The red supergiant and supernova rate problems: implications for core-collapse supernova physics

Understand

Mapping supernovae to their progenitors is fundamental to understanding the collapse of massive stars.

• We investigate the red supergiant problem, which concerns why red supergiants with masses $\sim16$-$30 M_\odot$ have not been identified as progenitors of Type IIP supernovae, and the supernova rate problem, which concerns why the observed cosmic supernova rate is smaller than the observed cosmic star formation rate.
• We find key physics to solving these in the compactness parameter, which characterizes the density structure of the progenitor.
• If massive stars with compactness above $\xi_{2.5} \sim 0.2$ fail to produce canonical supernovae, (i) stars in the mass range $16$-$30 M_\odot$ populate an island of stars that have high $\xi_{2.5}$ and do not produce canonical supernovae, and (ii) the fraction of such stars is consistent with the missing fraction of supernovae relative to star formation.