‘Extreme stripping action’ led to disorderly birth of South Ring Nebula, Webb image reveals
Orsola DeMarco, Macquarie University
When the first five images from the James Webb Space Telescope (JWST) were unveiled, one of them stared at me with two eyes. It was an image of the South Ring Nebula, NGC3132, and right in the middle were two bright stars.
Now, the fact that NGC3132 is home to a binary star system (two stars orbiting each other) has been known since the days of the Hubble Space Telescope.
But in these early images, the central star that ejected the nebula – a tiny, hot white dwarf – was so faint it was almost invisible next to its bright Sun-like companion. Indeed, the nebula had one eye almost closed.
But the JWST reveals more than Hubble. It can collect “colder” photons (light particles) in the infrared range of the electromagnetic spectrum. In this cooler light, we saw the two stars of the binary system shine as bright as each other: two dazzling eyes!
This was surprising to any astronomer who understands this type of nebula; super hot white dwarfs generally do not glow in infrared light. It made sense for the cooler star to shine that way, but seeing the same glow from its partner was unexpected.
Emails began pouring in from coast to coast and across oceans as astronomers pieced together the puzzle. The central white dwarf star of NGC3132, they realized, is shrouded in dust. The dust is warmed by the heat of the star and therefore glows in the infrared, producing the light we observed.
This is what led us down the trail to find out what was really going on in the South Ring Nebula. Our findings from a team of nearly 70 astronomers are published today in Nature Astronomy.
At the core, a hot white dwarf
The South Ring Nebula is a planetary nebula. This means it is a gaseous nebula formed by a Sun-like star that loses most of its gas in the last act before it disappears.
Once it lost much of its mass, the star became a hot white dwarf. This central star now sits in the middle of the nebula, cooling like a stellar ember, effectively dying.
The beauty of planetary nebulae is that they can be examined forensically: parts of the nebula farther from the middle were ejected earlier in time. In this way, the whole nebula functions much like a geological record.
With its dying white dwarf in the center, our group approached NGC3132 like a crime scene.
Two unknown suspects emerge
First, we quickly realized that the dust that made the central star shine was actually a disk tightly wrapped around the central star that must have been forged by a companion. This orbiting companion star would have stripped gas from the central star, hastening its demise.
We haven’t spotted the companion, however. We believe it is either too faint to detect, or potentially perished in the interaction and merged with the central star.
Then we noticed something else: broken concentric arcs etched into the nebula’s extended halo. These also betrayed the presence of a companion in orbit. Could this culprit be the same one who forged the dust disk?
We do not think so. Although the arches have undergone some “alterations”, our measurements reveal the presence of another companion star. This one is placed a little too far from the central star to have created the dust disc.
And just like that, we had gathered evidence that the Southern Ring Nebula contains not just two stars in a binary system, but four.
And we would collect even more.
Tied up in a bumpy, gassy bubble
The “ring” that gives the nebula its name is actually the wall of an egg-shaped bubble containing hot gas, heated by the central star. This wall is marked with notable protuberances.
By combining the JWST image with data from the European Southern Observatory, our team created a 3D model that revealed that these prominences come in pairs, moving in opposite directions as they move away from the central star.
One possible explanation is that the interaction that created the dust disk did not involve just one close companion, but two. In other words, we’re looking at a potential fifth star in the mix – chaotically interacting with the central star to blast jets that repel these prominences.
The presence of this fifth star is still hesitant. But we can say with a good degree of certainty that the star system that created the Southern Ring Nebula includes not only the binary star system (the two eyes of the nebula), but also a third star that tore the gas to form the disc, and another which inscribed a pattern of concentric arcs in the gas bubble.
As for the nebula’s second eye – the one we had always known – it was definitely an innocent bystander. It is too far from the central star to have contributed to its disappearance.
One case closed, more to come
The case of the South Ring Nebula is not the only one to demonstrate how stars work in packs. Much of stellar astrophysics is being revisited today in light of the realization of how gregarious stars can be. And we are all the more delighted.
A myriad of phenomena arise from stellar interactions, from supernova explosions, to the merger of black holes and neutron stars giving rise to gravitational wave events.
As the JWST provides more detailed images of the universe, astronomers will be eagerly dusting off their gloves to tackle more mysteries.
Orsola De Marco, professor of astrophysics, Macquarie University
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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