has already produced a supernova impostor; and the brightest component, a Wolf–Rayet star, in the Regor or Gamma Velorum system. Others have gained notoriety as possible, although not very likely, progenitors for a gamma-ray burst; for example WR 104. Identification of candidates for a type Ia supernova is much more speculative. Any binary with an accreting white dwarf might produce a supernova although the exact mechanism and timescale is still debated. These systems are faint and difficult to identify, but the novae and recurrent novae are such systems that conveniently advertise themselves. One example is U Scorpii. The nearest known Type Ia supernova candidate is IK Pegasi (HR 8210), located at a distance of 150 light-years, but observations suggest it will be several million years before the white dwarf can accrete the critical mass required to become a type Ia supernova. See also List of supernovae List of supernova remnants References Further reading External links A searchable catalogue An open-access catalog of supernova light curves and spectra. Articles containing video clips Astronomical events Light sources Standard candles Stellar evolution Stellar phenomena Concepts in astronomy