Collectors of unusual astronomical objects have another to add to their list: the first spiral star ever observed. Elsewhere in this issue (Nature 398, 487–489; 1999) Peter Tuthill and colleagues report high-resolution infrared images of a spiral structure in the hot dust around a Wolf-Rayet star (WR104). They use a powerful aperture-masking technique at the 10-m Keck telescope in Hawaii to produce images much better even than those taken by the Hubble Space Telescope.

Wolf-Rayet stars are a phase in the life of exceptionally hot, massive stars, just before they are thought to become supernovae. Some Wolf-Rayet stars are surrounded by shells of dust, but it has been a mystery as to how dust survives the harsh ultraviolet radiation they emit.

Now, not only have Tuthill et al. detected a spiral pinwheel in the dust around WR104, but they also watched it rotate every 220 days. The image above shows the dusty spiral as seen in April and June 1998. The authors say the spiral and its rotation are the consequence of a companion star. In their hypothesis, dust is created around the binary star where the stellar winds collide, and is then carried along with the orbital motion.

Whether every dusty star has a binary remains open for debate. But in this case, the images of the spiral are so good that the orbital period, distance and separation of the binary system can be inferred from its effect on the stellar dust, without ever detecting the two central stars.