Travel the universe with Dr. Ethan Siegel as he answers the biggest questions of all
The Twin Jet nebula, shown here, is a stunning example of a bipolar preplanetary nebula. At the center, a dying star is in the final stages of life where it produces its energy via nuclear fusion, while the outer layers are highly evolved but illuminated only by reflected light. We’re still working to understand exactly how our Sun will appear when it becomes a planetary nebula in the distant future. (ESA, HUBBLE & NASA, ACKNOWLEDGEMENT: JUDY SCHMIDT)
Before a white dwarf and a planetary nebula, this is a living star’s final stage.
Our Sun is destined to someday die in a known, predictable way.
The evolution of a solar-mass star on the Hertzsprung-Russell (color-magnitude) diagram from its pre-main-sequence phase to the end of fusion. Every star of every mass will follow a different curve, but the Sun is only a star once it begins hydrogen burning, and ceases to be a star once helium burning is completed. (WIKIMEDIA COMMONS USER SZCZUREQ)
Like all Sun-like stars, it will leave a white dwarf/planetary nebula combination behind.
The red spiders nebula, shown here, has ripples and shock waves throughout its gas, due to the ultra-high temperature of its parent star: one of the hottest stars to form a planetary nebula in the known Universe. Planetary nebulae are self-luminous, as the central white dwarf heats the gas to temperatures over ~30,000K, causing the gas to give off its own emitted light. (ESA & GARRELT MELLEMA, LEIDEN UNIVERSITY, THE NETHERLANDS)
However, there’s a unique phase preceding that final transition: a preplanetary nebula.
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. Although similar in many ways to the Boomerang Nebula, it is at a much higher temperature. (NASA)
In the final stages of a red giant star’s life, its core runs out of fusible helium.
The Sun, today, is very small compared to giants, but will grow to the size of Arcturus in its red giant phase, some 250 times its current size. Red giants fuse helium into carbon, which becomes the first element created purely in stars rather than in the Big Bang. Carbon is the 4th most abundant element in the Universe today, and red giants are the primary means of producing it. (ENGLISH WIKIPEDIA AUTHOR SAKURAMBO)
The star pulses internally, fusing hydrogen in a shell surrounding the core.
The Frosty Leo Nebula, shown here, all arises from a single star approaching the end of its life. Its central star still shines, fusing hydrogen into helium in a shell around its core, but the core has run out of helium fuel to fuse into carbon and oxygen. The cloudiness arises from ejected gas from the star’s outer layers, and is composed mostly of hydrogen. (ESA/HUBBLE & NASA)
These fusion bursts eject the diffuse star’s outer, hydrogen gas layers.
The Red Rectangle Nebula, so called because of its red color and unique rectangular shape, is a protoplanetary nebula in the Monoceros constellation. It is part of a binary star system, where one member is ejecting the hydrogen gas in the post-AGB phase. This system will someday evolve, but has not yet evolved, into a full fledged planetary nebula. (ESA/HUBBLE & NASA)
The central star’s light reflects off the surrounding cool, dark gas.
The Water Lily Nebula in the constellation of Ara is one of the proto-planetary nebulae where complex organic molecules with aliphatic and aromatic structures are found. The surrounding gas is illuminated by the central star, but is not (yet) self-luminous. (SUN KWOK, BRUCE HRIVNAK, AND KATE SU; ESA/HUBBLE & NASA)
In the early stages of a preplanetary nebula, hydrogen gas is expelled in a roughly spherical fashion, before transitioning to a bipolar shape. The spiral pattern is thought to emerge if the star ejecting the matter is part of a binary system, which is not uncommon. Approximately 50% of the stars in the Universe are parts of multi-star systems. (ESA/NASA & R. SAHAI)
The remaining surrounding gas evolves from a spherical to an axial shape.
The Cotton Candy Nebula, shown here, shows evidence of both the spherical ejecta, visible in the ring-like structures, as well as the bipolar ejecta, which occur later and smash into the pre-existing gas, creating these knotted structures. The central star is in a phase where it burns hydrogen in a shell around an inert core exhausted of helium, blowing off the last bit of hydrogen still surrounding it. (ESA/HUBBLE AND NASA; ACKNOWLEDGEMENT: JUDY SCHMIDT)
This protoplanetary nebula shows clear evidence of the bipolar configuration, with two axially symmetric jets of matter. The central star, still alive, can be seen between the two lobes. The surrounding gas is not self-luminous, but only reflects the light from the central star. (ESA/HUBBLE & NASA)
This nebula, known as the Westbrook Nebula, is another example of a preplanetary nebula that has clearly evolved to the stage where the ejected gas has undergone collisions and turbulent processes, creating a series of characteristic knots. The gas here is not self luminous, but only reflects the light from the dying star that emitted it. (ESA/HUBBLE & NASA)
All the while, the central core contracts and heats up.
A color-coded image of the Boomerang Nebula, as taken by the Hubble Space Telescope. The gas expelled from this star has expanded incredibly rapidly, causing it to cool adiabatically. It is a pre-planetary nebula, illuminated by the central star that is in the post-AGB phase, but has not yet become a true planetary nebula. (NASA/HUBBLE/STSCI)
When the gas is exhausted and the core reaches ~30,000 K, the nebulous material finally ionizes.
The rotten egg nebula, at lower right (and shown in detail in the inset box, as imaged by Hubble) is a preplanetary nebula that’s part of a larger star cluster that also contains a full-blown planetary nebula, at the upper left. Whereas planetary nebulae are emission nebula, preplanetary nebulae only reflect the light from their central star. (ADAM BLOCK/MOUNT LEMMON SKYCENTER/UNIVERSITY OF ARIZONA (MAIN); ESA/HUBBLE & NASA ACKNOWLEDGEMENT: JUDY SCHMIDT (INSET))
A true planetary nebula then results, as the ionized gas emits, rather than reflects, light.
The Dumbbell Nebula, as imaged here through an 8″ amateur telescope, was the first planetary nebula ever discovered: by Charles Messier in 1764. the “double wedge” shape silhouetted against a spheroidal background is readily apparent through any modestly sized telescope, and makes one of the best targets for casual skywatchers. Unlike a preplantary nebula, a true planetary nebula is self-luminous, rather than being illuminated by reflected light. (MIKE DURKIN; MADMIKED/FLICKR)
The planetary nebula dissipates over ~20,000 years, with only the core — a white dwarf — remaining behind.
In the center of a planetary nebula, the core of a now-deceased Sun-like star heats up to temperatures exceeding ~30,000 K, leading to the ionization of the surrounding material, which causes it to emit its own light. After just 20,000 years or so, the planetary nebula will dissipate, leaving only a long-lived white dwarf behind. (NASA, ESA, AND C.R. O’DELL (VANDERBILT UNIVERSITY))
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.
