Light Curve
Much of the "light curve," or graph of luminosity as a function of time after the explosion of SN 1987A, required radioactive decay processes to explain. Near the time of maximum luminosity, the spectrum contains lines of intermediate-mass elements from oxygen to calcium; these are the main constituents of the outer layers of the star. Months after the explosion, when the outer layers had expanded to the point of transparency, the spectrum was dominated by light emitted by material near the core of the star, heavy elements synthesized during the explosion; most prominently isotopes close to the mass of iron (or iron peak elements).
The radioactive decay of nickel-56 through cobalt-56 to iron-56 produced high-energy photons which dominated the energy output of the ejecta at intermediate (several weeks) to late times (several months). The peak of the light curve was caused by the decay of nickel-56 to cobalt-56 (half life 6 days) while the later light curve of SN 1987A in particular fit very closely with the 77.3 day half-life of cobalt-56 decaying to iron-56.
Read more about this topic: SN 1987A
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