Ambipolar-diffusion timescale, star formation timescale, and the ages of molecular clouds: Is there a discrepancy?

We reexamine critically the estimates of the duration of different phases of star formation and the lifetimes of molecular clouds based on the ages of T Tauri stars, age spreads of stars in clusters, and statistics of prestellar cores. We show that all available observational data are consistent with lifetimes of molecular clouds comparable to ∼10⁷ yr, as well as with the predictions of the theory of self-initiated, ambipolar-diffusion-controlled star formation. We conclude that there exists no observational support for either "young" molecular clouds or "rapid" star formation.