P4_6 Orbiting a Black Hole

Abstract

During the BBC's classic science fiction show Doctor Who, the Doctor and his assistant Rose land the TARDIS on a planet that is orbiting a black hole - an 'impossible situation' according to the Doctor. This paper calculates the minimum radius and required angular momentum of the closest stable circular orbit around a Schwarzschild black hole of comparable mass to the one at the centre of the Milky Way (named Sagittarius A*). The minimum radius is found to be 3.54x10¹⁰m while the angular momentum required to sustain this orbit is 2.04 x10¹⁰m²s^-1kg^-1.