Saturday, November 04, 2006

VIOLENCE ROCKS A CLUSTER

For the first time, an international team of astronomers has found observational evidence of shock waves and radio-emitting rings rippling around a giant galaxy cluster some 600 million light years away.

Observations made with the VLA (Very Large Array) radio telescope in New Mexico and with the European Space Agency's XMM-Newton x-ray observatory have confirmed the presence of both giant radio-emitting rings and magnetic shock waves around the galaxy cluster Abell 3376.

As reported in a recent issue of the journal Science, x-ray observations of Abell 3376 suggests that these emissions must have originated after the violent collision of smaller sub-clusters within the larger main cluster. These collisions are so powerful that researchers estimate that the resulting energy would be enough to keep our own sun alive and kicking for another 20 sextillion years. That's a 2 trailed by 22 zeroes.

Particle physicists and cosmologists alike are still puzzled over the origin of Ultra High Energy Cosmic Rays. Often the purview of science fiction, in reality, cosmic rays are highly-energetic atomic particles kicked up to speeds approaching that of light. While it's certain that the cluster Abell 3376 must be responsible for at least some cosmic rays, whether it is generating these ultra high energy rays is still open to debate.

Ultra High Energy Cosmic Rays --- some 100 million times more energetic than such particles created in the largest accelerators here on earth; have been detected by ground-based astronomers. But only future highly sensitive cosmic ray observatories will be able to determine if this far-flung galaxy cluster is the source of such ultra high energy particles. The bonafide origin of Ultra High Energy Cosmic Rays remains one of cosmology's greatest conundrums.

The above x-ray image from XMM-Newton shows a bullet-like supersonic
shock of x-rays emanating from gas superheated by
Abell 3376's sub-cluster collisions.

Image credit: Joydeep Bagchi, IUCAA, ESA

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