WO stars represent a very brief stage in the evolution of massive stars, predicted to be the final evolutionary stage of massive stars with initial masses between 40 to 60 times the Sun’s mass. These remarkable stars are likely to explode as type Ic supernovae in ~1,000 to 10,000 years. Type Ic supernovae are a class of stellar explosions caused by the core collapse of massive stars that have shed their outer envelopes of hydrogen and helium. As a result, type Ic supernovae do not contain hydrogen and helium. For comparison, type Ib supernovae are another class of stellar explosions involving massive stars that have only shed their outer envelope of hydrogen.
Locations of several WO stars on the Hertzsprung-Russell diagram. Also indicated are several WC stars (i.e. carbon sequence Wolf-Rayet stars). Tramper et al. (2015).
Model showing the evolution of the surface mass fractions of the WO star WR102 since the onset of core-helium burning. Tramper et al. (2015).
Tramper et al. (2015), “Massive stars on the verge of exploding: the properties of oxygen sequence Wolf-Rayet stars”, arXiv:1507.00839 [astro-ph.SR]