Starship Asterisk*

Abstract: We report results of a large set of N-body calculations aimed to study the evolution of multi-mass star clusters in external tidal fields. Our clusters start with the same initial mass-functions, but varying particle numbers, orbital types and density profiles. Our main focus is to study how the stellar mass-function and other cluster parameters change under the combined influence of stellar evolution, two-body relaxation and the external tidal field. We find that the lifetimes of star clusters moving on similar orbits scale as T sim T_RH^x, where T_RH is the relaxation time, and the exponent x depends on the initial concentration of the cluster and is around x approx 0.75. From the results for the lifetimes, we predict that between 53% to 67% of all galactic globular clusters will be destroyed within the next Hubble time. Low-mass stars are preferentially lost and the depletion is strong enough to turn initially increasing mass-functions into mass-functions which decrease towards the low-mass end. The details of this depletion are insensitive to the starting condition of the cluster. The preferential depletion of low-mass stars from star clusters leads to a decrease of their mass-to-light ratios except for a short period close to final dissolution. The fraction of compact remnants is increasing throughout the evolution and they are more strongly concentrated towards the cluster cores than main-sequence stars. For a sample of galactic globular clusters with well observed parameters, we find a correlation between the observed slope of the mass-function and the lifetimes predicted by us. It seems possible that galactic globular clusters started with a mass-function similar to what one observes for the average mass-function of the galactic disc and bulge. (Abridged)

kn5y wrote:Are the distances between stars in a globular cluster too small for the stars to have solar systems ?

Chris Peterson wrote:

kn5y wrote:Are the distances between stars in a globular cluster too small for the stars to have solar systems ?

For the most part, gravitational perturbations probably make it unlikely that many stars have planetary systems. When the stars were new they might have supported planetary systems for a few hundred million years, but most globulars contain old stars. Also, if you're considering solar systems similar to our own, it's worth remembering that most (but not all) globular clusters have very little material other than hydrogen and helium, and so you wouldn't expect terrestrial planets to form.

Abstract: We investigate the relationship between the mass of a globular cluster core and the sizes of its various stellar populations in a sample of 56 globular clusters. The number of core red giant branch stars is found to scale sub-linearly with core mass at the 3-$\sigma$ confidence level, whereas the relation is linear to within one standard deviation for main-sequence turn-off and sub-giant branch stars. We interpret our results as evidence for a surplus of red giant branch stars in the least massive cluster cores which is not seen for main-sequence turn-off and sub-giant branch stars. We explore various possibilities for the source of this discrepancy, discussing our results primarily in terms of the interplay between the cluster dynamics and stellar evolution.