Astronomical events that show brightness changes at optical wavelengths ranging froma thousandth of a magnitude to as much as twenty magnitudes over periods of a fractionof a second to years, are called optically variable events. Such events provide uniqueopportunity to study stellar properties, such as mass, radius, luminosity, temperature,internal and external structure, composition, and evolution.
Variable stars are classifiedas either extrinsic, wherein variability is caused by the eclipse of one star by another,the transit of an extrasolar planet or by the effects of stellar rotation (e.g. non sphericalstars), or intrinsic, wherein variability is caused by physical changes such as eruptionor pulsation in the star or stellar system (e.g. Supernovae, Active Galactic Nuclie,Cepheids).Supernovae are exploding stars, the very final stages of evolution for some stars,that releases tremendous energy.
All supernovae are produced via one of two differentexplosion mechanisms. The thermonuclear explosion of a white dwarf which has beenaccreting matter from a companion is known as a Type Ia Supernova, while the core-collapse of massive stars produce Type II, Type Ib and Type Ic supernovae. Supernovaeplay a key role in the synthesis of heavy elements and also signal the birth of neutronstars and black holes. These important and enigmatic astrophysical objects form fromthe cooling post supernova remnant and are the basic building blocks of other astrophys-ical systems such as pulsars and x-ray binaries. Supernovae produce and disseminatemost of the nuclei found in the Universe. Elements heavier than helium, through theiron group, are synthesized during the course of stellar evolution, and via supernovae,are disseminated into the interstellar medium to be reprocessed later in new stars, solarsystems, and other astrophysical systems. Supernovae have been of great physical sig-nificance as there are many physical processes involved, however many questions remainunanswered such as the various interconnections between different supernovae types, var-ious physical properties of different subclasses of supernovae. Furthure,it was assumedthat these Supernovae explosions are spherically symmetric.
Since we cannot spatiallyresolve the average extragalactic supernova, polarization is the most powerful tool whichallows to judge the shape of the ejecta.