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The Question
(Submitted October 30, 2003)
Are some cosmic rays nuclei of iron atoms, and are they from sources in our
own galaxy? I read that the ultrahigh-energy cosmic rays that arrive to our
atmosphere at 1020 electron volts (eV) or more, are mainly protons?
Have any cosmic rays nuclei of iron ever been detected at this range of energy?
The Answer
Thank you for your question. The cosmic rays that have been identified
as iron are believed to originate from supernova explosion shock waves
in our galaxy.
We don't yet know the composition of the ultra high energy cosmic
rays, since they are not directly detected. Although protons seem the
likeliest candidate, there is no real physical evidence to support
this.
For more on cosmic rays, see
http://helios.gsfc.nasa.gov/cosmic.html.
-- Michael Loewenstein and Amy Fredericks
for "Ask a High-Energy Astronomer"
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