2,500 years ago, one of space’s most beautiful features was born: the Southern Ring Nebula. The nebula was vividly imaged by the Webb Space Telescope earlier this year, and astronomers now think they know exactly how a star’s violent outburst occurred, leaving the elegant nebula in its wake.
The star that bore the nebula was about three times the size of the Sun and 500 million years old. That’s quite young, in stellar terms; our Sun is about 4.6 billion years old and should live for another 5 billion.
Around 2,500 years ago, Confucius and the Buddha were still alive. The Peloponnesian Wars were about to kick off. And somewhere in those intervening years, a star 2,000 light-years away expired, blasting gas outward from a newly formed white dwarf.
The Southern Ring Nebula’s star is not dead—not yet—but its expulsion of gas is a major turning point in the star’s lifespan. White dwarfs are the stellar endgame; they form when stars have exhausted their nuclear energy and begin their slow cooldown.
Thanks to images from the Webb Space Telescope and clever calculations and mathematical modeling by the research team, the moments preceding the Southern Ring Nebula’s stellar light show can now be examined in detail.
Different Webb filters highlight various aspects of a light source, which is why some parts of the nebula may look pearlescent or a translucent red while others look blue or orange, depending on the image. The Webb image processors choose to highlight different aspects of objects in order to showcase various elements—hot gas, for example, or star factories within larger systems.
A team of 70 astronomers worked together to determine that as many as five stars (only two of which are now visible) may have been involved in the stellar demise. Their investigation of the star’s death is published today in Nature Astronomy.
“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,” said Orsola De Marco, an astronomer at Macquarie University and the study’s lead author, in a university release.
The team’s play-by-play of the nebula’s origins was possible thanks to very precise measurements of the most brilliant star (the star among stars, if you will) in the Webb image. Webb data enabled the researchers to precisely measure its mass and how far along in its own life it is, which in turn allowed them to derive the mass of the central faint star before it shed its material and created the colorful nebula.
Webb imaged the Southern Ring with two instruments, NIRcam and MIRI. The Webb images were supplemented by data from the European Southern Observatory’s Very Large Telescope, the San Pedro de Mártir Telescope, and NASA’s Gaia and Hubble space telescopes.
Only two of the stars thought to be involved in this cosmic rager are visible in Webb’s representative color snapshot of the nebula, taken with NIRcam. The bright star in the nebula’s center is partnered to the one that ejected so much material that it became a white dwarf. That wizened (and exhausted) star sits faintly along the 8 o’clock diffraction spike of the bright central star in the image above.
The astronomers believe that at least one star interacted with the fainter star (star 1 in the illustrated timeline below) as the latter swelled up, preparing to expel its gas and become a white dwarf.
According to the team, that mystery star (star 3) spewed out jets of material as it interacted with the dying star and cloaked the faint star in dust before merging with the dwarf. Star 2 in the illustration is the bright spot at the center of the nebula now—a comparatively stalwart character, given its lack of explosive activity or gassy releases.
Another star (or ‘partygoer’, in the Space Telescope Science Institute’s analogy of an astrophysical fête gone wrong) kicked up the gas and dust let loose by its predecessor, causing wavy ripples in the material. Then, another star (star 5 in the panels above) circled the light show and produced the ring system encircling the nebula.
By the researchers’ reckoning, you can consider the white dwarf near the nebula’s core to be the party host that raged way too hard and passed out well before the party’s end. But the star showed everyone a great time while it was up for it, and it’s thanks to it that the party lived on.
“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,” said Joel Kastner, an astrophysicist at the Rochester Institute of Technology, in an StScI release.
The researchers believe the same methods that uncovered specifics of the Southern Ring Nebula’s birth could help unpack the births of other nebulae, as well as the astrophysical forces at work in the interactions of stars.
The imagery that unveiled this interstellar scene was published in June; only now have researchers had the time to sift through the data and present their interpretation of it.