- Wolf-Rayet 104 is a star system where two massive stars orbit each other. A huge spiral of dust circles around the stars, making it a rare pinwheel star system.
- The pinwheel faces right toward us, so astronomers thought the poles of the stars did also. This could present a danger to Earth. Why? If one of the stars exploded in a supernova, it could send a powerful gamma-ray burst directly toward our solar system.
- But that isn’t likely to happen, new research from the Keck Observatory shows. The stars’ poles are tilted so much that any gamma-ray burst coming from them would miss us.
Meet Wolf-Rayet 104, the ‘pinwheel death star’
Wolf-Rayet 104 is a famous, rare type of star system known as a pinwheel star. Discovered in 1999, astronomers suspected it consists of two massive stars orbiting each other. As the stars orbit, their stellar winds collide, producing huge amounts of dust. The dust rotates in a giant pinwheel shape. Astronomers using the W. M. Keck Observatory in Hawaii said on March 18, 2025, that they have now confirmed the pair of stars. In addition, they also determined there is little to no danger of Wolf-Rayet 104 emitting a dangerous gamma-ray burst directly toward Earth, as astronomers had previously thought could happen. So the pinwheel death star will seemingly spare us from extinction. Phew!
Astronomer Grant Hill at the Keck Observatory is the author of the latest peer-reviewed research paper. He originally published it in the Monthly Notices of the Royal Astronomical Society on September 19, 2024. Keck issued the new press release on March 18, 2025.
2025 EarthSky lunar calendar is available now. A unique and beautiful poster-sized calendar with phases of the moon for every night of the year. Get yours today!
A rare pinwheel star
Astronomers discovered Wolf-Rayet 104 back in 1999. It is a rare pinwheel star system due to the huge spiral formation of dust circling a pair of stars. Scientists now suspect it’s actually a triple system, with a third much more distant star connected by gravity. But the pinwheel effect is created by the two main stars. The first of the two is a Wolf-Rayet star. Those stars are hot, bright and massive. Its stellar wind, similar to our sun’s solar wind, is rich in carbon. The other star, an OB star, is even more massive, and its solar wind is mostly hydrogen.
The stellar winds are huge streams of charged particles, or plasmas, flowing out from each star. As the two stars orbit each other, their stellar winds collide, forming hydrocarbon dust. That dust rotates in a giant pinwheel shape around the stars, and it glows brightly in infrared.
Is Wolf-Rayet 104 a pinwheel death star?
As it happens, Wolf-Rayet 104’s orientation is such that the pinwheel looks face-on to us. That adds to its beauty, but it also concerned astronomers. Why? It meant the rotational poles of the two stars might be aimed right toward us. Astronomers expect that one or both of the stars will likely explode in a supernova at some point in the future. That explosion could be powerful enough to produce a gamma-ray burst (GRB). And if that pole on the star was indeed oriented toward us, then the gamma-ray burst would come right toward our solar system, endangering life on Earth.
But based on the new study, however, it appears that’s not be the case. Hill explained:
Our view of the pinwheel dust spiral from Earth absolutely looks face-on (spinning in the plane of the sky), and it seemed like a pretty safe assumption that the two stars are orbiting the same way. When I started this project, I thought the main focus would be the colliding winds and a face-on orbit was a given. Instead, I found something very unexpected. The orbit is tilted at least 30 or 40 degrees out of the plane of the sky.
“WR 104 you ARE NOT the father…I mean “Death Star,” – Maury Povich. Keck Observatory proves what astronomers have suspected for years. Earth is spared from a potential gamma-ray burst from WR 104…but how?? ? keckobservatory.org/pinwheel/ ??W. M. Keck Observatory/Adam Makarenko
— W. M. Keck Observatory (@keckobservatory.bsky.social) 2025-03-21T17:31:36.177Z
Another surprising mystery
That 30 to 40 degrees is a healthy margin, meaning any gamma-ray burst would most likely miss us. But why is the dust spiral so tilted relative to the orbits of the stars? That is another mystery researchers will now have to solve. As Hill surmised:
This is such a great example of how, with astronomy, we often begin a study and the universe surprises us with mysteries we didn’t expect. We may answer some questions but create more. In the end, that is sometimes how we learn more about physics and the universe we live in. In this case, WR 104 is not done surprising us yet!
Bottom line: A new study from the Keck Observatory confirms two massive stars in the pinwheel death star won’t send a gamma-ray burst toward Earth after all.
Source: Is WR 104 a face-on, colliding-wind binary?
Via W. M. Keck Observatory
Read more: Spiral arms around a star, made by a giant planet
Read more: Keck Planet Finder begins search for other Earths