Scientists say they were amazed by the structure of the Southern Ring Nebula

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The glorious, billowing Southern Ring Nebula is the cocoon of a dying star — and it has a secret.
Scientists have found this nebula to exhibit a double-ring structure that evidences not one, but possibly three stars at its heart.
The Southern Ring Nebula, also designated NGC 3132, is a planetary nebula located about 2,000 light-years away in the constellation of Vela, the Sails.
The name “planetary nebula” is a misnomer — such nebulas have nothing to do with planets.
The Southern Ring Nebula was imaged in December 2022 by the James Webb Space Telescope (JWST), which revealed molecular hydrogen gas forming the nebula’s “exoskeleton.”
The discovery of the second ring in the Southern Ring Nebula — or should that now be Southern Rings, plural?
— is prompting astronomers to revisit some of those other well-known ring nebulas to see if they have missed second rings in them, too.
“We’re seeing it generated in the sun-like stars that are dying, like the star that’s just died and created the Southern Ring.”

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The magnificent, voluminous Southern Ring Nebula is a dying star’s cocoon, and it conceals a mystery. Researchers have discovered that this nebula has a double-ring structure that suggests that it may have three stars at its core.

NGC 3132, also known as the Southern Ring Nebula, is a planetary nebula situated in the Vela constellation, which is the Sails, approximately 2,000 light-years away. Planetary nebulas are not related to planets, hence the term “planetary nebula” is misleading. Rather, they are the last breaths of dying sun-like stars, which change inside the chrysalis until they eventually bloom into white dwarfs. After the star’s red giant phase, its outer envelope is puffed off into space, forming a nebula.

The Southern Ring Nebula’s “exoskeleton” is made of molecular hydrogen gas, as shown by images taken of the nebula in December 2022 by the James Webb Space Telescope (JWST). Warm gas that is heated and illuminated by ultraviolet light emitted by the white dwarf itself is described as radiating at a temperature of roughly 1,000 kelvin, which is equivalent to 1,340 degrees Fahrenheit or 726 degrees Celsius. Only a small portion of the molecular gas in the nebula is represented by that exoskeleton, nevertheless.

Related: Beautiful new James Webb Space Telescope images show the Horsehead Nebula rearing its head (video).

The Submillimeter Array (SMA), a collection of eight radio telescopes atop Hawaii’s dormant volcano Mauna Kea, was used by a team led by Joel Kastner of the Rochester Institute of Technology to look for additional molecular gas in the nebula, specifically carbon monoxide gas. Within the nebula, carbon monoxide is mingled with hydrogen and other molecular gases, so measuring the amount of carbon monoxide is really a good way to measure the amount of all those other molecules that are harder to find. As expected, the SMA detected the distribution and velocities of the carbon monoxide molecules, indicating which ones are traveling in our direction and which are heading away.

“The Submillimeter Array shows us the colder carbon monoxide that you can’t see in the JWST image, while JWST showed us the molecules of hydrogen and how they stack up in the sky,” stated Kastner in a press release.

The Southern Ring is mainly shaped (from our perspective) like a ring, as its name implies. This ring is expected to expand as the nebula gradually grows before dispersing, as evidenced by the SMA observations. But the information also helped Kastner’s group map the molecular exoskeleton of the nebula in three dimensions. This brought with it a revelation. The scientists discovered a second ring that was perpendicular to the first, in addition to demonstrating that what we perceive to be a ring is actually just a lobe in a bi-polar nebula viewed end-on.

“We were shocked to discover there was another ring when we started to rotate the entire nebula in 3D and realized it was actually a ring,” Kastner said.

The peculiar configuration presents an intriguing trail of potentially three stars at the center of the nebula, instead of just one or two. The three stars, if they exist at all, are probably too close together or too faint to be resolved individually, even by the JWST. Only one of the stars, the most massive of the three, will have reached the end of its life.

There’s mounting evidence that some planetary nebulas—at least the ones with intricate structures—are created when a companion star interferes with the central dying star. Kastner’s group suggests that a third star, orbiting a close binary, is part of a triple system that includes the Southern Ring. The orbital radius of the third star is 60 astronomical units (AUs), which correspond to the distance between Earth and the sun. In our solar system, 60 AUs would be at the far edge of the Kuiper Belt.

The Southern Ring’s two lobes have an hourglass-shaped, narrow waistline, which is typical of planetary nebulas that originate from binary star systems where one of the stars is nearing the end of its life. Rather than allowing the material to escape in an equatorial direction, the binary companion manages to corral the material shed by the dying star, forming the two lobes. An abundance of infrared light from the central star system, a well-known indicator of a dusty disk created by interactions between a close binary companion and red giant, has been detected in the mid-infrared observations made by JWST, which lends credence to this theory.

That clarifies the meaning of the first ring. The group claims that it is less certain where the second ring originated.

Even though the Southern Ring looks to be bilobed, part of the material must have been released in the form of an approximately spherical or ellipsoidal envelope of material that the red giant threw off during a fast mass-loss event, which may have been its last material exhalation before leaving the white dwarf behind. If there is a third star, its gravity would affect the inner binary, causing the jets’ direction to “wobble,” like a spinning top. Nevertheless, the binary star system still produces a series of fast, narrow jets. The second ring would have been formed if those precessing jets had carved out a circular hollow in the ellipsoidal component of the nebula.

Although Kastner notes that this explanation is still conjectural, the structure of the nebula’s central ionized cavity does show evidence of such jets.

It has also been shown that other ring-shaped planetary nebulas, like the Helix Nebula (NGC 7293 in Aquarius), have bi-lobed structures, meaning that we are looking “down” the end of one lobe. Scientists are examining some of the other well-known ring nebulas to see if they have also overlooked second rings, after the discovery of the second ring in the Southern Ring Nebula. Or should that now be Southern Rings, plural?

Stellar death is not the only meaning associated with planetary nebulas. They also carry the hope of fresh life, almost literally.

Kastner asks, “Where does the carbon, oxygen, and nitrogen in the universe come from?”. “We are witnessing its generation in the dying sun-like stars, such as the star that recently passed away and formed the Southern Ring. “.

These molecules travel across space as an expanding planetary nebula expands into interstellar space, eventually congealing into massive molecular clouds that give rise to the next generation of stars and planets.

The planetary atmospheres would eventually contain a large amount of that molecular gas, and atmospheres are what support life, according to Kastner. Yes, every element on Earth that is heavier than hydrogen and helium was born inside a star and expelled into space when the star collapsed.

Indeed, as many experts like to say, we are made of star stuff.

Therefore, we can see the beauty of stellar death in nebulas like the Southern Ring as a star rising from the ashes to restart the cycle of star birth and death in the future. Everything that has happened before will happen again, to borrow a phrase from Battlestar Galactica.

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