Self-force as probe of internal structure

Understand

The self-force acting on a (scalar or electric) charge held in place outside a massive body contains information about the body's composition, and can therefore be used as a probe of internal structure.

• We explore this theme by computing the (scalar or electromagnetic) self-force when the body is a spherical ball of perfect fluid in hydrostatic equilibrium, under the assumption that its rest-mass density and pressure are related by a polytropic equation of state.
• The body is strongly self-gravitating, and all computations are performed in exact general relativity.
• The dependence on internal structure is best revealed by expanding the self-force in powers of 1/r, with r denoting the radial position of the charge outside the body.