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The Question

(Submitted February 11, 1997)

Do any of your programs and/or archives address the X-ray/gamma-ray spectra of supernovae? Specifically, I am interested in determining the isotopic abundances that might be apparent in the effluvia surrounding supernovae and, especially, the one that occurred just a few years ago and was visible from, say, the observatory in Chile. Do you have any information and/or references that might be of value to me? Please note, again, that I am interested in isotopes, not elements. The latter would be apparent in visible spectra. Rather, I am interested in the relative abundances of the various isotopes.

The Answer

X-rays and gamma-rays can help us understand the isotopic abundances from supernovae. However, only for particular radioactive isotopes. Let me explain:

In a supernova explosion many elements and isotopes are created, mostly through the rapid process (r process). However, most of these are unstable so they decay down to a stable or more stable isotope. It is during this decay process that they give off gamma-rays. The energy of the gamma-ray will depend on the particular isotope and the process involved. These gamma-rays are observed as spectral lines within the overall spectrum.

Now a word about 1/2 life. The 1/2 life of a particular isotope is the time it takes for half of the initial quantity of the isotope to decay. So, observing a supernovae early on one can observe a number of these spectral lines, however over time they fade as there become fewer radioactive isotopes and more stable isotopes.

For example, the element Titanium 44 decays with a 1/2 life of about 70 years. The decay process gives off 1 MeV, 60 and 70 keV photons. By counting these photons, the mass of Ti 44 produced in the supernova explosion can be estimated.

Thank you for your question. As far as particular details of the supernova 1987A, I suggest that you do a literature search on this topic in the leading astronomical journals. This can be easily done online from the URL (

Jonathan Keohane
(for Imagine the Universe!)

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