Pinwheel "Death Star" Discovery Shocks Astronomers

Astronomers have uncovered a new mystery surrounding a pinwheel-shaped star system—while, fortunately, revealing it is not likely to live up to its "death star" reputation. Located approximately 8,000 light-years from Earth in the constellation Sagittarius, the enigmatic star system WR 104 is renowned for its distinctive pinwheel-shaped nebula. New research led by W. M. Keck Observatory Instrument Scientist and astronomer Grant Hill has confirmed what scientists have long suspected—WR 104 comprises two massive stars: a Wolf-Rayet star and an OB-type main-sequence star, which orbit each other every eight months. The way that the spiral faces us head on had long led scientists to worry that—should the system go supernova—Earth could be hit with a deadly gamma ray burst. Lucky for us, but giving scientists a new mystery, the team found that the spiral of dust is angled differently to the orbits of the two stars. "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," explained 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!"

Wolf-Rayet stars are rare, massive stars with unusual spectra characterized by prominent broad emission lines of ionized helium and highly ionized nitrogen or carbon. These stars typically have masses greater than 25 times that of the Sun and are in an advanced stage of stellar evolution, having lost their outer hydrogen layers, leaving exposed helium cores. In WR 104, the interaction between the stellar winds of these stars generates a rotating spiral of dust, creating the system's striking pinwheel-like appearance. WR 104 first garnered media attention when scientists feared that its rotational axis was nearly lined up in the direction of Earth, raising concerns about the possibility of a gamma-ray burst (GRB) being directed toward our planet. This led to its dramatic nickname, the "Death Star." GRBs are intense bursts of gamma-ray radiation resulting from catastrophic events such as the collapse of massive stars into black holes or the merger of neutron stars. They are among the most powerful explosions observed in the universe. The immense energy released during a GRB can be harmful to life on Earth if one were to occur within our galaxy and be directed toward us. However, such events are extremely rare and typically occur at vast distances from our planet.

However, new findings have put those fears to rest. Scientists now understand that WR 104's orbital plane is tilted at least 30 to 40 degrees out of Earth's direct line of sight, significantly reducing the likelihood of a GRB impact. "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," says Hill. "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." Do you have a tip on a science story that Newsweek should be covering? Do you have a question about stars? Let us know via science@newsweek.com.

Reference

Hill, G. M. (2024). Is WR 104 a face-on, colliding-wind binary? Monthly Notices of the Royal Astronomical Society, 534(3), 2184–2195. https://doi.org/10.1093/mnras/stae2183