Two-population modelling of type Ia supernovae and a revised Hubble constant measurement

by Dr Radoslaw Jan Wojtak (Niels Bohr Institute)

Friday 3 Oct 2025, 14:30 → 15:30 Asia/Kolkata

 

The Hubble constant tension is a 5sigma discrepancy between the CMB-based and SH0ES (distance ladder involving Cepheids and type Ia supernovae) measurements of the Hubble constant. It is not decisively ruled out or confirmed by alternative estimates of H_0 at low redshifts. It sparked a massive research wave based on the premise that the tension is a cosmological anomaly, but a wide range of extensions to the standard LCDM cosmological model proposed over the past 5 years fail to explain it. In my talk, I will focus on a new path of investigating systematic effects in the SH0ES measurement. I will show that several unresolved problems related to the currently used models of type Ia supernova standardisation (primarily unphysical dust extinction corrections) give rise to an intrinsic anomaly in the SH0ES calibration data and causes an overestimation of the Hubble constant. I will show that these problems and the anomaly itself can be resolved by employing an astrophysically better motivated two-population modelling of type Ia supernovae. The improved modelling accounts for differences between intrinsic and environmental (dust extinction) effects in supernovae originating from young (dust rich) or old (dust poor) stellar populations. Modelling these populations are relevant to quantify differences between young/star-forming calibration galaxies hosting Cepheids (selection effect) and supernova host galaxies in the Hubble flow which include both early and late types. I will show that the improved modelling of type Ia supernovae results in a reduction of the Hubble constant tension by at least 30 per cent and up to 50 per cent.