I would like to ask a question about the relation between the Hubble constant and the absolute magnitude of supernovae

I have read that supernovae alone cannot fix $H_0$ and that there is a degeneracy between $H_0$ and absolute magnitude. Why? How do Riess et al. find the absolute magnitude then?


1 Answer 1


Observation of Type Ia supernovae yield a redshift and an apparent magnitude at peak brightness. If you don't know the absolute magnitude at peak brightness then the apparent magnitude does not give you its distance. A measurement of distance, as well as redshift, is required to determine the Hubble parameter.

The absolute magnitude of Type Ia supernovae is determined from those that occur in (comparatively) local galaxies, where the distances are known by other means (e.g. Cepheid variables). See for example, Sandage et al. (1996); Altavilla et al. (2004).


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