Abstract
We discuss the possibility to analyze the problem of gravothermal catastrophe in a new way, by obtaining thermodynamical equations to apply to a selfgravitating system. By using the King distribution function in the framework of statistical mechanics we treat the globular clusters evolution as a sequence of quasi-equilibrium thermodynamical states.
Highlights
Globular clusters (GCs) are stellar systems with masses within the interval 104 − 106 M, containing a number of stars of the order of 105. They are considered as nearly spherical systems due to their low values of eccentricity e; at least 50% of GCs have e < 0.1 and there are no clusters with e > 0.2
The core radius rc, namely the radial coordinate at which the brightness becomes one half of the corresponding value at the center of the system, is almost 10 pc, whereas the tidal radius rt, which is the biggest spatial extension of the cluster allowed by the external tidal field, is typically around 50 pc. For their symmetry and age, there is the possibility to test the evolution of a GCs studying a classical single mass King model (King, 1966) in relation to thermodynamical instability phenomena
It is important to note that while the equilibrium is given by the form of the distribution which depends on the Fokker-Planck equation and consider the real nature of collisions, thermodynamics plays a role in the tidal effects acting on the confination of the system, due to a two competitive phenomena: one given by stellar encounters which tend to refresh the tail of high velocities in the distribution and one due to evaporation of stars which prevents the formation of it, maintaining the system in a sort of thermodynamical equilibrium with the same distribution function even if in presence of a cutoff in the velocity of the stars
Summary
Globular clusters (GCs) are stellar systems with masses within the interval 104 − 106 M , containing a number of stars of the order of 105. The core radius rc, namely the radial coordinate at which the brightness becomes one half of the corresponding value at the center of the system, is almost 10 pc, whereas the tidal radius rt, which is the biggest spatial extension of the cluster allowed by the external tidal field, is typically around 50 pc For their symmetry and age, there is the possibility to test the evolution of a GCs studying a classical single mass King model (King, 1966) in relation to thermodynamical instability phenomena. It is important to note that while the equilibrium is given by the form of the distribution which depends on the Fokker-Planck equation and consider the real nature of collisions, thermodynamics plays a role in the tidal effects acting on the confination of the system, due to a two competitive phenomena: one given by stellar encounters which tend to refresh the tail of high velocities in the distribution and one due to evaporation of stars which prevents the formation of it, maintaining the system in a sort of thermodynamical equilibrium with the same distribution function even if in presence of a cutoff in the velocity of the stars
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