Chandra discovers relativistic pinball machine
Wed Nov 15, 2006 at 18:53 UTC
This extraordinarily deep Chandra image shows Cassiopeia A (Cas A, for short), the youngest supernova remnant in the Milky Way. New analysis shows that this supernova remnant acts like a relativistic pinball machine by accelerating electrons to enormous energies.
The blue, wispy arcs in the image show where the acceleration is taking place in an expanding shock wave generated by the explosion. The red and green regions show material from the destroyed star that has been heated to millions of degrees by the explosion.
Astronomers have used this data to make a map, for the first time, of the acceleration of electrons in a supernova remnant. Their analysis shows that the electrons are being accelerated to almost the maximum theoretical limit in some parts of Cas A. Protons and ions, which make up the bulk of cosmic rays, are expected to be accelerated in a similar way to the electrons. Therefore, this discovery provides strong evidence that supernova remnants are key sites for energizing cosmic rays.
Charged particles are believed to scatter or bounce off tangled magnetic fields in the shock wave, which act like bumpers in a pinball machine. When the particles cross the shock front they are accelerated, like they received a kick from a flipper in a pinball machine. Typically it should take a few hundred scatterings off the shock's magnetic field before the particles cross the shock front. It then takes about 200 crossings of the shock front to accelerate the particles seen in the Chandra data.
Image Credit: NASA/CXC/MIT/UMass Amherst/M.D.Stage et al.
Image Credit: NASA/CXC/MIT/UMass Amherst/M.D.Stage et al.
This figure shows regions in Cas A where the X-ray emission is generated by electrons spiraling along magnetic field lines and being accelerated as they pass across the remnant's shock front. In this acceleration map, the brighter parts of the image show where the acceleration is occurring relatively quickly. In the brightest areas the electrons are being accelerated almost as fast as theoretically possible.
Image Credit: NASA/CXC/MIT/UMass Amherst/M.D.Stage et al.
This image shows the temperature of the gas in the supernova remnant Cas A, assuming that the X-ray emission is caused by heat generated by the stellar explosion. Brighter regions represent higher temperatures. Although most of the remnant's X-ray emission is explained by heat from the explosion, in some regions the X-ray emission appears to be caused by a different mechanism. In the brightest regions of the image, corresponding to the blue regions in the 3-color image, energetic electrons spiral along magnetic field lines and are accelerated, generating X-rays that are detected by Chandra.
Scientists estimate it would take about 200 years -- over half the age of the remnant -- to accelerate electrons to cosmic ray energies in the slowest parts of the shocks, but only about 50 years to accelerate the highest energy electrons in the regions of maximum acceleration.
Chandra X-Ray Observatory News Release
