  The study of the stars that explode as supernovae used to be a forensic
study, working backwards from the remnants of the star. This changed in 1987
when the first progenitor star was identified in pre-explosion images.
Currently there are 8 detected progenitors with another 21 non-detections, for
which only a limit on the pre-explosion luminosity can be placed. This new
avenue of supernova research has led to many interesting conclusions, most
importantly that the progenitors of the most common supernovae, type IIP, are
red supergiants as theory has long predicted. However no progenitors have been
detected thus far for the hydrogen-free type Ib/c supernovae which, given the
expected progenitors, is an unlikely result. Also observations have begun to
show evidence that luminous blue variables, which are among the most massive
stars, may directly explode as supernovae. These results contradict current
stellar evolution theory. This suggests that we may need to update our
understanding.
