Stars with masses in the range 7 to 10 M end their liveseither as massive white dwarfs or weak type II supernovae, andthere are only limited observational constraints of either channel.Here we report
the detection of two white dwarfs with largephotospheric oxygen abundances, implying that they are bareoxygen-neon cores and that
they may have descended from themost massive progenitors that avoid core-collapse.
as the future solution to major societal problems such as sustainable energy (2). On page 980 of this issue, Lee et al. (3) use fluctuation electron microscopy to image subcritical nuclei in a solid material, observing metastable structural states that facilitate later nucleation in amorphous films. Their study is applied to a technologically important case of “phase-change memory” and therefore may facilitate efforts to design faster higher-density nonvolatile memory