M2 Globular Cluster NGC7052 Galactic Nucleus M16 Open Cluster
Globular Clusters Galactic Nuclei Open Clusters
JD11- IAU 2003
Dynamics and Evolution
of Dense Stellar Systems
Sydney, Australia, 18 July 2003

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In the main bodies of galaxies, the timescale for individual gravitational encounters of stars to significantly alter an orbit (the relaxation time) and the timescale for a physical collision between two stars (the collision time), are both much longer than the age of the universe. In three kinds of stellar systems, globular clusters, galactic nuclei, and young, star-forming regions, these timescales can be short compared to the lifetimes or ages of the systems. The unifying theme of our proposed symposium is the investigation of systems with this property.

While the subject of dynamics of globular clusters is thoroughly studied, the other two kinds of systems have rather different dimensionless numbers (the ratio of collision to relaxation time, the gas fraction, and the total number of stars). The results from globular clusters can only partially be carried over to the other systems, which are far less well understood.

At the same time, there are a host of new observational results, in multiple wavelengths, which address various aspects of these problems. There are several crosscutting themes that are heavily observational.

One crosscutting theme is multiwavelength observations. For example, in the galactic center we have a star cluster as dense as a globular which contains young stars that must have formed in situ. The galactic center is observed from Gamma-rays, infra-red and radiofrequencies.

A second crosscutting theme is the formation of supermassive black holes. X-ray observations suggest the presence of intermediate mass (103 solar mass) BH in star-forming regions in nearby galaxies that can not be produced by the death of individual stars. They may, however, be produced in star forming regions or by runaway mergers in globular or galactic-center clusters. At the same time, AGN observations at multiple wavelengths probe the growth of black holes at moderate redshift, and could be confronted with the Lyman dropout objects observed in the (rest frame) ultraviolet by, eg, Steidel and Adelberger. What is the implication of the paucity of AGN in these objects, which must surely be forming - or recently formed bulges? This result is in sharp contrast to the ubiquity of supermassive BH in galactic nuclei at the present epoch. X-ray emission is traditionally seen as the marker of black hole accretion. Are any of these sources X-ray emitters?

A third crosscutting theme is cosmogony - how do these things form. For each of five kinds of objects (stars, black holes, globular clusters, young stellar clusters and galactic nuclei) we will be interested in exploring formation processes.

The attack on these systems relies on massive computational systems and special purpose computers for theory, and on optical, infrared and X-ray telescopes for observations. The Hubble Space Telescope is contributing new data. The Sydney meeting is well-timed for an infusion of results from Chandra. There is a possibility of first results from SIRTF.

There is also considerable theory being done on gravitational waves from degenerate stars or binaries in anticipation of LIGO results. LIGO and especially LISA offer considerable prospect of opening the "gravitational wave window" on these sources. The clearest contact point is the galactic nuclei and formation of black holes, which will be brilliant LISA sources, however, the interaction of degenerate objects in dense systems, even in globular clusters, offer a rich variety of topics. For example, the LISA low-frequency background will be provided largely by degenerate binaries in the local group, many of which (perhaps most) will be in dense stellar systems. In these subjects we hope to draw the gravitational wave community to our meeting.

The first meeting on "Dense Stellar Systems" occurred in Toronto in 1988. There have been two others since, at Santa Barbara in 1993 and at Rutgers in 1998. They were devoted essentially to theory. In this meeting, we expect to develop more the observational point of view.

  1. Globular Clusters
    • How do they form?
    • The possible presence of 103 Msun black holes.
    • The evolution of systems with black holes and neutron star binaries.
    • Environmental influence, mass loss and disruption.
    • Theory and observations of primordial binaries.
    • Physical collisions -- formation of peculiar objects like blue stragglers
  2. Galactic Nuclei
    • Are supermassive black holes ubiquitous?
    • Why are some nuclei gas rich and others clean as a whistle?
    • How do galactic nuclei form and evolve, eg in nucleated dwarfs?
    • How do nuclei evolve - how is this different from globular clusters?
    • What happens when galactic nuclei merge?
    • What processes determine the morphology and dynamics of galactic centers.
    • What do nuclei look like at z~3?
  3. Young stellar clusters
    • Connecting small scale to galactic star formations
    • How do stellar interactions/coagulation influence the IMF?
    • How do they influence planet formation?
    • How do clusters evolve, eg how do they survive in the face of supernova and mass ejection? how do they lose their substructure and become round?
    • How are the heaviest stars and possible 103 solar mass black holes made?
    • How do star clusters form in violent environments like merging galaxies and in more quiescent ones like the galactic disk? How do they form in our galactic center?
    • Young star clusters as progenitors of globular clusters.

Scientific Organizing Committee

Questions to: francoise.combes@obspm.fr