a. 10–100 million years is the answer.
Solar mass stars are thought to accrete rapidly. Premain sequence solar mass protostars are probably formed by the collapse of part of a molecular cloud into the "cloud core" in about 105 years (Hartmann, 2000). Strong outflows and jets are sometimes observed.
Star formation begins with the collapse of molecular clouds and fragmentation into highly dense masses. These masses initially contain about 0.01 solar masses, but increase in mass as the surrounding matter is collected by accretion.
Protostars are very young stars, still collecting mass from their original molecular clouds. The protostar stage is the earliest in the process of stellar evolution.
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