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| Astronomers thought that the Southern Ring Nebula was quite unremarkable. Until they saw it through the eyes of the James Webb Space Telescope. (Image credit: NASA, ESA, CSA, and STScI) |
Astronomers realized they would have to reevaluate what they believed to be true about the unimpressive object when they first viewed the stunning images of the Southern Ring Nebula taken by the James Webb Space Telescope.
Located about 2,000 light-years distant from Earth in the constellation Vela, which is visible in the southern sky, the Southern Ring Nebula was among the James Webb Space Telescope's early research objectives, and a portrait was among the photos initially given to the world in July. The nebula, commonly known as NGC 3132, has been previously observed by Webb's predecessor, the Hubble Space Telescope. But Hubble's photos, although magnificent, failed to capture the entire reality of this dust cloud, which sprung up from an implosion of a dead star around the size of the sun barely 2,500 years ago.
"The Southern Ring Nebula was never regarded especially exceptional," Orsola De Marco, an astronomer at Macquarie University in Australia and a primary author of a new research investigating Webb's photos, told Space.com. "The nebula was renowned for having an extensive envelope and for containing two visible stars circling each other."
The Southern Ring Nebula is a so-called planetary nebula, which despite its name has nothing to do with planets and instead is the outcome of the implosion of a red giant star. A red giant, which may be hundreds of times wider than the original star, forms when a star around the size of the sun runs out of hydrogen fuel in its core. Eventually the red giant loses its outer layers (which subsequently create the nebula) and compresses into cooling leftovers termed a white dwarf.
In the photos from Hubble, the shed layers create a very smooth ring-shaped cloud, while the white dwarf can be seen as a minuscule speck of light at the center of the ring, outshone by a much brighter, yet fully alive, partner star some 1,300 sun-Earth distances distant.
Webb offered a more sophisticated image of the nebula. The Near Infrared Camera (NIRCam), which detects warmer objects like stars, and the Mid-Infrared Instrument (MIRI), which excels at detecting dust, are two of the instruments used by the telescope of the century to image the cloud.
It was MIRI's opinion that instantly piqued the astronomers' curiosity. Two stars of equal sizes appeared instead of the one big star and one tiny star seen in Hubble's view. And surprisingly, the star that the scientists recognized as the white dwarf was unexpectedly red.
White dwarfs are hot and don't glow in this wavelength, according to De Marco. "So, instantly, we understood that there must be a lot of cool dust enshrouding the white dwarf, there is a cool disk of dust."
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| An image of the Southern Ring Nebula by the James Webb Space Telescope's MIRI instrument reveals that one of the central stars is oddly red. (Image credit: NASA/ESA/CSA/STSCI) |
Astronomers started to question right away how the dust disk formed. Typically, the material that makes up these disks comes from a smaller star circling a larger star whose gravity perturbs the companion star. But the known brilliant companion of the white dwarf in the heart of the Southern Ring Nebula was too far away to be touched by the white dwarf. De Marco said that the only conceivable explanation was that a second, undetectable tiny star was circling the white dwarf very closely, spewing the dust. The system of two stars suddenly became a system of three.
But the shocks didn't stop there.
Under Webb's penetrating gaze, the relatively smooth surface of the ring-shaped cloud seen by Hubble, turned into a mass of swirling streams and dust filaments. Concentric layers that spread outward toward the ring's edges like pond ripples were one feature that the astronomers noticed in particular. Astronomers have observed such concentric shells previously, notably in Webb's photos of the nebula around a big star known as WR140.
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| A NIRCam image of the Southern Ring Nebula reveals concentric ripples in the ring-shaped cloud. (Image credit: NASA/ESA/CSA/STScI) |
"There are several nebulas with arches like that," De Marco remarked. "There's been a lot of work done on modeling of where [the arches] come from, and the only successful model is that you have an orbiting companion, and when the star ejects the nebula, the nebula streams past the orbiting companion that acts like a sprinkler and creates a spiral that is ingrained into the expanding nebula."
According to De Marco, astronomers can determine a lot about the companion star that produced the structures by calculating the distance between the concentric rings, including the companion star's separation from the white dwarf whose ejected envelope produced the nebula. The distance estimate revealed that neither of the two partners, the visible one and the one responsible for the dusty disk, could have generated the ripples. A third star, somewhere in between the two, was inserted into the system.
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| The view of the Southern Ring Nebula by the Hubble Space Telescope was far less exciting. (Image credit: NASA) |
The uninteresting nebula that nobody had been thrilled about suddenly became considerably more fascinating. Further examinations of the nebula's shape even suggested that a fifth star might be concealed within the dusty disk near the white dwarf, so the story wasn't quite over.
One of the study's co-authors, astronomer Joel Kastner of the Rochester Institute of Technology in New York, said: "We think all that gas and dust we see thrown all over the place [in the Southern Ring Nebula] must have come from that one star, but it was tossed in very specific directions by the companion stars" (opens in new tab).
The unanticipated finding of the obscure stars demonstrates how effective Webb is at revealing the mysteries of our cosmos.
The finding is presented in a paper(opens in new tab) published Thursday (Dec. 8) in the journal Nature Astronomy.
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