Ambipolar-diffusion Timescale, Star-formation Timescale, and the Ages of Molecular Clouds: Is There a Discrepancy ?

We re-examine 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 pre-stellar cores. We show that all available observational data are consistent with lifetimes of molecular clouds comparable to ≈ 10 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. Subject headings: accretion – IS dust – magnetic fields – MHD – molecular clouds: ages – star formation