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whooo_me t1_jaimfai wrote

If nebulae are composed (at least partially) of gas, wouldn't that gas just expand outwards in a vacuum and disperse?

Is there some gravitational source retaining the gas?

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MadMeadyRevenge t1_jaj38k4 wrote

Every single point of mass has a gravitational field, including tiny elemental particles such as protons or neutrons. The force of attraction between two masses is governed by Newton's law of gravitation, such that larger masses attract smaller ones and mass begins to gather in small pockets, "it's getting closer together" and then, eventually, "it's a star!"

TLDR: Yes, the gases themselves are gravitational sources.

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