After seeing the stunning images of the Southern Ring Nebula taken by the James Webb Space Telescope, scientists realised they would have to reevaluate their previous assumptions about this seemingly ordinary object.
The Southern Ring Nebula's oddly elongated and curved features were likely sculpted by at least two and probably three additional undiscovered stars, according to preliminary data from NASA's James Webb Space Telescope. In addition, for the first time, scientists were able to accurately localise the mass of the central star before it generated the nebula by combining Webb's infrared photos with existing data from the ESA's (European Space Agency) Gaia satellite.
The core star, according to scientific estimates, was approximately three times the mass of the Sun before it expelled its layers of gas and dust. Following these ejections, its mass has decreased to around 60% of the Sun's. To put together the image and speculate on how the forms in this nebula may have been produced, the researchers needed to know the starting mass, which they were able to do thanks to the discovery.
The Southern Ring Nebula is an example of a so-called planetary nebula, which despite its name is the result of the implosion of a red giant star and has nothing to do with planets. A red giant forms when a star with a mass similar to the sun runs out of hydrogen fuel in its core and expands to a size hundreds of times that of the original star. The nebula is the result of the red giant's shedding of its outer layers, and the white dwarf is the result of the red giant's contraction as it cools.
Hubble photos show the shed layers forming a very smooth ring-shaped cloud, with the white dwarf visible as a tiny point of light in the middle, dwarfed by a much brighter, yet fully alive companion star located around 1,300 solar radii distant.
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With his telescope, Webb revealed a more nuanced picture of the nebula. The Near Infrared Camera (NIRCam), which detects hotter objects like stars, and the Mid-Infrared Instrument (MIRI), which excels in detecting dust, were used to capture images of the cloud by the telescope of the century.
The image captured by MIRI instantly piqued the curiosity of astronomers. Hubble's vision, which previously revealed a single massive star and a much smaller companion, has now shown two stars of comparable size. The white dwarf that scientists had previously identified as a star instead appeared red.
Astronomers were immediately perplexed by the origin of the dust disc. These discs are often composed of debris from a companion star that orbits a more massive star and is perturbed by the larger star's gravity. But the white dwarf's known brilliant companion in the Southern Ring Nebula was too far away to be impacted by the white dwarf. According to De Marco, the dust could only be explained if a second, smaller star was circling the white dwarf considerably closer to the solar system. What had been a binary star system unexpectedly expanded to include a third star.
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The comparatively smooth surface of the ring-shaped cloud viewed by Hubble transformed into a mess of whirling streams and dust filaments under Webb's piercing scrutiny. The astronomers were particularly intrigued by the concentric layers that seemed to be radiating outward toward the ring's boundaries. Webb's pictures of the nebula around the big star WR140 show similar concentric shells, thus this is not the first time astronomers have spotted them.
De Marco elaborated that the distance between the concentric rings might tell scientists a lot about the companion star responsible for the formations, such as how far away it is from the white dwarf whose expelled envelope formed the nebula. The distance analysis revealed that the visible partner and the one responsible for the dusty disc were incompatible as the source of the ripples. The system now includes a third star located midway between the first two.
