Star clusters in the solar Neighbourhood: how are they destroyed?

Abstract

We predict the survival time of initially bound star clusters in the solar neighbourhood taking into account: (1) stellar evolution, (2) tidal stripping, (3) shocking by spiral arms and (4) encounters with giant molecular clouds. We find that the predicted dissolution time is tdis = 1.7(Mi/104 M )0.67 Gyr for clusters in the mass range of 102 <Mi <105 M . The resulting predicted shape of the logarithmic age distribution agrees very well with the empirical one, derived from a complete sample of clusters in the solar neighbourhood within 600 pc. The required scaling factor implies a star formation rate of 4 × 102 M Myr−1 within 600 pc from the Sun or a surface formation rate of 3.5 × 10−10 M yr−1 pc−2 for stars in bound clusters with an initial mass in the range of 102 to 3 × 104 M .