Types of Supernovae

    Within the current models of supernova there are two main classifications. The basis for these classifications is the presence or absence of hydrogen emission lines in the spectra of the light emitted by the explosion. Type I supernova have no hydrogen spectral lines (Petschek, 1). One current model for type Ia supernova is a white dwarf pulling mass off of a giant companion star until it reaches the Chandrasekhar limit of 1.4 solar masses (Begelman & Rees, 32). The Chandasekhar limit was discovered by the Indian-American scientist Subrahmanyan Chandraesekhar, who did some of the first theoretical models of white dwarves(Kaufmann & Freedman, 546). At 1.4 solar masses the electron degeneracy forces cannot support the weight of the star, and it collapses (Kaufmann & Freedman, 558). Electron degeneracy is the point when electrons cannot be further compressed due to pressure drops ( Kaufmann & Freedman, 546). This model would account for the absence of hydrogen in a type Ia supernova’s spectra, because the star has already burned away most of its hydrogen during its main sequence life. Then shed the rest as it went from its red giant phase to a white dwarf.
    A type II supernova has the spectral lines for hydrogen (Petschek, 1). Type II explosions are thought to be very massive single stars that produce an iron core of 1.4 solar masses. The core is layered through a chain of thermonuclear reactions during the expansions and contractions in its giant or supergiant phase. The hydrogen spectral lines are produced by the hydrogen in the outer layers of the star as they are excited by the huge amounts of energy released by the breakdown of all the fused atoms in the core (Kaufmann & Freedman, 558).
      There are still many inconsistencies in the classification of supernovae. Some type I explosions start to show hydrogen in their spectra later in the explosion, i.e.. supernova 1993J (Murdin article, 668) The classification of supernovae is still in its infancy and much remains to be explained. For our purposes we will focus on type II explosions since they are less complex than binary models and better understood.