Anisotropic winds in a Wolf-Rayet binary identify a potential gamma-ray burst progenitor

The massive evolved Wolf-Rayet stars sometimes occur in colliding-wind binary systems in which dust plumes are formed as a result of the collision of stellar winds¹. These structures are known to encode the parameters of the binary orbit and winds^2-4. Here we report observations of a previously undiscovered Wolf-Rayet system, 2XMM J160050.7-514245, with a spectroscopically determined wind speed of 3,400 km s^-1. In the thermal infrared, the system is adorned with a prominent 12″ spiral dust plume, revealed by proper motion studies to be expanding at only 570 km s^-1. As the dust and gas appear to be coeval, these observations are inconsistent with existing models of the dynamics of such colliding-wind systems^5-7. We propose that this contradiction can be resolved if the system is capable of launching extremely anisotropic winds. Near-critical stellar rotation is known to drive such winds^8,9, suggesting that this Wolf-Rayet system may be a Galactic progenitor system for long-duration gamma-ray bursts.