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All throughout the cosmos, planetary nebulae appear.
When lower-mass, Sun-like stars run out of fuel, they blow off their outer layers in a planetary nebula, but the center contracts down to form a white dwarf, which takes a very long time to fade to darkness. Some white dwarfs will shine for trillions of years; others are on their way to an inevitable supernova when they collide with another white dwarf or accumulate enough mass to detonate.
Displaying many different shapes, they all have the same cause.
After its formation some 4.6 billion years ago, the Sun has grown in radius by approximately 14%. It will continue to grow, doubling in size when it becomes a subgiant, but it will increase in size by more than 100-fold when it becomes a true red giant in another 7-to-8 billion years, total, all while growing in brightness by a factor of at least a few hundred. At the end of its life, it will expel its outer layers as its core contracts to a white dwarf, eventually triggering ionization of the surrounding material.
Inside, a Sun-like star is dying.
This animation shows how significant the fading of the Stingray Nebula has been since 1996. Note the background star, just to the upper left of the central, fading white dwarf, which remains constant over time, which confirms that the nebula itself is dimming significantly.
After blowing off its gaseous outer layers, its core contracts.
The Egg Nebula, as imaged here by Hubble, is a preplanetary nebula, as its outer layers have not yet been heated to sufficient temperatures by the central, contracting star to become fully ionized. Many of the giant stars visible today will evolve into a nebula like this before shedding their outer layers completely and dying in a white dwarf/planetary nebula combination. Despite its name, neither this nor the more-evolved planetary nebulae have anything to do with planets.
By contracting, it heats up, eventually ionizing its surroundings.
When the central star in a dying stellar system heats up to about temperatures of ~30,000 K, it becomes hot enough to ionize the previously ejected material, creating a true planetary nebula in the case of a Sun-like star. Here, NGC 7027 has just recently crossed that threshold, and is still rapidly expanding. At just ~0.1-to-0.2 light-years across, it is one of the smallest and youngest planetary nebulae known.
That characteristic ionization marks a full-fledged planetary nebula.
When our Sun runs out of fuel, it will become a red giant, followed by a planetary nebula with a white dwarf at the center. The Cat’s Eye Nebula is a visually spectacular example of this potential fate, with the intricate, layered, asymmetrical shape of this particular one suggesting a binary companion. At the center, a young white dwarf heats up as it contracts, reaching temperatures tens of thousands of Kelvin hotter than the surface of the red giant that spawned it. The hottest young white dwarf surfaces reach temperatures of 150,000 K or more.
The Red Spider Nebula, NGC 6537, is one among countless examples.
The Red Spider Nebula, NGC 6357, was taken with the ground-based New Technology Telescope at La Silla Observatory. The material was once thought to have a bipolar shape due to matter being funneled towards the progenitor star’s poles; that view is outdated, as the data now supports the presence of a binary companion for carving the nebula’s shape.
Discovered in 1882, its two lobes and bright features suggest a binary companion.
This 2001-era Hubble Space Telescope image of the Red Spider Nebula was the best view we had of this cosmic object for 24 years: until the first JWST NIRCam images of it were unveiled in late 2025. The waves visible in the gas hint at new, fast outflows overtaking and colliding with previous, slower-moving ejecta.
Individual, singlet stars usually make faint, ellipsoidally-shaped nebulae.
Around a variety of stellar corpses and dying stars, doubly-ionized oxygen atoms produce a characteristic green glow, as electrons cascade down the various energy levels when heated to extreme temperatures often exceeding ~50,000 K. Here, the planetary nebula IC 1295 shines brilliantly. These conditions are present in intense star-forming regions (including in the early Universe) and around stellar corpses, where the green phenomenon also helps color the so-called “green pea” galaxies, as well as Earth’s aurorae.
But a massive, orbital companion can create extended shapes,
The dying red giant star, R Sculptoris, exhibits a very unusual set of ejecta when viewed in millimeter and submillimeter wavelengths: revealing a spiral structure. This is thought to be due to the presence of a binary companion: something our own Sun lacks but that approximately half of the stars in the universe possess. Stars lose approximately half of their mass — some more, and some less — as they evolve through the red giant and AGB phases and into an eventual planetary nebula/white dwarf combination.
can carve bipolar ejecta,
This image shows six different, unrelated planetary nebulae, all with similar, bipolar
morphologies. These six objects, NGC 6302, NGC 6881, NGC 5189, M2-9, Hen 3-1475, and Hubble 5, are all destined to fade away after around 20,000 years.
and can lead to very bright ionization features.
These three bright planetary nebulae, all imaged by Spitzer, highlight features inherent to dying Sun-like stars with suspected binary companions. From left to right, the Exposed Cranium Nebula, the Ghost of Jupiter Nebula, and the Little Dumbbell Nebula all exhibit stellar winds, ejected material consisting of different elements, and a central, luminous stellar remnant. Only objects within a specific mass range will experience this phenomenon as their ultimate fate.
Credit: NASA/JPL-Caltech
The most famous, prominent planetary nebulae are all suspected to contain binary companions.
From their earliest beginnings to their final extent before fading away, Sun-like stars will grow from their present size to the size of a red giant (~the Earth’s orbit) to up to 5 light-years in diameter, typically. The largest known planetary nebulae can reach approximately double that size, but the overwhelming majority of bright planetary nebulae with intense ionization features are the result of binary systems, not singlet systems like our Sun.
Credit: Ivan Bojičić, Quentin Parker, and David Frew, Laboratory for Space Research, HKU
The Red Spider Nebula is no different, as JWST’s unparalleled imagery highlights.
This animation shows the same object, the Red Spider Nebula and the field around it, in two different sets of wavelengths of light: Hubble’s mostly optical views and JWST’s infrared views. At much longer wavelengths, JWST excels at capturing cooler features, molecular hydrogen, and ionized iron in a way that the Hubble data cannot.
The diffuse, glowing outer material is molecular hydrogen: shaped into two fully complete lobes.
This full-field view of JWST’s NIRCam image of the Red Spider Nebula (NGC 6537), the “tendrils” of the nebula can be seen to be just portions of two complete lobes of gas. At the estimated distance of the nebula, these lobes span approximately 6 light-years across, teaching us valuable information about the nebula’s age and the recent history of its ejecta.
A shroud of very hot, disk-like dust surrounds the central star.
This blown-up portion of JWST’s NIRCam view of the Red Spider Nebula shows the central region of the nebula, where the candidate white dwarf star suspected to be powering the nebula (inside the blue circle) is located. As the core of a dying Sun-like star contracts, it reaches temperatures of hundreds of thousands of degrees at its surface, leading to the ionization of the surrounding material.
Temperatures increase precipitously towards the nebula’s center.
The glowing red areas of the Red Spider Nebula, as seen with JWST’s NIRCam imagery, doesn’t indicate an intrinsic redness, but rather an increase in temperatures as we move from the nebula’s outskirts closer in towards the center. Neutral hydrogen at the outskirts gives way to a variety of ionized species, with temperatures rising to above 100,000 K at the central white dwarf!
Gas actively flows outward from the nebula’s core at a breakneck 300 km/s.
This JWST NIRCam image, with alternate coloration from the primary release image, shows off the dense material at the core, with different ionization signatures, temperatures, and brightnesses in that region. Ionized iron, in particular, appears in red/pink/white, drowning out the fainter green of neutral hydrogen gas at infrared wavelengths.
Ionized iron signatures trace an S-shape, as fast-moving stellar winds collide with the slower-moving lobes.
This portion of the JWST NIRCam composite of the Red Spider Nebula shows off a series of S-curved switchbacks in the material surrounding the nebula. These S-curves are thought to arise from fast-moving outflows overtaking and colliding with previously ejected, slower-moving neutral hydrogen gas.
The central white dwarf likely exceeds 150,000 K, potentially nearing 500,000 K.
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words.
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