"Using host galaxy spectroscopy to explore systematics in the standardization of Type Ia supernovae" - Dixon et al. (2022)

Our Universe is expanding, and indeed accelerating in that expansion, and primary means to that discovery last century was measuring the apparent brightness of exploding stars known as supernovae. A special kind of supernova explodes at (almost!) the same brightness, known as Type 1a, and hence if you measure that brightness you can figure out how far away they are relative to each other - 100 times fainter? It must be 10 times further… What researchers found is that the mor distance supernovae are vastly fainer than expected meaning the universe wasn’t just growing it was in fact running away in that growth.

Fast forward to this decade and my student Mitchell Dixon published an exhaustive analysis of how to better calibrate that brightness of the Type 1a supernovae, in particular showing that they depended on the dust in the galaxy (slightly dimming them, or else perhaps causing a slightly different explosion brightness).