Caterina Chiari | Searcharxiv

arXiv2024

Dynamical friction in the quasi-linear formulation of modified Newtonian dynamics (QuMOND)

Aims. We explore the dynamical friction on a test mass in gravitational systems in the Quasi linear formulation of Modified Newtonian Dynamics (QuMOND). Methods. Exploiting the quasi linearity of QuMOND we derive a simple expression for the dynamical friction in akin to its Newtonian counterpart in the standard Chandrasekhar derivation. Moreover, adopting a mean field approach based on the Liouville equation we obtain a more rigorous (though in integral form) dynamical friction formula that can be evaluated numerically for a given choice of the QuMOND interpolation function. Results. Consistently with previous work, we observe that dynamical friction is stronger in MOND with respect to a baryon only Newtonian system with the same mass distribution. This amounts to a correction of the Coulomb logarithmic factor via extra terms proportional to the MOND radius of the system. Moreover, with the aid of simple numerical experiments we confirm our theoretical predictions and those of previous work on MOND.

astro-ph.GA↗

arXiv2023

Relativistic dynamical friction in stellar systems

We extend the classical formulation of the dynamical friction effect on a test star by Chandrasekhar to the case of relativistic velocities and velocity distributions also accounting for post-Newtonian corrections to the gravitational force. The original kinetic framework is revised and used to construct a special-relativistic dynamical friction formula where the relative velocities changes in subsequent encounters are added up with Lorentz transformation and the velocity distribution of the field stars accounts for relativistic velocities. Furthermore, a simple expression is obtained for systems where the post-Newtonian correction on the gravitational forces become relevant even at non-relativistic particle velocities. Finally, using a linearized Lagrangian we derive another expression for the dynamical friction expression in a more compact form than that of Lee (1969). Comparing our formulation with the classical one, we observe that a given test particle suffers a slightly stronger drag when moving through a distribution of field stars with relativistic velocity distribution. Vice versa, a purely classical treatment of a system where post-Newtonian (PN) corrections should be included, over estimates the effect of dynamical friction at low test particle velocity, regardless of the form of velocity distribution. Finally, a first order PN dynamical friction covariant formulation is less strong than its classical counterpart at small velocities but much higher for large velocities over a broad range of mass ratios

astro-ph.GA↗