Archive for December 23rd, 2011

December 23, 2011

Cosmic rays from stellar superbubbles

Cosmic rays were discovered almost 100 years ago (1912), yet astrophysicists are still uncertain about where they come from or how they acquire their extremely high energies. Research recently published gives strong evidence that the Cygnus X region, which contains hundreds of very hot, massive, young stars, is a source of cosmic rays and has the means to accelerate them to high energy.

A great deal is known about cosmic rays. They are not electromagnetic radiation (such as gamma rays) but instead consist of charged particles of ordinary matter – electrons, protons, or other atomic nuclei. Of nuclei heavier than hydrogen or helium, the elements represented in cosmic rays occur in proportions close to, but not quite the same as, what is found in typical interstellar gas. A few heavier elements are overrepresented.

The amount of kinetic energy carried by most cosmic rays can range up 1000 TeV (1015 eV), but a small number may be up to 1021 eV. The energy of the highest energy cosmic rays exceeds what could be produced by any known source within our galaxy, so the source is unknown, but likely to be a very energetic active galaxy.

Since cosmic rays are charged particles, their trajectories are bent and twisted by galactic magnetic fields, so there’s no direct way to identify their place of origin by the direction from which they arrive. Possible sources have to be examined individually to determine their ability to produce cosmic rays. For lower energy cosmic rays (under 1000 TeV) the possible sources inside our galaxy include supernova remnants and clusters of very hot, young stars. The new research gives evidence for one instance of the latter.

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