A principle of corresponding states for two-component, self-gravitating fluids

نویسنده

  • R. Caimmi
چکیده

Macrogases are defined as two-component, large-scale celestial objects where the subsystems interact only via gravitation. The macrogas equation of state is formulated and compared to the van der Waals (VDW) equation of state for ordinary gases. By analogy, it is assumed that real macroisothermal curves in macrogases occur as real isothermal curves in ordinary gases, where a phase transition (vapourliquid observed in ordinary gases and gas-stars assumed in macrogases) takes place along a horisontal line in the macrovolume-macropressure (O / XV / Xp) plane. The intersections between real and theoretical (deduced from the equation of state) macroisothermal curves, makes two regions of equal surface as for ordinary gases obeying the VDW equation of state. A numerical algorithm is developed for determining the following points of a selected theoretical macroisothermal curve on the (O / XV / Xp) plane: the three intersections with the related real macroisothermal curve, and the two extremum points (one maximum and one minimum). Different kinds of macrogases are studied in detail: UU, where U density profiles are flat, to be conceived as a simple guidance case; HH, where H density profiles obey the Hernquist (1990) law, which satisfactorily fits to observed spheroidal components of galaxies; HN/NH, where N density profiles obey the Navarro-Frenk-White (1995, 1996, 1997) law, which satisfactorily fits to simulated nonbaryonic dark matter haloes. A different trend is shown by theoretical ∗Astronomy Department, Padua Univ., Vicolo Osservatorio 2, I-35122 Padova, Italy email: [email protected] fax: 39-049-8278212

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تاریخ انتشار 2009