UW News

December 8, 2022

NASA’s James Webb Space Telescope shows how several stars ‘stirred up’ the Southern Ring Nebula

Two dramatically different views of the Southern Ring Nebula captured by the JWST. Each image combines near- and mid-infrared light from three filters into a color image. The image on the left highlights the hot gas that surrounds the two central stars – one dim red star that originally shed the material that makes up the nebula, and a bright blue companion. The image on the right traces the star’s coldest and earliest molecular outflows that have reached farther into the cosmos.NASA/ESA/CSA/O. De Marco/J. DePasquale

Planetary nebulae are shells of gas and dust shed by certain types of dying stars, mostly likely including the sun in another 6 billion years. New data from NASA’s James Webb Space Telescope is shedding light on how and why these nebulae form.

At center of one planetary nebula, the Southern Ring Nebula, just a single star is visible in optical images, such as those taken by the Hubble Space Telescope. But the JWST has revealed that this star was merely a passive bystander when the nebula formed. A team of almost 70 astronomers, including Bruce Balick, a University of Washington professor of astronomy, used some of the first data from the new telescope to show that unseen companions shaped the intricate features of the nebula.

The source of the material in the Southern Ring Nebula is a tiny white dwarf star, as shown in some of the first JWST images released earlier this year by NASA, according to Balick.

In a study published Dec. 8 in Nature Astronomy, an international research team, led by Orsola De Marco of Macquarie University in Sydney, Australia, analyzed 10 highly detailed exposures taken by the JWST of the Southern Ring Nebula. Their calculations show the central star that ejected the expanding nebula gas was originally three times the mass of the sun. Today, after the ejections, it measures about 60% of the mass of the sun.

“The James Webb Space Telescope is already shaping up to be a powerful — indeed game changing — new tool in the quiver of telescopes used to study dying stars like that at the center of the Southern Ring. It is following the impact of the Hubble Space Telescope launched over 30 years ago,” said Balick. “Studying the nebulae such as the Southern Ring with the Webb provides key insights for exploring how stars evolve and disperse matter into their surrounding environments.”

The JWST images revealed details of the faint material around the outermost edges of the Southern Ring Nebula. This material, made up largely of cold dust and molecules, was the first to be ejected by the dying star about 1,000 years ago. Analyzing its current shape will help scientists understand how the ejection process began.

“With Webb, it’s like we were handed a microscope to examine the universe,” said De Marco. “There is so much detail in its images. We approached our analysis much like forensic scientists to rebuild the scene.”

“The pattern of the light from this aboriginal gas is far more complex than we had any right to anticipate,” said Balick. “For the first time we were able to see many devils in the details. Each of those devils has a story to tell. There’s no doubt that my field of research — the strange throes of dying stars — has already been forever changed by what we learn from these Webb images.  I am ecstatic at the scientific prospects of this new telescope. I should say ‘gobsmacked’!”

In order to explain the structure of the nebula revealed by the new images, the team has proposed that at least two close companion stars orbited the star at the center of the nebula as it shed its mass. During this intimate “dance,” the interacting stars may have launched two-sided jets, which appeared later as roughly paired projections that are now observed at the edges of the nebula.

“The gravity of these nearby orbiting stars extruded the newly ejected and outflowing gas into the complex nebula that we see today, much like taffy sold at carnivals,” said Balick.

Without those companion stars, the Southern Ring Nebula would likely be round and bubble-shaped like many other planetary nebulae.

“The [white dwarf] star is now smaller and hotter, but is surrounded by cool dust,” said co-author Joel Kastner at the Rochester Institute of Technology. “We think all that gas and dust we see thrown all over the place must have come from that one star, but it was tossed in very specific directions by the companion stars.”

Where are those companions now? They are either dim enough to hide, camouflaged by the bright lights of the two central stars, or have merged with the dying star.

In addition, a third, closely interacting star may have agitated the jets, skewing the evenly balanced ejections like spin art. And a fourth star with a slightly wider orbit might have “stirred the pot” of ejections, generating the enormous set of irregular rings in the outer reaches of the nebula.

“Sometimes I wish that the Earth were in orbit around the massive and optically visible star just off center in the Southern Ring Nebula since we would have front row seats to see the poorly understood mass ejection process,” said Balick. “Observing from the back bleachers 2,300 light years away may be safe, but it’s really frustrating.”

For more information, contact Balick at balick@uw.edu.  

Adapted from a press release by the Space Telescope Science Institute.