Why standard dust models fail for supernova cosmology

Simulations of type Ia supernovae viewed through realistic galactic dust show that the standard exponential model for extinction—used in most supernova surveys—systematically undercounts faint, low-extinction events and overcounts heavily obscured ones. A two-parameter Weibull function fits the actual dust distribution far better and reveals that supernova intrinsic colors are ~2σ redder than previously thought, with implications for distance measurements used in dark energy studies.