Q&A: Normal Stars, White Dwarf Stars, and Star Clusters

Q:
I wanted to know the difference between a white dwarf and neutron star, and the meaning of planetary nebula and nebula.

A:
A nebula refers to clouds of dust and gas that lie between stars, in so-called interstellar space. A planetary nebula is a special type of nebula made when the outer layers of an old, giant star are thrown off into space. A white dwarf is the small, faint and very dense star that remains behind after a planetary nebula has formed. Stars with masses that are no more than about 8 times as massive as the Sun should form planetary nebulae and white dwarfs. More massive stars collapse down onto themselves in spectacular events known as supernova explosions. What's left behind is a tiny star called a neutron star that's much more dense than a white dwarf.

More information on White Dwarfs & Planetary Nebulas.