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Chandra illuminates origin of cosmic rays

New ultra-high detail images of Cassiopeia A from the Chandra X-Ray …

Credit: NASA/CXC/MIT/UMass Amherst/M.D.Stage et al.New data from the Chandra X-Ray observatory has offered up clues as to the origin of enigmatic high energy cosmic rays that bombard the Earth everyday.  By looking at the Milky Way's newest supernova remnant—the 325 year old Cassiopeia A remnant (pictured right, more images here)—astronomers have produced an acceleration map that shows the acceleration of charged particles that become cosmic rays.  This map shows that electrons are being sped up at near the maximum theoretical rate, lending experimental support and credence to the old theory that supernova remnants are a large source of these high energy cosmic rays.

In a process described as a relativistic game of pinball, charged particles bounce back and forth off the magnetic fields within the supernova remnant.  Each time they cross the shock front—the wispy blue lines at the outer edge of the remnant in the image—they are accelerated further.  As this process continues over time, the particles move faster and faster until they reach near light speeds.  Scientists working on the project say that particles will cross this shock front on average once for every 200 bounces, and that it takes about 200 shock front crossings for the particles to reach cosmic ray energy levels.  These numbers mean that Cassiopeia A started producing cosmic rays between 50 and 200 years after it exploded.

While cosmic rays consist of many types of rapidly moving, high energy particles—electrons, protons, and ions—only the electron's glow is visible as X-rays that Chandra could directly measure.  However, the research team theorized that all types of particles would undergo a similar pinball game, accelerating them to the high-energy velocities needed to obtain cosmic ray status.  In addition to gaining further understanding of the origin of cosmic rays, this data will help astronomers understand more about how these supernova remnants evolve and further our understanding of the original supernova explosion.

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Channel Ars Technica