JWST puts a psychedelic spin on the Ring Nebula

August 14, 2023   Issue #603

Subscribers should put a ring on it

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Where I’ll be doing things you can watch and listen to or read about

I’ll be in New Jersey on October 17th giving an astronomy talk at a private school, which I’m excited about. My agent, Beth Quittman of Samara Speakers Agency, is hoping we can find some other venues in that area (NY, NJ, etc.) where I might be able to speak as well since I’ll be there anyway. If you’re someone who works for a museum, school, planetarium, science center, or anything related, and your organization would be interested in hosting me, please give Beth a ping! She’ll be happy to talk to you. I can talk about my book Under Alien Skies, the upcoming eclipses, and many other topics. Thanks!

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A cool or lovely or mind-bending astronomical image/video with a description so you can grok it

It’s not often you can say, “Here’s something like you’ve never seen it before!” but here I am, writing it: Here’s the Ring Nebula like you’ve never seen it before!

And it’s true:

This is the view of the Ring from JWST, which observes the sky in infrared light, invisible to our eyes. The detail is lovely, which doesn’t surprise me: The Ring is huge, about an arcminute across in the sky, almost big enough to be seen as a disk with the naked eye. While it’s too faint to see without a telescope, it’s easy even in small ‘scopes, and with a mirror 6.5 meters across JWST sees it as bright and in great detail.

The Ring, also called M 57, is what’s called a planetary nebula, located a little over 2,000 light-years from Earth. The name is a little misleading; when objects like it were first discovered they looked like planets, little discs, in the telescopes of the time. But they’re actually huge structures trillions of kilometers across — the Ring is well over two light-years wide — made of gas and dust cast off by stars like the Sun when they die. When a star runs out of nuclear fuel to fuse and generate energy, the outer layers puff up and can actually be ejected from the star as a wind of material. If the star is just sitting there, that wind will expand around it as a sphere, and what you see is a “smoke ring”, a bubble that looks empty in the middle and brighter around the edges.

For a long time that’s what everyone thought the Ring Nebula was. Then astronomers observed it with Hubble, and discovered it had lots of little dark dusty blobs scattered around it, but none in the space inside the ring. They reasoned that if it were spherical those blobs would be seen everywhere across it. They don’t, therefore the Ring isn’t a sphere.

It’s more like a barrel shape and we happen to be looking down the long axis! Most likely the central star either has another star as a binary companion (I found no evidence of this searching journals, though) or, when it expanded it engulfed planets orbiting it, and those spun it up. The end result is that more material was ejected along the star’s equator, forming a denser torus. Later, as hotter material from the interior of the star was exposed, the wind that blew out was faster and less dense, and was able to expand more freely up and away from the disk’s poles, creating huge elongated lobes, like a stretchy hourglass.

The dense knots are only in that torus, which is why we don’t see them toward the center. The outer halo is the oldest gas ejected from the star, moving outward into space and snowplowing up the gas already floating around there.

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The JWST image shows a lot of this. What you see in the image as violet colored is light emitted by molecular hydrogen (two hydrogen atoms bound together), which forms all that gribbly clumpy structure in the torus. The red stuff farther out is sooty material called dust, or more technically polycyclic aromatic hydrocarbons (or PAHs). As stars start to die the carbon in their atmospheres can link up to form these complex molecules (like Betelgeuse is doing right now). This happens early in the process, and that stuff can get farther away over time, which is why you see it on the outside (these outer shells or haloes can be seen in a phenomenal multi-telescope image created by Rob Gendler).

The green is interesting. That’s a wavelength of 2.8 – 3.2 microns, about 4 times longer than the reddest light you can see. I’m pretty sure that’s helium emitting that light; it emits at 3 microns, is common in planetary nebulae, and in Hubble images you can see it as a fuzzy dispersed glow across the nebula’s middle (in those images it’s colored blue). So that all fits.

You can also see lots of spikes on the outside, radial lines pointing away from the center. Those may be holes in the gas letting the light from the central star out, where it hits and energizes the gas outside the main ring. It’s like the rays of light you see from the Sun as they pass through gaps in clouds, lighting up haze in the air, except in this case the rays are trillions of kilometers long and the haze is actually gas leaked out by a dying star. Pretty cool. These spikes were seen in the older Hubble images, too.

The Ring is one of my favorite celestial objects to observe with my own telescope. It’s in the constellation Lyra, up high in the late summer, near the brilliant blue star Vega. Under low magnification it looks like a ghostly donut, a smoke ring hanging in the sky. It’s simply wonderful to see how the familiar friend looks when seen in such detail, and with light that we literally cannot see. There’s still so much to learn about how stars die, and this relatively nearby example of the process will yield the answers to many secrets.

Et alia

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