Temperature inhomogeneities cause the abundance discrepancy in H II regions

The established paradigm in astrophysics for determining the chemical composition of ionized nebulae (H II regions) has long relied on spectral line analysis. However, this paradigm has been in a state of crisis for over 80 years due to the "abundance discrepancy": a persistent, systematic difference between abundances calculated from strong collisionally excited lines (CELs) versus weaker recombination lines (RLs). This paper proposes a revolutionary resolution by establishing that temperature inhomogeneities within the nebulae, a previously unconfirmed hypothesis, are the definitive cause of this discrepancy, thus initiating a shift toward a new paradigm where these inhomogeneities are a fundamental parameter.

This paper is classified as a Model Revolution because it provides a decisive solution to a long-standing anomaly that had plunged its field into a model crisis. For decades, multiple competing hypotheses attempted to explain the abundance discrepancy. The authors present the first general observational evidence that strongly supports the temperature inhomogeneity hypothesis, demonstrating a clear physical cause for the discrepancy. By doing so, they invalidate other competing theories and propose a revised framework that fundamentally changes how chemical abundances are calculated, calling for a revision of past results and altering future observational strategies.