What is a planetary nebula?

Question

Quizplus · Accepted Answer

A planetary nebula is the ejected envelope of a red giant surrounding a stellar core remnant. It is formed when the outer layers of a star are expelled into space as a result of nuclear fusion reactions that occur as the star runs out of fuel. The core of the star then collapses into a white dwarf, which emits ultraviolet radiation that causes the surrounding gas to glow brightly. Planetary nebulae often have a bipolar structure, with two lobes of material that are ejected in opposite directions. A planetary nebula is the ejected envelope, often bipolar, of a red giant surrounding a stellar core remnant.

What Is a Planetary Nebula