The Hubble Constant from Blue Type Ia Supernovae

TL;DR

This study uses blue Type Ia supernovae, which are less affected by dust extinction, to measure the Hubble constant, finding values closer to CMB estimates and highlighting potential systematic effects in traditional methods.

Contribution

It introduces a method to determine the Hubble constant using blue supernovae, reducing dust correction uncertainties and aligning measurements with CMB results.

Findings

Blue supernovae yield a lower Hubble constant (~70 km/s/Mpc) closer to CMB values.

Using only blue supernovae reduces the Hubble tension by about 3 km/s/Mpc.

The current sample of blue supernovae is small, but future surveys will improve precision.

Abstract

There is a persistent tension of about $5\sigma-6\sigma$ between the value of the Hubble constant, as derived from the local distance ladder vs. the cosmic microwave background, signaling either unaccounted for systematics in the measurements or `new physics', such as early dark energy. Determining the Hubble constant using Type Ia supernovae requires nontrivial and accurate corrections for dust extinction. To circumvent this obstacle, we here determine the Hubble constant from blue, and hence presumably unextinguished, supernovae. For two different sets of Type Ia supernova data and lightcurve fitting methods, we find that when using blue supernovae only, the derived Hubble constant is consistently lower by $\sim$ 3 km s$^{-1}$ Mpc$^{-1}$ ($70 \pm 2.1$ and $70.3 \pm 3.0$ km s$^{-1}$ Mpc$^{-1}$), and within 1$\sigma$ of the cosmic microwave background measurement, compared to when using all supernovae. This is consistent with the hypothesis that systematic effects in dust corrections may affect standard supernova cosmology. However, the number of blue calibrating Type Ia supernovae is small (about six), and values of the Hubble constant for a range of different supernova colors are consistent at the 1.2$\sigma$ level. Upcoming major transient surveys will discover numerous unextinguished SNe~Ia, and thus be able to increase the precision of the Hubble constant measured from blue SNe~Ia, heralding a promising path toward resolving the Hubble constant tension.