What causes interstellar dust and gas to start to contract and form a protostar?

Interstellar dust and gas start to contract and form a protostar due to the presence of gravitational force. As a protastar begins to condense from dust and gas clouds, it emits infrared light and these single stars fragment into smaller objects forming many stars at one time.

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the principles and empirical processes of discovery and demonstration considered characteristic of or necessary for scientific investigation, generally involving the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to test the hypothesis, and development of a conclusion that confirms, rejects, or modifies the hypothesis.