Type 1a supernovae are used as standard candles in the luminosity/ distance scale of the universe, the assumption being that they form from a known configuration of progenitors, a late-type red giant, and a white dwarf companion, (single degenerate...SD..) or two degenerate types (double degenerate...DD..).
The authors write a seventh paper in a series, investigating about 400 supernovae in 394 different galaxies, with careful notes on the relationship between light curve (LC) decline, and the shapes (morphological characteristics ) of their host galaxies, They find some trends, and note that their sample is small, needing a longer look. They find 5 types of type 1a's...some more likely in older redder galaxies, and some in younger bluer galaxies.