The Local Group supernova rate.

From observations of distant spirals, a total of approximately six (H/50)-squared supernovas per century would be expected in Local Group galaxies other than the Milky Way. However, only one such object (S And) has been discovered during the last 100 years. The evidence available on historical galactic supernovas is roughly consistent with the supernova rate derived from distant spirals. It is thus tentatively concluded that the number of Local Group supernovas may have been unusually low during the last century or that some of them have unexpectedly remained undiscovered.