Massive star evolution: Luminous Blue Variables as unexpected Supernova
  progenitors
  Stars more massive than about 8 Msun end their lives as a Supernova (SN), an
event of fundamental importance Universe-wide. Theoretically, these stars have
been expected to be either at the red supergiant, blue supergiant, or
Wolf-Rayet stage before the explosion. We performed coupled stellar evolution
and atmospheric modeling of stars with initial masses between 20 Msun and 120
Msun. We found that the 20 Msun and 25 Msun rotating models, before exploding
as SN, have spectra that do not resemble any of the aforementioned classes of
massive stars. Rather, they have remarkable similarities with rare, unstable
massive stars known as Luminous Blue Variables (LBV). While observations show
that some SNe seem to have had LBVs as progenitors, no theoretical model had
yet predicted that a star could explode at this stage. Our models provide
theoretical support for relatively low-luminosity LBVs exploding as SN in the
framework of single stellar evolution. This is a significant shift in paradigm,
meaning that a fraction of LBVs could be the end stage of massive star
evolution, rather than a transitory evolutionary phase. We suggest that type
IIb SN could have LBV as progenitors, and a prime example could be SN 2008ax.
