What is a planetary nebula?
A) a disk of gas surrounding a protostar that may form into planets
B) what is left of its planets after a low-mass star has ended its life
C) the expanding shell of gas that is no longer gravitationally bound to the remnant of a low-mass star
D) the molecular cloud from which protostars form
E) the expanding shell of gas that is left when a white dwarf explodes as a supernova

Question

Quizplus · Accepted Answer

A planetary nebula is the expanding shell of gas that is no longer gravitationally bound to the remnant of a low-mass star. It is formed when such a star exhausts its nuclear fuel and sheds its outer layers, which ionize and glow due to the intense radiation from the hot core. The resulting nebula is often a colorful and intricate structure that lasts for a few tens of thousands of years before dispersing into the interstellar medium. The name "planetary" comes from the mistaken belief of early astronomers that these objects resembled the disks of Uranus or Neptune, but they have no connection to planets or exoplanets.

What Is a Planetary Nebula