Dynamical Evolution Of The Milky Way Planet-like Clusters

Given the initial conditions including (1) number density distribution in space which has the similar form to the present day ones, (2) both the power law and Gaussian mass functions for clusters, and (3) two different velocity distributions which one has a constant dispersion and the other is described by the Eddington formula, the dynamical evolution of globular clusters in our Milky Way Galaxy is investigated in detail by means of Monte Carlo simulations. Four dynamic mechanisms in the present paper are considered. They are the stellar evaporation in the tidal field, the stellar evolution during the early evolutionary stage, the tidal shocks due to clusters passing through the bulge and disk, and the dynamical friction. The evolution time in our calculation is chosen to be 12 Gyr, which is the mean value of globular cluster ages in the Galaxy. For the Galaxy, a model contained three components (bulge, disk and halo) suggested by Paczynski(1990) is adopted, which can reproduce most of the global observational properties of the Milky Way such as the rotation curve.Comparing with the current observations, which include the number density distribution in space, mass function, etc., the so-called standard modes for both the power law and Gaussian cluster initial mass functions are selected among many runs of simulations. The deviation from the standard modes, which is resulted from the change of the parameter for the initial conditions, is discussed in detail. The discussion of the model parameters is also presented although they are adopted as the typical values based on previous work.Based on our simulations, some relevant discussions about the mass contributions to the Galactic central region and stars in the halo due to the dynamic evolution of globular clusters are also qualitatively presented. Followings are the main conclusions of this thesis.1. For the four dynamic processes, it is found that stellar evaporation is very important for clusters with low masses and the other three are all important for massive ones;2. Both the power law and Gaussin initial clusters mass functions willreach the observed Gaussian form of the present-day mass function after several giga years of dynamic evolution. The main feature of the mass function will unchange during the further evolution;3. The dispersion of the observed globular cluster mass function mainly depends on the adopted model of the host galaxy;4. The number density distribution of globular cluster in space will change with time due to the dynamic evolution, especially for those in the central region of the Galaxy;5. For the power law initial cluster mass function, the peak value of the mass function after the dynamic evolution is sensitive to the lower limit of the initial mass function we adopt. The suggested value in this paper is - 104M, which is consistent with that reduced from the dynamical analyses for the giant molecular clouds.6. The change of the power index for the initial mass function will influence the peak value mentioned in the last item. The suggested value is between 1.5 and 2 which is consistent with the recent observations in starburst galaxies;7. The mass contribution to the Galactic central region (Galactocentric distance R < 0.1 kpc) and the central black hole due to globular clusters dissented into the central region is significant;8. Only several percent of the halo stars were original from globular clusters. The formation efficiency of the globular clusters is very low comparing with the total baryon mass in the Galaxy.