Three years ago this blog reported on the low mass of the AD 1054 Crab Nebula semisupernova. (Unadjusted for the speed of light.) James Webb's telescope has looked in on the nebula 970 years thence that is, last week.
This has to do with the nickel:iron "Ni/Fe" ratio. The 2021 estimate pointed to Ni being high against Fe. It was concomitantly thought that the iron mass was too low for the classic "Type II" (=iron) core implosion. So they dug around for hypotheses as don't involve iron. They found a 1980 paper on "electron-capture". Q.E.D.!!
This ratio is now constrained better - in two regions anyway. Ni/Fe is indeed higher than, say, Sol. But not so high as to rule out Type II collapse.
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