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Dynamical friction and MONDFernando J. Selman

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The roads to dynamical

friction

Binary collision approximation Chandrasekhar 1942, 1943

Chandrasekhar fluctuating force arguments Uhlenbeck and Ornstein 1930 (non stellar) Chandrasekhar and von Neumann 1943 Ahmad and Cohen (1974) Kandrup (1980) Bekenstein and Maoz (1992) del Popolo (1996)o Colpi and Pallavicini (1998)o Nelson and Tremaine (1999)

Polarization cloud methodo Marochnik (1968)o Kalnajs (1972)o Lynden-Bell and Kalnajs (1972)o Tremaine and Weinberg (1984)o Bekenstein and Zamir (1990)

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The approximations

Binary collisions Local approximation: infinite and homogeneous system Markov approximation: binary collisions of negligible duration Diffusion approximation: diffusion described by a Fokker-Planck

equation Neglect of self-gravity of response Resonances

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Chandrasekhar Binary Collisions

Formula

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Statistics of the fluctuating field

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Polarization cloud method

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The frictional drag formulas

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Caveat: M=10^5Msun, V = 100km/s, 20pc x 30pc