Cosmic Rays ... Still Mysterious
Tuesday, June 3, 2008
Science Update - A look at CfA discoveries from recent journals

Cosmic rays are very rapidly moving nuclear particles that impact the earth from space, and generally originate from well beyond the solar system. The energies of these particles can be millions of times or more that of the most energetic particles produced in man-made particle accelerators. No one is sure where cosmic rays come from or how they are accelerated, but their influence can certainly be felt. On earth they can produce genetic mutations, or glitches in electronic systems, either directly or as they generate secondary particles in the atmosphere.

Astronomers for over fifty years have identified supernovae as tantalizing candidates for producing cosmic rays because the explosions generate extremely powerful shocks that can accelerate subatomic particles up to the humongous energies of cosmic rays. There is a lot of debate and disagreement about the specifics, however, and sometimes the scientific debate produces a negative result that is nearly as significant as a positive conclusion. In the case of cosmic rays, a recent controversy arose over conclusions drawn from X-ray flares from a supernova remnant that also produced very energetic gamma rays (both X-rays and gamma rays are forms of electromagnetic radiation, not particles, but they are produced when charged particles accelerate).

A paper last year argued, from details of the time-varying X-ray flux coming from one supernova remnant, that its gamma rays were actually produced by accelerating nuclear particles, and not by the more conventional electrons. The paper proposed that the supernova remnant had such strong magnetic fields that it was able to drive the motions of such nuclear particles, and argued that these flares could be the long-sought-after source of cosmic rays on earth. SAO astronomer Yousaf Butt, along with three of his colleagues, have now demonstrated that this analysis is wrong. Writing in the latest issue of the Monthly Notices of the Royal Astronomical Society Letters, the team shows that the behavior of the flares does not necessarily imply that nuclear particles are involved. Furthermore, they show that strong magnetic fields are incompatible with data from radio wavelengths, which would be a thousand times brighter if such fields existed. They conclude that the mysterious origins of cosmic rays are ... well, still mysterious.