Which event takes place first in the stages before the birth of a star

Nebulae are clouds of gas that have high density. It condenses into a large globule of gas and dust, and begin to heat up and glow as the gas particles run into each other. Nuclear reactions occur as hydrogen fuses and forms helium. Strong winds are also produced, pushing the molecules and gas surrounding the forming star. Solid shape is then achieved as hydrostatic equilibrium is attained.

Main sequence stars will then continue to expand into red giant.

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answer: Gravity pulls gas and dust together.