Dani Maoz (Tel Aviv) gave a great talk today about the problem that (a) galaxy clusters contain enormous amounts of mass and enormous numbers of stars and are strongly gravitationally bound, and (b) they contain a large amount of iron (a few parts per thousand by mass), and yet (c) they show very low type Ia supernova rates. Either the supernovae go off very early in the lifetime of a stellar population, or else the metals are put out there some other way. The latter explanation—since there are no other ways of expelling metals into the intergalactic medium—is not plausible. But if the type Ia supernovae are prompt, there are issues in understanding supernova rates in the field. It is an extremely rich subject area that is only getting richer as supernova projects evolve, and Maoz is doing his statistics right.
ps: Maoz does most of his observing with a 1-meter telescope!
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