can see features, in effect, in a snapshot. I think it bodes well that we can see so much detail even with our first look at these objects with the instrument.

The gas clouds imaged by Chandra are in the core of a galaxy cluster called Abell 2142. It is 6 million light years across and contains hundreds of galaxies and enough gas to make a thousand more, NASA said, adding that it is one of the most massive objects in the universe.

Galaxy clusters collide and merge over billions of years, growing to huge sizes as smaller clusters are pulled inward by gravity. Tremendous amounts of energy are released, heating the cluster gas to 100 million degrees.

The late stages of the merger process are shown in detail for the first time in the Chandra images, NASA said.

Scientists previously had used the German-U.S. Roentgen satellite to produce a broad picture of the cluster. The elongated shape of the bright cloud suggested two clouds were in the process of becoming one, but details weren't clear.

Chandra is capable of measuring variations of temperature, density and pressure with unprecedented detail, NASA said.

The observations were made Aug. 20 with Chandra's Advanced CCD Imaging Spectrometer.

Burke joined the UH Chandra Science Institute, headed by astronomer J. Patrick Henry, in mid-June. He was previously at the John Moores University in Liverpool, England.

The results will be published in the Astrophysical Journal.

University of Hawaii
Ka Leo O Hawaii

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