For some stars, their last act is a final exhalation of gases, which we call a planetary nebula. While a living being’s last breath is closely followed by death, a star can continue to shine. And that shining illuminates the final exhalation of gases like a cosmic, diaphanous veil.
Astronomers have captured one such planetary nebula in this stunning image. This brightly-lit, stellar exhalation will last only 10,000 years, a brief moment in astronomical terms. As the last breath expands and travels away from the star that exhaled it, it will become diffuse and will no longer be visible. All that will be left is the tiny and intensely hot remnant of the star that spawned it.
Astronomers with the European Southern Observatory’s (ESO) Very Large Telescope (VLT) captured this image of planetary nebula ESO 577-24 as part of the ESO Cosmic Gems Programme. That programme produces images of objects that are interesting, visually stunning, or otherwise intriguing, as a part of their public outreach efforts.
Before this star took its final breath, it was a red giant, a huge type of star that has exhausted the hydrogen in its core. Eventually, fusion moved to the vast shell of expanding gas that surrounds the core. The star expanded, and as the outer shell cooled, it dimmed to a reddish-orange glow.
This star spent about a billion years as a red giant, and once that phase of its life ended, it shed its outer layers in a last exhalation, which astronomers call a stellar wind. Then it turns into a white dwarf. The image at the top captures the star when it shed its outer layers, forming a planetary nebula and leaving a white dwarf behind.
Planetary nebula is a misnomer from history. In the earlier days of astronomy, when telescopes were not so powerful as today, these shells of expanding gas resembled planets. We now know that they have nothing to do with planets, and everything to do with stars, but the name has stuck.
As for the star at the center of the image, its fate is sealed. All fusion has ceased, and the only energy escaping it is thermal. A white dwarf is also called a degenerate dwarf, because it’s hardly a star at all anymore. It has degenerated into a stellar remnant. It will spend an eternity as an extremely dense object, with as much mass as our Sun, but occupying only as much space as Earth.
The expanding shell of gas has a different fate. No one can say exactly when, but at some point in the future, the gas will be swept up in the formation of another solar system. Some of it will form part of a star, or maybe a binary pair of stars, in that far-off future. Some of it may be formed into planets.
There’s also an infinitesimally small chance that some of it will become part of a living being. Imagine that.