Variable star
A supernova may also result from mass transfer onto a white dwarf from a star companion in a double star system. The infalling matter pushes the white dwarf over the Chandrasekhar limit. The absolute luminosity of this type of supernova can be calculated from its light curve, so these explosions can be used to fix the distance to other galaxies. One of the most studied supernovae is SN 1987A in the Large Magellanic Cloud.