Quote:
Originally Posted by sjastro
If core collapse results in a segregation of mass, a process known as evaporation occurs where the lighter mass stars have sufficent kinetic energy to escape the cluster. This is an on going process which results in globulars and open clusters having finite life spans.
Steven
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Steven,
This is a great topic of debate. I wonder if anyone else with some ideas can add to it.
The scenarios you've painted are quite feasible and I've read your points with much interest. A globular cluster is a fascinating but by no means simple system; witness the complexity of n-body problems. And I certainly agree with you that globular and open clusters have finite life spans. Eventually globular clusters as well as the host galaxy will collapse as their elements lose their rotational energy. The outer stars may well be lost to space, whether by evaporation or being stripped by other massive bodies nearby.
However, globular clusters remain gravitationally bound for a very long time, maybe 10 billion years and more. We cannot even say how many, if any, have ceased to exist.
I think the question is why clusters don't collapse much sooner but appear to be, more or less, in equilibrium. I made the point about the rotational energy of the cluster as a whole. Maybe we can also think of a globular cluster as an enormous multiple star system with each star following some complex trajectory within the cluster (elliptical, figure eight etc). Eventually, as the heavier stars congregate to the center through energy re-distribution, the scenario you've painted might kick in. As far as I know, no black holes have been established in any globular cluster yet, not even 47 Tuc. Proposed maybe, but may indeed not be.
Regards, Rob.