It’s ok, Darth Vader hasn’t got our humble planet in his sights!
No this Death Star is a binary system where both stars are locked into an orbit which will lead to their collision, unleashing a powerful gamma-ray burst when they do.
The object, WR104 is otherwise known as the ‘Pinwheel Star’ due to the presence of a spiral of dust engulfing the system.
Recent observations have accurately measured the orientation of the stars and thankfully they’re not pointed at the Earth. When they do eventually collide, it’ll be someone else’s problem.
WR104 is a Wolf-Rayet class star located 8,000 light-years from Earth in the constellation Sagittarius.
Wolf-Rayet stars are revealed by their spectra that show broad emission lines of ionised helium and highly ionised nitrogen or carbon.
They tend to have very high surface temperatures too and strong stellar winds. In the case of WR104, its surface temperature is around 44,000K that’s compared to the surface temperature of the Sun which is a mere 5,700K.
WR104 has a companion star though and they are both locked in their celestial dance that will ultimately end in their destruction.
The companion star is a more massive OB star and together they are creating a spiral dust pattern in that somewhat resembles a pin wheel – hence its name. The two are emitting powerful stellar winds that collide to form hydrocarbons or dust that form the spiral.
The system gained attention, not only due to its crazy appearance but because it’s also a potential supernova candidate and due to the concerns about potential gamma-ray bursts aimed at Earth. It’s this latter radiation risk that earned it the name ‘Death Star.’ Is it something we really need to worry about?
Initial studies suggested the pinwheel was rotating in the plane of the sky, indicating the stars’ rotational poles might be pointing toward us. If this was the case, then if one star ended its life as a supernova energetic enough to create a GRB, the resulting beam could be directed at our planet from within our own Galaxy.
In the latest study by Keck Observatory Instrument Scientist and astronomer Grant Hill, new spectroscopic observations using three Keck instruments—LRIS, ESI, and NIRSPEC (Low Resolution Imaging Spectrometer, Echellette Spectrograph and Imager and Near-Infrared Spectrograph)—have revealed a surprising twist.
While the pinwheel dust spiral appears face-on from Earth (spinning in the plane of the sky), Hill’s velocity measurements of the two stars revealed an unexpected finding: the actual orbital plane of the system is tilted at least 30-40 degrees from what was previously thought. Great relief! The system is not pointed directly at Earth as once feared, reducing the impact of any likely GRB.
It does however raise a question—how can the dust spiral appear face-on while the orbit is tilted? The mechanics of the system challenges existing models of dust formation in colliding wind systems and suggests additional, unknown physical processes may be influencing the formation of the dust plume!
Further studies are needed to try and unpick what’s going on at WR104 but as Hill says “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.”
He continues “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!”
Written by Mark Thompson/Universe Today.
