# How can one be sure that type-Ia supernovae have constant properties in time?

In this Wikipedia article there can be much read about type-Ia supernovae. One can read:

This type Ia category of supernovae produces consistent peak luminosity because of the uniform mass of white dwarfs that explode via the accretion mechanism. The stability of this value allows these explosions to be used as standard candles to measure the distance to their host galaxies because the visual magnitude of the supernovae depends primarily on the distance.

Could it be, however, that this (hypothesized) stability of the peak luminosity value is not constant in time? Let's assume the laws of physics didn't change since the big bang (this seems pretty obvious, but some physicists say these laws vary from place to place and from time to time).
This would imply that these "standard candles" can't be used for measuring the expansion rate of the Universe in the past? This, on its turn, could mean that dark energy may not exist after all (contrary to dark matter, the effects of which are certain, contrary to its Nature).

See also this question and this one.

• My guts feeling tell me something to do with Chandrasekhar mass limit – user6760 Jan 31 '20 at 12:59
• @user6760 That's indeed a constant in time. Given that the laws of physics don't change in time, which seems pretty obvious to me. But maybe the white dwarfs in earlier times were composed out of different material as they are later on. – Deschele Schilder Jan 31 '20 at 14:09
• you of course assume that physics does not change with time, otherwise you can make any predictions you want – Wolphram jonny Jan 31 '20 at 22:12
• and candles have a range of values, when you far two far away and supernovas are less trustworthy, you can use other methods, see here en.wikipedia.org/wiki/Cosmic_distance_ladder – Wolphram jonny Jan 31 '20 at 22:15
• @Wolphramjonny If you know how they change in time you can make them. – Deschele Schilder Feb 2 '20 at 23:00

## 1 Answer

There are some researchs about stars's metalicities that point that we can't use Supernovae Ia as standard candles as they dont explode always the same way. You can check some of this works in Arxiv.

Anyway this is true or not, the dark energy is not only backed up in Supernovae Ia. Microwave background radiation measurements, gravitational lensing, primitive nucleosynthesis of light elements and the large-scale structure of the universe confirm also the existence of dark energy.

• How do MBR measurements back up dark energy? – Deschele Schilder Feb 2 '20 at 22:57
• @descheleschilder Anysotropies in CMB give a value of the curvature of the universe and parameters of cosmological models: $\Omega_0$,$\Omega_{dm,0}$,$\Omega_{b,0}$,$\Omega_{\Lambda,0}$ (curvature, darkmatter, barionic and dark energy). – Isaac Domínguez Larrañaga Feb 3 '20 at 9:57
• Thanks. I'll ask a new question. – Deschele Schilder Feb 3 '20 at 11:07