The Egg Nebula: Hubble's View of a Dying Star's Searchlight Beams

A brief stage at the end of a star's life

The NASA/ESA Hubble Space Telescope has led research into what happens to stars like the Sun as they die. As such a star runs out of nuclear fuel, it passes through a preplanetary (or protoplanetary) nebula stage — despite the name, nothing to do with planets. This Hubble image of the Egg Nebula, released by NASA on April 27, 2012, is one of the best views yet of that short, dramatic phase.

Why so few are known

Over a few thousand years, the hot remains of the aging star at the center heat the surrounding gas, excite it and make it glow — turning the object into a planetary nebula. Because the preplanetary stage is so brief, few exist at any one time, and they are very faint, needing powerful telescopes to see. Rare and dim, they were found only comparatively recently: the Egg Nebula, the first one discovered, had been found less than 40 years before this image appeared, and much about the class is still unknown.

What the image shows

• The hidden star. At the center, buried in a thick cloud of dust, is the nebula's central star. It cannot be seen directly.
• Four searchlight beams. Light from the star shines out through the nebula in four beams. The leading idea is that ring-shaped holes in the dusty cocoon, carved by jets from the star, let the light escape the otherwise opaque cloud. Exactly how jets make these holes is not known; one possibility is that a binary star, not a single star, sits at the center.
• Onion-like shells. The fainter cloud around the cocoon is layered like an onion, built by periodic bursts of material thrown off by the dying star — typically every few hundred years.

How far, how big

The distance is known only very roughly: the best estimate is about 3,000 light-years from Earth. So the nebula's true size is uncertain too — it could be larger and farther away, or smaller and nearer.

The image combines exposures in visible and infrared light from Hubble's Wide Field Camera 3.

Sources

Based on "Hubble Images Searchlight Beams from a Preplanetary Nebula," NASA image release of April 27, 2012, NASA Image and Video Library; NASA material, not copyrighted and in the public domain. Image credit: ESA/Hubble and NASA, used under the Creative Commons Attribution 4.0 licence.