Nature's Particle Accelerator

Nature's Particle Accelerator
http://sciencenow.sciencemag.org/cgi/content/full/2006/1102/2

By Phil Berardelli
ScienceNOW Daily News
2 November 2006

Earthbound scientists reveling at the power of the forthcoming Large
Hadron Collider (LHC) in Switzerland might feel downright humbled by
what astronomers have discovered surrounding a distant cluster of
galaxies. An international team using the Very Large Array (VLA) radio
telescope in Socorro, New Mexico, has found giant, magnetic ringlike
structures that are propelling free electrons with millions of times
more energy than the LHC will be capable of producing. The discovery
sheds new light on how galaxy clusters form, and it might even solve
the mystery of the origins of high-energy cosmic rays.

Just as stars and planets begin as loose clouds of dust and gas, so too
do galaxies condense out of much larger agglomerations. As galaxies
move through space, their enormous gravity continues to drag along
these surrounding clouds. And when they collide or draw together in
clusters, they can compress and heat the clouds with an astounding
amount of energy.

Reporting in tomorrow's Science, the research team says it found "ring
segments" made of gigantic streams of magnetically charged particles
extending some 6 million light-years around a galaxy cluster called
Abell 3376, located more than 600 million light-years away. What's
surprising, says team leader Joydeep Bagchi of the Inter-University
Centre for Astronomy and Astrophysics in Pune, India, is that electrons
and other particles are whizzing inside the rings and behaving as
though they are being propelled by a giant linear accelerator, even
though they're located within an extremely low-density area of the
intergalactic medium. That suggests a tremendous source of energy has
created the rings--something powerful enough to keep the sun shining
for 20 trillion-trillion years. It's also enough to generate
high-energy cosmic rays' extremely powerful particles that bang into
detectors on Earth and have puzzled scientists for decades.

The most likely culprits, the team reports, are shock waves that formed
when the cluster's surrounding gas clouds slammed into each other at
speeds of thousands of kilometers per second. "Just as you hear a sonic
boom when shock waves from an airplane pass by you," says Bagchi, "we
believe that the situation in the Abell 3376 cluster is similar, with
ringlike radio structures tracing out the shock waves."

Still, the exact mechanism that produces the shock waves remains
unknown. Torsten Ensslin, of the Max Planck Institute for Astrophysics
in Garching, Germany, says there are two possible explanations. The
first is the head-on collisions of the galactic clouds. Or, he says,
the galaxies' gravity could be producing shock waves simply by pulling
any outlying matter closer to their centers. Ensslin, who has written
an accompanying commentary on the research, says in any case, "the
shock waves are sites of particle acceleration and candidate locations
for the generation of the still mysterious ultra-high energy cosmic
rays."