The discovery of a pattern of X-ray “stripes” in the remains of an exploded star may provide the first direct evidence that a cosmic event can accelerate particles to energies a hundred times higher than achieved by the most powerful particle accelerator on Earth.
This result comes from a very long observation of the Tycho supernova remnant with NASA’s Chandra X-ray Observatory, operated for NASA by the Smithsonian Astrophysical Observatory. It could explain how some of the extremely energetic particles bombarding the Earth, called cosmic rays, are produced.
“We’ve seen lots of intriguing structures in supernova remnants, but we’ve never seen stripes before,” said Kristoffer Eriksen, a postdoctoral researcher at Rutgers University who led the study. This latest study from Chandra provides support for a theory about how magnetic fields can be dramatically amplified in such blast waves.
In this theory, the magnetic fields become highly tangled and the motions of the particles very turbulent near the expanding supernova shock wave at the front edge of the supernova remnant. High-energy charged particles can bounce back and forth across the shock wave repeatedly, gaining energy with each crossing. Theoretical models of the motion of the most energetic particles—which are mostly protons—are predicted to leave a messy network of holes and dense walls corresponding to weak and strong regions of magnetic fields, respectively.
The X-ray stripes discovered by the Chandra researchers are thought to be regions where the turbulence is greater and the magnetic fields more tangled than surrounding areas, and may be the walls predicted by the theory. Electrons become trapped in these regions and emit X-rays as they spiral around the magnetic field lines.
However, the regular and almost periodic pattern of the X-ray stripes was not predicted by the theory.
Assuming that the spacing between the X-ray stripes corresponds to the radius of the spiraling motion of the highest energy protons in the supernova remnant, the spacing corresponds to energies about 100 times higher than reached in the Large Hadron Collider. These energies equal the highest energies of cosmic rays thought to be produced in our Galaxy.
These results were published in the Feb. 20th, 2011 issue of The Astrophysical Journal Letters. Other co-authors include Carles Badenes from Tel-Aviv University and the Weizmann Institute of Science in Israel, Robert Fesen from Dartmouth College, Parviz Ghavamian from Space Telescope Science Institute, Baltimore, David Moffett, from Furman University, Greenville, S.C., Paul Plucinsky and Patrick Slane from the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass., Cara Rakowski from the Naval Research Laboratory, Washington, D.C., and Estela M. Reynoso from the Institute of Astronomy and Space Physics and University of Buenos Aires, Argentina.