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A contracting mass of gas in a nebula that represents an early stage in the formation of a star, before nucleosynthesis has begun. Duration is around 100,000 years.

Stars in this stage fuse hydrogen into helium in their cores. About 90% of a star's life is spent in this stage, which for our Sun is about 10 billion years.

A star in this stage has exhausted the hydrogen in its core and begun to fuse helium into heavier elements. Duration ranges from a few million to 1 billion years.

A stage in which a star fuses helium into carbon and oxygen after the red giant phase. This stage lasts for about 100 million years.

An ejected envelope of ionized gas expelled by a red giant star, exposing the hot core which soon cools to form a white dwarf. Duration of the visible nebula is about 10,000 to 20,000 years.

A small, very dense star that is typically the size of a planet. Formed from the remnant core of a low to intermediate mass star, it slowly cools and fades over billions of years.