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Cosmic Rays

29 December 2012

At http://phys.org/print275845800.html … cosmic rays are thought to originate in massive stars somewhere out in the universe, tiny particles that rain incessantly down from space. Victor Hess, around about a 100 years ago, established during a high altitude baloon flight that the radiation was cosmic in origin. Later, it was suggested the radiation might be gamma rays, an idea that has stuck. These are high energy electromagnetic radiation. Later, it was found the incoming rays were influenced by Earth's magnetic field implying they were charged particles. More recently, high altitude baloons were used once again and it was found the cosmic rays consisted of protons (hydrogen nuclei) and they were stripped down nuclei of heavier elements (also protons). Ninety per cent of cosmic rays are hydrogen nuclei, nine per cent helium nuclei, and just one per cent are of heavier elements. Since 1962 a handful of cosmic rays with high energies have also been spotted. These are so energetic scientists thought they might be powered by an extra galactic source such as a supermassive black hole. So, where do cosmic rays come from?

The answer is that science, as yet, has no definitive answer. Supernovas, it is thought, might be the culprit – the violent deaths of massive stars. In 1997 the ACE spacecraft showed some isotopes were more abundant in cosmic rays than in the solar system background – including the ratio of neo 20 to neon 22. It appears that the abundance of neon 22 was unexpected as it is produced by what are known as Wolf-Rayet stars, a stage in the evolution of big stars. During this time the stars shine extremely brightly – and appear to disperse a solar wind into the universe beyond. From this, it was deduced that both supernovas and the Wolf-Rayet of new stars contributed to cosmic ray production but the search is not finished as an updated version of ACE is about to be launched, in Antarctica, beneath the polar vortex.

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