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.
Like all Sun-like stars, it will leave a white dwarf/planetary nebula combination behind.
However, there’s a unique phase preceding that final transition: a preplanetary nebula.
In the final stages of a red giant star’s life, its core runs out of fusible helium.
The star pulses internally, fusing hydrogen in a shell surrounding the core.
These fusion bursts eject the diffuse star’s outer, hydrogen gas layers.
The central star’s light reflects off the surrounding cool, dark gas.
This marks the beginning of the star’s final phase: a preplanetary (or protoplanetary) nebula.
The remaining surrounding gas evolves from a spherical to an axial shape.
The star quickly develops fast-moving, collimated winds, creating a “bipolar” nebula.
Gas molecules collide, creating knots and shocks, visible in high-resolution photographs.
All the while, the central core contracts and heats up.
When the gas is exhausted and the core reaches ~30,000 K, the nebulous material finally ionizes.
A true planetary nebula then results, as the ionized gas emits, rather than reflects, light.
The planetary nebula dissipates over ~20,000 years, with only the core — a white dwarf — remaining behind.
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.
Starts With A Bang is written by Ethan Siegel, Ph.D., author of Beyond The Galaxy, and Treknology: The Science of Star Trek from Tricorders to Warp Drive.