Over the past decade or so, type Ia supernovae have served as useful cosmic beacons. Using them, astronomers have measured the value of the Hubble constant (which determines the rate of expansion of the Universe) to an accuracy of 10%, and discovered the existence of 'dark energy' (which is thought to drive the acceleration of the rate of expansion). Even so, astronomers are uncertain about the origins of these objects―what progenitor system leads to the creation of a type Ia supernova? Supernovae are categorized according to the different chemical elements identified in the spectra of the radiation they emit. Typically, type Ia supernovae are bright, and their spectra show no evidence of hydrogen. On page 651 of this issue, Hamuy et al. reveal that they have detected hydrogen in the spectrum of the supernova SN2002ic, which was discovered in November last year. Although in other respects SN2002ic fits the type Ia classification, the presence of hydrogen in its vicinity sets it apart from this class, but perhaps offers a clue to its progenitor system.
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