There are a number of difficulties reconciling modelled and observed stellar evolution leading up to core collapse supernovae. Red supergiants are the progenitors for the vast majority of core collapse supernovae, and these have been observed but only at relatively low masses and luminosities, below about 18 M ☉ and 100,000 L ☉, respectively. Most progenitors of type II supernovae are not detected and must be considerably fainter, and presumably less massive. This discrepancy has been referred to as the red supergiant problem. It was first described in 2009 by Stephen Smartt, who also coined the term. After performing a volume-limited search for supernovae, Smartt et al. found the lower and upper mass limits for type II-P supernovae to form to be 8.5 +1 −1.5 M ☉ and 16.5 ± 1.5 M ☉, respectively. The former is consistent with the expected upper mass limits for white dwarf progenitors to form, but the latter is not consistent with massive star populations in the Local Group. The upper limit for red supergiants that produce a visible supernova explosion has been calculated at 19 +4 −2 M ☉.