About the image. Drawn after the pinwheel of WR 104: a hot, blue-white star with a spiral of dust curling out from it as it orbits a companion. The real spiral is seen almost face-on and is far too small and distant to show the stars; the details are imagined.
In 1867 two French astronomers at the Paris Observatory, Charles Wolf and Georges Rayet, noticed three stars in Cygnus with strange spectra. Instead of the dark absorption lines of ordinary stars, they showed broad, bright emission bands. Stars of this kind are now called Wolf–Rayet stars, and they are among the most extreme stars known.
Stars without their outer layers
A Wolf–Rayet star is a massive star that has lost its hydrogen envelope. Some blew it away in powerful winds, others had it pulled off by a companion star. What remains is the hot, exposed interior, rich in helium and in the nitrogen or carbon made by nuclear burning. Their surfaces range from about 20 000 K (19 730 °C) to about 210 000 K (209 730 °C); the hottest known, WR 102, is many times hotter than the Sun’s 5 772 K (5 500 °C).
Their winds are ferocious, thousands of kilometres per second, and those broad emission lines come from the hot gas streaming away. About 600 to 700 Wolf–Rayet stars are known in the Milky Way.
Pinwheels and shells
When a carbon-rich Wolf–Rayet star orbits another massive star, their winds collide and dust can form in the shock. In 1999 Peter Tuthill and colleagues used the Keck telescope to photograph WR 104, about 8 400 light-years away, and found a perfect spiral of dust, like a rotating garden sprinkler. The pinwheel turns once every 241.5 days, following the orbit of the two stars.
WR 140 makes dust in bursts instead. Its two stars swing close together every 7.9 years, and each time they make a new shell of dust. In 2022 the James Webb Space Telescope imaged 17 of these nested shells; later images showed them expanding at more than 2 600 kilometres per second. In 2023 Webb also photographed WR 124, wrapped in a clumpy halo of gas and dust it had thrown off.
Endings
Wolf–Rayet stars are close to the end of their lives. They are expected to explode as Type Ib or Ic supernovae, the kind of explosion without hydrogen. In rare cases the collapse of such a star may produce a gamma-ray burst. There has been speculation that WR 104 might one day aim one at Earth, but measurements of its tilt disagree and the chance appears to be small.
How long to get there?
Wolf–Rayet stars is about 8 400 light-years away (WR 104, the pinwheel).
Light299 792 km/s8 400 years
Breakthrough Starshotplanned light sail, 20% of light speed42 000 years
Parker Solar Probefastest spacecraft so far, 192 km/s13.1 million years
Voyager 1leaving the Solar System, 17 km/s148.1 million years
At Voyager 1's speed the trip would take about 1 851 656 human lifetimes of 80 years. Bars are on a logarithmic scale. Speeds: NASA, Breakthrough Initiatives.
Gallery
A blue-white star at the centre of swirling orange dust that curls around it, an impression of a Wolf–Rayet star and its dust spiral. AI-generated painting.A bright star with sharp light spikes at the centre of many faint, nested orange rings of dust, an impression of the Wolf–Rayet star WR 140. AI-generated painting.Wolf–Rayet stars, 3D artist's impression, rendered from the interactive model.Wolf–Rayet stars, 3D artist's impression, from another angle, rendered from the interactive model.Wolf–Rayet stars, 3D artist's impression, close-up, rendered from the interactive model.
Timeline
1867Charles Wolf and Georges Rayet find three unusual stars in Cygnus.
1999The dust pinwheel of WR 104 is imaged with Keck.
2022JWST images 17 dust shells around WR 140.
2023JWST photographs WR 124 and its nebula.
Questions people ask
What is a Wolf–Rayet star?
A massive star that has lost its outer hydrogen layers, exposing an extremely hot core with powerful winds.
What is the hottest star?
Among the hottest known is the Wolf–Rayet star WR 102, at about 210 000 K (209 730 °C).
Is WR 104 dangerous?
Probably not. There has been speculation that it could produce a gamma-ray burst aimed at Earth, but its tilt is uncertain and the chance appears small.