Chandrasekhar's Dynamical Friction and non-extensive statistics
  The motion of a point like object of mass $M$ passing through the background
potential of massive collisionless particles ($m << M$) suffers a steady
deceleration named dynamical friction. In his classical work, Chandrasekhar
assumed a Maxwellian velocity distribution in the halo and neglected the self
gravity of the wake induced by the gravitational focusing of the mass $M$. In
this paper, by relaxing the validity of the Maxwellian distribution due to the
presence of long range forces, we derive an analytical formula for the
dynamical friction in the context of the $q$-nonextensive kinetic theory. In
the extensive limiting case ($q = 1$), the classical Gaussian Chandrasekhar
result is recovered. As an application, the dynamical friction timescale for
Globular Clusters spiraling to the galactic center is explicitly obtained. Our
results suggest that the problem concerning the large timescale as derived by
numerical $N$-body simulations or semi-analytical models can be understood as a
departure from the standard extensive Maxwellian regime as measured by the
Tsallis nonextensive $q$-parameter.
