These latest Hubble observations of the Sombrero galaxy indicate only a tiny fraction of older, metal-poor stars in the halo, plus an unexpected abundance of metal-rich stars. Past major galaxy mergers are a possible explanation, though the stately Sombrero shows none of the messy evidence of a recent merger of massive galaxies. https://www.sciencedaily.com/releases/2020/02/200220135241.htm
