Relativistic disks by Appell-ring convolutions (2310.16669v2)

Abstract: We present a new method for generating the gravitational field of thin disks within the Weyl class of static and axially symmetric spacetimes. Such a gravitational field is described by two metric functions: one satisfies the Laplace equation and represents the gravitational potential, while the other is determined by line integration. We show how to obtain analytic thin-disk solutions by convolving a certain weight function -- an Abel transformation of the physical surface-density profile -- with the Appell-ring potential. We thus re-derive several known thin-disk solutions while, in some cases, completing the metric by explicitly computing the second metric function. Additionally, we obtain the total gravitational field of several superpositions of a disk with the Schwarzschild black hole. While the superposition problem is simple (linear) for the potential, it is mostly not such for the second metric function. However, in particular cases, both metric functions of the superposition can be found explicitly. Finally, we discuss a simpler procedure which yields the potentials of power-law-density disks we studied recently.