Why do the explosions of Type Ia supernovae have a more specific mix of elements and more predictable spectrum than those of regular Type II supernovae?
Type II supernovae are explosions of massive stars and the masses of these stars have a very wide range. On the other hand, Type Ia supernovae occur because of accretion onto a white dwarf and the explosion occurs when the mass of the white dwarf exceeds the Chandrasekhar mass (beyond which electron degeneracy pressure can no longer support the star). Hence Type Ia supernovae are explosions of stars with roughly the same mass. Hence, they look similar. If you could get a database of Type II supernovae of stars with same mass and metallicity (which is the amount of elements higher than Helium that the star has) then you might see similar spectra.
This page was last updated June 28, 2015.