The messy death of a star

A global forensic team of astronomers led by Australia’s Macquarie University reconstructs using stunning James Webb Space Telescope images

Around 2500 years ago, a star ejected most of its gas, forming the beautiful Southern Ring Nebula, NGC 3132, chosen as one of the first five image packages from the James Webb Space Telescope (JWST).

A team of nearly 70 astronomers from 66 organisations across Europe, North, South and Central America, and Asia have used the JWST images to piece together the messy death of this star.

“It was nearly three times the size of our Sun, but much younger, about 500 million years old. It created shrouds of gas that have expanded out from the ejection site, and left a remnant dense white dwarf star, with about half the mass of the Sun, but approximately the size of the Earth,” says Professor Orsola De Marco, lead author on the paper, from Macquarie University’s Research Centre for Astronomy, Astrophysics and Astrophotonics.

The Webb Space Telescope offers dramatically different views of the same scene! Each image combines near- and mid-infrared light from three filters.At left, Webb’s image of the Southern Ring Nebula highlights the very hot gas that surrounds the central stars. This hot gas is banded by a sharp ring of cooler gas, which appears in both images. At right, Webb’s image traces the star’s scattered outflows that have reached farther into the cosmos. Most of the molecular gas that lies outside the band of cooler gas is also cold. It is also far clumpier, consisting of dense knots of molecular gas that form a halo around the central stars. Photo credits: SCIENCE: NASA, ESA, CSA, STScI, Orsola De Marco (Macquarie University) IMAGE PROCESSING: Joseph DePasquale (STScI)

“We were surprised to find evidence of two or three companion stars that probably hastened its death as well as one more ‘innocent bystander’ star that got caught up in the interaction,” she says.

The study was based on the JWST images supplemented by data from the ESO Very Large Telescope in Chile, the San Pedro de Mártir Telescope in Mexico, the Gaia Space Telescope, and the Hubble Space Telescope.

It paves the way for future JWST observations of nebulae, providing insight into fundamental astrophysical processes including colliding winds, and binary star interactions, with implications for supernovae and gravitational wave systems.

“When we first saw the images, we knew we had to do something, we must investigate! The community came together and from this one image of a randomly chosen nebula we were able to discern much more precise structures than ever before. The promise of the James Webb Space Telescope is incredible,” says De Marco, who is also president of the International Astronomical Union Commission on Planetary Nebulae.

Examine the straight, brightly-lit lines that pierce through the rings of gas and dust around the edges of the Southern Ring Nebula in the Webb Space Telescope’s image. These “spokes” appear to emanate from one or both of the central stars, marking where light streams through holes in the nebula. The holes are evidence of where the dimmer star that created this scene shot out material, creating open pathways for light to flow through. Photo credits: SCIENCE: NASA, ESA, CSA, STScI, Orsola De Marco (Macquarie University) IMAGE PROCESSING: Joseph DePasquale (STScI)

Astronomers gathered online and developed theories and models around the mid-infrared image to reconstruct just how the star had died.

Shining at the centre of the nebula is an ultra-hot central star, a white dwarf that has burned up its hydrogen. “This star is now small and hot, but is surrounded by cool dust,” said Joel Kastner, another team member, from the Rochester Institute of Technology USA. “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.”

There are also a series of spiral structures moving out from the centre. These concentric arches would be created when a companion orbits the central star while it is losing mass. Another companion is further out and is also visible in the picture.

How did all the “partygoers” – up to five stars – create the Southern Ring Nebula? Let’s hit “rewind” and replay the interactions that might have created the scene! First, it’s important to know that none of these illustrations are properly scaled, and three or as many as four of the stars would be too small and dim to appear in Webb’s image. Second, star 1 and star 2 are the only stars we see in the sixth and final panel above. The remaining “guests” will be known as stars 3, 4, and 5. They are all much less massive – in other words far smaller and dimmer – than stars 1 and 2. The first illustration shows a wider field. Star 1, the most massive of this group of five stars, is the fastest to age and is responsible for creating the planetary nebula. Star 2 very slowly orbits star 1, which is easier to see in the last panel. All is relatively quiet at this stage as they orbit one another, though there is another star on the scene, number 5. It orbits star 1 far more tightly than star 2 does. Cue the action! The second panel zooms way in on the scene – and two other companions appear in view. Star 1 has begun to swell as it ages rapidly, swallowing star 3. Through gravity, star 3 starts to draw in material from star 1 and launches jets in both directions. Star 4 is close by, but not yet interacting. The third panel shows how much star 1 has expanded as it ages. Two companions also enter the mix. Stars 3 and 4 have sent off a series of bipolar jets. As these two stars interact, the jets they sent out are tumbled, which leads to the irregular, wavy edges of the gas and dust ejected by aging star 1. Both companions 3 and 4 are interacting within the gas and dust star 1 has ejected. In panel 4, we zoom out to see more of the scene. Ultraviolet light and a fast, spherical wind from the newly exposed ultra-hot core of star 1 is helping to carve out its previously ejected gas and dust, creating a bubble-like cavity. There is also a leftover disk of

Looking at a three-dimensional reconstruction of the data, the team also saw pairs of protuberances that may occur when astronomical objects eject matter in jet form. These are irregular and shoot out in different directions, possibly implying a triple star interaction at the centre.

De Marco says: “We first inferred the presence of a close companion because of the dusty disk around the central star, the further partner that created the arches and the super far companion that you can see in the image. Once we saw the jets, we knew there had to be another star or even two involved at the centre, so we believe there are one or two very close companions, an additional one at middle distance and one very far away. If this is the case, there are four or even five objects involved in this messy death.” (Newswise)