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Radioactive ‘timers’ reveal likely source of galactic cosmic rays

22 April 2016 Astronomy Now

Most of the cosmic rays arriving at Earth from our galaxy come from nearby clusters of massive stars, according to new observations from NASA’s Advanced Composition Explorer (ACE) spacecraft. But the detection of a few radioactive cosmic-ray iron nuclei also indicates that there has been a supernova in our galactic neighbourhood within the last few million years.

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Chandra sees comets in the “X”-treme

18 April 2016 Astronomy Now

Scientists have determined that comets produce X-ray emission when particles in the solar wind strike the comet’s atmosphere. Recently, astronomers announced the results of a study using data collected with NASA’s Chandra X-ray Observatory of two comets — C/2012 S1 ISON and C/2011 S4 PanSTARRS — when both were relatively close to Earth.