The Ring Nebula Is a Barrel, Not a Ring, 3D Data Show

Astronomers have constructed the clearest 3D view yet of the famous Ring Nebula, the gaseous remains the dying embers of a Sun-like star. Despite the circular shape, the nebula isn’t a sphere. Instead, the new work reveals that it’s an ellipsoid, shaped like a rugby ball thanks to the interaction of a binary system at its center. We only see it as round because we are looking down one of the nebula’s poles.

The Ring Nebula (also known as Messier  57) is a cosmic tombstone in the constellation Lyra, marking the life of a star much like the Sun. When that star reached the end of life, it ballooned in size before shedding its outer layers into space, like a snake dispensing with its skin. In a few billion years, a similar fate awaits our Sun. Traditionally, astronomers have tried to map remnants like the Ring Nebula using instruments such as the Hubble and James Webb space telescopes. These instruments are sensitive to hot gas and dust within the nebulae.

Now, a team led by Joel Kastner (Rochester Institute of Technology) have pioneered a different approach. The team used the Submillimeter Array (SMA) in Hawai‘i to peer at the carbon monoxide (CO) molecules hidden with the nebula. The CO is cold and tends to envelop the hotter material that was previously observed.

“The SMA allows us to accurately measure the velocities of the molecular gas in the nebula, so we can see what's moving toward or away from us,” Kastner says. The CO map thus allowed Kastner and his team to build a more detailed 3D interpretation of the Ring Nebula's structure than what has been constructed previously.

From this structure came some key insights. Firstly, the team could estimate the nebula’s age, suggesting it is a mere 6,000 years old — an astronomical infant.

Secondly, the astronomers spotted blobs of gas emerging at around 50 kilometers per second (more than 100,000 mph) from each end of the ellipsoidal shell. This fast-moving material flows outward through holes that are almost aligned with the spin axis of the original star — but not quite. The outflow is tilted with respect to the spin axis by about 10°. That misalignment suggests the gravitational influence of one or more companion stars.

The finding dovetails nicely with previous work on Webb observations, in which astronomers also put the nebula’s concentric rings down to the influence of a companion.

“I think this is a very nice study that settles some previous debates as to the actual 3D structure of the Ring Nebula,” says Roger Wesson (Cardiff University, UK), who was not involved in the research. “Determining the 3D structure of the nebula constrains its evolutionary history in a way that images alone cannot.”

In particular, Wesson says, the evidence for a binary companion “shows again that binarity plays a crucial role in the formation and evolution of many or even most planetary nebulae.”

Understanding planetary nebulae tells us not only about the Sun’s ultimate fate but also about how we came to be here. “The stars that generate planetary nebulae like the Ring . . . may have produced much of the carbon in the universe,” Kastner says. We are carbon-based lifeforms, after all. “We can watch that carbon on its way to being recycled into the next generation of stars and planets when we observe these amazing objects.”