Gravothermal catastrophe in anisotropic spherical systems |
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| Authors: | Manuela Magliocchetti Giuseppe Pucacco & Enrico Vesperini |
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| Institution: | Institute of Astronomy, Madingley Road, Cambridge CB3 0HA,;Department of Physics, Universitàdi Roma 'Tor Vergata', Via della Ricerca Scientifica 1, I-00133 Roma, Italy,;Department of Physics and Astronomy, University of Massachusetts, Amherst, 01003 MA, USA |
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| Abstract: | In this paper we investigate the gravothermal instability of spherical stellar systems endowed with a radially anisotropic velocity distribution. We focus our attention on the effects of anisotropy on the conditions for the onset of instability and in particular we study the dependence of the spatial structure of critical models on the amount of anisotropy present in a system. The investigation has been carried out by the method of linear series which has already been used in the past to study the gravothermal instability of isotropic systems._ We consider models described by King, Wilson and Woolley–Dickens distribution functions. In the case of King and Woolley–Dickens models, our results show that, for quite a wide range of the amount of anisotropy in the system, the critical value of the concentration of the system (defined as the ratio of the tidal to the King core radius of the system) is approximately constant and equal to the corresponding value for isotropic systems. Only for very anisotropic systems does the critical value of the concentration start to change and it decreases significantly as the anisotropy increases and penetrates the inner parts of the system. For Wilson models the decrease of the concentration of critical models is preceded by an intermediate regime in which critical concentration increases, reaches a maximum and then starts to decrease. The critical value of the central potential always decreases as the anisotropy increases. |
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| Keywords: | celestial mechanics stellar dynamics globular clusters: general |
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