Sibling Rivalry: Thermonuclear Diversity and the Hubble Tension

TL;DR

This paper investigates how diversity in Type Ia supernovae affects measurements of the Hubble constant, demonstrating that accounting for thermonuclear diversity reduces the Hubble Tension significantly.

Contribution

It introduces a method to quantify and mitigate the impact of thermonuclear supernova diversity on cosmological parameter estimation, especially the Hubble constant.

Findings

Diversity in supernova light curves indicates multiple thermonuclear subclasses.

Accounting for diversity reduces the Hubble Tension from ~5σ to <1σ.

A strategy for precise H_0 measurement dominated by statistical uncertainties is proposed.

Abstract

Homogeneity is the hallmark of standard candle-based cosmology investigations. Thermonuclear supernovae (Type-Ia, SNeIa) violate this essential requirement if they develop along multiple evolutionary pathways. In this work, the impact of thermonuclear diversity on cosmological parameter constraints is quantified using Pantheon+, one of the largest ensembles of SNeIa compiled to probe cosmology to date. Evidence of diversity is encoded in supernova light curves. Pantheon+ is shown to be diverse, with features indicative of multiple thermonuclear sub-classes. Diversity-driven systematic effects have been quantified on a supernova-by-supernova basis; event selections based on light curve-derived metrics were subsequently used to characterize diversity-dependent trends and mitigate their impact. A "diversity free" estimate of the Hubble-Lema\^{i}tre parameter, $H_0$=$67.5\pm3.5$ km s$^{-1}$ Mpc$^{-1}$ (68\% C.L.), was obtained by reanalyzing Pantheon+. The Hubble Tension, an apparent disparity between early- and late-Universe determinations of $H_0$, is eased from $\sim$$5\sigma$ to $<$$1\sigma$ after accounting for the diverse thermonuclear scenarios that govern SNeIa. A strategy for precise determination of $H_0$, dominated by statistical rather than systematic uncertainties, is also presented.