Famed WR 104 ‘pinwheel’ star reveals another surprise… and some relief

Decades of W.M. Keck Observatory research on the famed Wolf-Rayet 104 “pinwheel star” system has taken a new turn, revealing more mystery but reducing concerns about its potential as the “Death Star.”

A study led by W. M. Keck Observatory instrument scientist Grant Hill confirms that Wolf-Rayet 104 (WR 104) consists of two massive stars orbiting each other every eight months, generating a distinctive pinwheel of dust that glows in infrared. However, Hill’s findings challenge previous assumptions about its orientation, revealing that the system’s orbit is tilted at least 30 to 40 degrees—diminishing the likelihood of a gamma-ray burst aimed at Earth.

“Our view of the pinwheel dust spiral from Earth absolutely looks face-on, and it seemed like a safe assumption that the two stars were orbiting the same way,” Hill said. “Instead, I found something very unexpected.”

WR 104, first discovered at Keck Observatory in 1999, captured astronomers’ attention for its striking pinwheel structure formed by colliding stellar winds. Initial models suggested the system’s rotational poles might be pointed toward Earth, raising concerns that a future supernova could generate a gamma-ray burst in our direction. The new findings, published in the “Monthly Notices of the Royal Astronomical Society,” suggest otherwise.

Hill used spectroscopy data from three Keck Observatory instruments on Maunakea—LRIS, ESI, and NIRSPEC—to measure stellar velocities and analyze the system’s orbit. The unexpected tilt raises new questions about the relationship between the dust spiral and the binary stars’ motion.

“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” muses Hill.  “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.”