The headline here is a bit of an overstatement. Nothing in the original paper is casting doubt on Type Ia supernovae as reliable standard candles. It is definit

The headline here is a bit of an overstatement. Nothing in the original paper is casting doubt on Type Ia supernovae as reliable standard candles. It is definitely an embarrassment that we still don't know the mechanism by which Sne Ia occur, but empirically their luminosities can be calibrated well enough that the accelerating expansion of the universe is not in doubt. However, to determine the nature of dark energy (specifically, its equation of state), it may be necessary to calibrate SN Ia luminosities better, and that will probably require understanding exactly what they are. There are two major SN Ia models: the double degenerate, which involves two white dwarfs colliding, and the single degenerate, which involves one white dwarf accreting matter from a regular star. There have been two approaches to distinguishing between the two models. One is to look for hydrogen in the spectrum a long time after the supernova. In the single degenerate model the supernova shock will strip hydrogen from the companion star's atmosphere, but in the double degenerate model, there will be no hydrogen to strip. The other method is to look at the very early light curve of the supernova, as this paper did. The early light is expected to rise in a straight line as the surface area of the shock expands. A deviation from this straight line, particularly in the blue bands, then could indicate some interaction between the shock and a companion. This paper found such a "blue bump" in the early light curve of a recent supernova. (There has been at least one earlier paper that also found a blue bump in another supernova.) I'm out of the field now, so my knowledge isn't quite up to date, but my impression is that the observational evidence may be pointing to a mix between the two mechanisms. For anyone interested, I wrote a little bit about this problem here: https://joe-antognini.github.io/astronomy/typeia-progenitors https://joe-antognini.github.io/astronomy/typeia-progenitors