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."
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