STARDISK is the joint project between Fesenkov Astrophysical Institute (Almaty) and Astronomisches Rechen-Institut (Heidelberg). The project is sponsored by the Volkswagen Foundation. It aims at the numerical researches of active galactic nuclei as multicomponent system composed of compact stellar cluster, gaseous accretion disk and the black hole. Supermassive black holes are located in most if not all centres of galaxies, including our own. Their growth due to interaction with and accretion of surrounding gas and stars is one of the most interesting and important fields in astrophysics nowadays. New space and ground based telescopes of present (Hubble Space Telescope, VLT, Chandra, XMM Newton) and future generations (Next Generation Space Telescope) provide a large amount of new high-resolution data on morphology and kinematics of stellar and gaseous systems near black holes. Since the underlying equations are very complex, theory consists of computer simulations in which the evolution of stars (gravitating mass points) with a central potential (black hole) and a gaseous disk is followed by direct modelling of stellar orbits. The project examines a special topic in this area, namely the interplay between stellar dynamical two-body relaxation and star-gas interactions due to a central accretion disk.
To facilitate direct N-body simulations this project relies on special purpose hardware equipment like GRAPE and more recently Nvidia Tesla cards which, together with standard computers, provides an extremely competitive computing systems for direct N-body simulations, with very good price-performance ratio. Both GRAPE and GPU cards are also used to equip computer clusters so parallelisation of the task further speeds up the calculations. To employ massively parallel computing on special hardware for direct integration of dense stellar systems the two N-body codes have been used NBODY6++ (based on the family of codes developed by S.Aarseth) and phiGRAPE/GPU.
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| GRAPE6 BL4 (without heat sink) | Tesla C1060 |
The project resulted in the creation of a small computer cluster at Fesenkov Astrophysical Institute, and also led to internships of young researchers at Astronomisches Rechen-Institut (Heidelberg) where they got experience with high performance computing and with N-body codes.
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| Mini GRAPE-cluster: 2 Xeon-nodes with GRAPE6-BL4 cards |
Xeon-node with 4 Tesla C1060 cards |
The main finding of the project is that an accretion disk can indeed decelerate stars and thus enhance the accurate rate onto the black hole. This and some other results have been published in peer reviewed journals.
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| Supermassive black hole growth with (upper thick lines) and without (lower thin lines) dissipative force for specific accretion radius racc = 0.04 |
