New Dark Energy Survey Supernovae Results

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Some important cosmological results have just been announced by the Dark Energy Survey Collaboration. I haven’t had time to go through them in detail but I thought it was worth doing a quick post here to draw attention to them. The results concern a sample of Type Ia supernovae (SN Ia) discovered during the full five years of the Dark Energy Survey (DES) Supernova Program, which contains about 1500 new Type Ia Supernovae that can be used for cosmological analysis. The paper is available on the arXiv here; the abstract is:

The key numerical result of interest is the equation-of-state parameter for dark energy, designated by w, which occurs in the (assumed) relationship between pressure p and effective mass density ρ  of the form p=wρc2. A cosmological constant – which for many cosmologists is the default assumption for the form of dark energy – has w=-1 as I explained here. This parameter is one of the things Euclid is going to try to measure, using different methods. Interestingly, the DES results are offset a bit from the value of -1, but with quite a large uncertainty.

While the results for the equation-of-state parameter are somewhat equivocal, one thing that is clear is that the new SNIa measurements do confirm the existence of dark energy, in that the data can only be described by models with accelerating expansion, as dramatically demonstrated in this Figure:

I think this figure – or versions of it – will very rapidly appear in public talks on cosmology, including my own!

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