  A type Ia supernova (SN Ia), one of the two main classes of exploding stars,
is recognized by the absence of hydrogen and the presence of elements such as
silicon and sulphur in its spectra. These explosions are thought to produce the
majority of iron-peak elements in the universe and are known to be precise
"standard candles" used to measure distances to galaxies. While there is
general agreement that SNe Ia are exploding white dwarfs, astronomers face the
embarassing problem that the progenitor systems have never been directly
observed. Significant effort has been put into the detection of circum-stellar
material (CSM) in order to discriminate between the different types of possible
progenitors systems, yet no CSM has been found. Here we report optical
observations of SN 2002ic which reveal large amounts of CSM seen as a strong
hydrogen emission. This observation suggests that the progenitor system
contained a massive asymptotic branch giant star which lost a few solar masses
of hydrogen-rich gas prior to the type Ia explosion.
