  We present a novel mechanism to enhance the mass-loss rates of massive stars
shortly before their explosion. The neutrino luminosities of the stellar core
of massive stars become larger as they get closer to the time of the core
collapse. As emitted neutrinos escape freely from the core, the core mass is
significantly reduced when the neutrino luminosity is large. If a star is near
the Eddington luminosity when the neutrino luminosity is large, the star can
exceed the Eddington luminosity because of the core neutrino mass loss. We
suggest that the stellar surface mass-loss rates due to the core neutrino
emission can be higher than 1e-4 Msun/yr from ~ 1 year before the core
collapse. The mass-loss rates can exceed 1e-2 Msun/yr in ~ 10 days before the
core collapse. This mass-loss mechanism may be able to explain the enhanced
mass loss observed in some supernova progenitors shortly before their
explosion. Even if the star is not close enough to the Eddington luminosity to
enhance mass loss, the star can still expand because of the reduced
gravitational force. This mechanism can be activated in Wolf-Rayet stars and it
can make hydrogen-poor, as well as hydrogen-rich, dense circumstellar media
observed in some supernovae.
