IAU Symposia

IAUS 312: Star Clusters and Black Holes in Galaxies across Cosmic Time

Start date/time

August 25, 2014

End date/time

August 29, 2014

Place

Beijing,
China, Nanjing

SOC Members:

Liu Fukun, Rainer Spurzem (co-chairs, China)
Joan Centrella (USA), Stefanie Komossa (Germany, China), Jufu Lu (Xiamen, China), Steve McMillan (Philadelphia, USA), Douglas Heggie (Edinburgh, UK), Luis Ho (KIAA/Carnegie), Giampaolo Piotto (Padova, Italy), Alison Sills (Canada), Joss Bland- Hawthorn (Australia), Hyung-Mok Lee (Korea), Ron Ekers (Australia), Martin Gaskell (Chile), Kim Venn (Canada)

LOC Members:

Liu Fukun (KIAA/DoA/PKU, co-chair), Rainer Spurzem (NAOC/KIAA/PKU, co-chair), Licai Deng (NAOC), Eric Peng (KIAA/DoA), Thijs Kouwenhoven (KIAA), Lijun Gou (NAOC), Qingjuan Yu (KIAA), Youjun Lu (NAOC), Lixin Li (KIAA), Peter Berczik (NAOC), Gareth Kennedy (NAOC), Luca Naso (NAOC), Yohai Meiron (KIAA), Maxwell Tsai (NAOC), Jifeng Liu (NAOC), Shuo Li (NAOC)

Topics

Black Holes in Galactic Nuclei, Galaxy Mergers and AGN Feedback, Dynamics of Stars and Gas around Black Holes, Accretion Disks, Galactic and Extrag. Globular Clusters, Nuclear Star Clusters, Dwarf Galaxies, Gravitational Wave Emission from Star Clusters and Galactic Nuclei, Gravitational Wave Instruments, Electromagnetic Counterparts of Gravitational Wave Emission.

Rationale

Star Clusters and Black Holes are moving into the focus of high-resolution astrophysics, computationally as well as observationally. For the first time cosmological models of galaxy formation in the universe reach down to the supermassive black holes forming and growing in the centers of galaxies by gas and star accretion. High star formation activity in the early universe leads to the formation of dense and very compact clusters of stars around them. Stars diffuse into the deep central potential and finally get disrupted by tidal forces of the central black holes or direct stellar collisions. After galaxy mergers gas settles in nuclear disks around supermassive black holes, which feed the central disk and jet engine of active galactic nuclei in the vicinity of the black holes. Relativistic dynamics of stars and gas is coupled to the larger galactic scales through energy and momentum feedback. Observations in many branches of the electromagnetic spectrum are for the first time converging with theoretical modeling and computer simulations. This symposium will bring together experts in high resolution observational data as well as theoretical modeling, in cluster stellar populations and cluster modeling - related to dynamical processes involving dense stellar systems, central gas in active and quiescent galactic nuclei, and black holes, across all wavelengths and instruments.

The physics of galactic nuclei gets even more challenging in the case of galaxy mergers; after major mergers gas and stars are rapidly transported towards the central region and a bound supermassive black hole binary may form. Its subsequent evolution is determined by interactions with stars and gas, and ultimately gravitational radiation emission, during spiral-in and final relativistic coalescence. Electromagnetic counterparts of gravitational wave emission from relativistic spiral-in and coalescence of black holes are highly sought after, in order to identify astrophysical sources of gravitational waves and provide independent evidence. Recently it became clear that strong recoils can occur, depending on the original spins of the black holes. This leads to excursions of supermassive black holes with all their counterparts (AGN, hypercompact stellar system, tidal disruptions of stars with X-ray flares, relativistic inspiral of stellar mass black holes) into the outer halos of galaxies or even - if there are superkicks - into intergalactic space. This symposium will cover the astrophysical determinants of black hole spins, and the evolution of binary black holes in gas-poor and gas-rich mergers, their final spins, recoils and possible ejections from galaxies. Star clusters across cosmic time are also to be found in the outskirts of galaxies - at the lower mass end of the galaxy - black hole correlations. They are formed directly during mergers and strong star formation episodes, presumably in low mass systems with little, if any, dark matter. However the most massive star clusters seem to form a continuous link with the nuclei of ultra compact dwarf galaxies. Modeling of cluster formation and long-term evolution of globular and open star clusters has long been highly influenced by our nearby hundred or so globular clusters in the Milky Way. In recent years this local sample has been complemented by many more globular clusters around Local Group galaxies, which can still be observed star-by-star. But some external galaxies exhibit systems of thousands of globular clusters, whose formation is most likely triggered by galaxy merging, and recently a huge amount of free floating globular clusters has been found by the Hubble Space Telescope between galaxies in the Virgo cluster. Our conventional approach of inverse dynamical synthesis of globular cluster formation needs update and improvement with respect to the wealth of new data coming in about extragalactic, extra-local-group globular clusters. Our planned symposium shall be the focal point to exchange first results in this direction as well as to discuss future research.

Last, but not least, everything is NOT everything understood even in the small sample of our galactic globular clusters. Recent high resolution observations show that clusters often show complex phenomena like multiple stellar populations and particular patterns in their giant branch in the Hertzsprung-Russell diagram. We are beginning to explore these features by theoretical modeling, and first results hint towards two dynamically distinct phases of star formation in clusters, with complex chemical evolution. Also the mass loss history of star clusters and their tidal arm features are clues to the structure of the galactic halos they live in. Long term dynamical evolution of realistic globular star clusters with binaries, multiple populations, initial rotation and realistic tidal external fields are also far from being completed. Their stellar populations develop compact objects such as white dwarfs, neutron stars, stellar mass black holes and binaries composed of these objects. These binaries are promising sources of gravitational waves detectable by ground-based instruments.

Star clusters and black holes, galaxy mergers, star and cluster formation, stellar populations, high resolution observations of star clusters and galaxies across all redshifts including those containing black holes and gas are the common topic of all these timely and actively growing subjects as described above. Physical processes and computational methods have significant overlap across all objects covered here, the common theme being the black holes and their astrophysical environment. Novel instrumentation and simulation techniques may be also admitted as belonging to this symposium proposal as long as they have a direct impact on the scientific subjects here.