The ISCO of charged particles in Reissner-Nordström, Kerr-Newman and Kerr-Sen spacetime

Abstract

In this article we study the innermost stable circular orbit (ISCO) of electrically charged particles in the electrically charged Reissner-Nordström spacetime, the Kerr-Newman spacetime and the Kerr-Sen spacetime. We find that the radius of the ISCO increases with an increasing particle-black hole charge product $|qQ|$ in the case of attractive Coulomb interaction $qQ<0$. For repulsive Coulomb interaction, the ISCO radius first decreases to a minimum and then increases again, until it diverges as the charge product approaches one. If the charge $Q$ of the black hole is very small, the minimum of the ISCO radius lies at $qQ=0$. Repulsive and attractive Coulomb interactions will always increase the ISCO radius in this limit. Stable bound orbits of charged particles cease to exist in the Reissner-Nordström and Kerr-Newman spacetime for $qQ\ge 1$. In the Kerr-Sen spacetime the limiting case depends on the charge of the black hole and if dilaton coupling is applied to the test particle. We find $qQ\ge 1+Q^2$ without dilaton-coupling and $qQ\ge 1+\frac{3}{2}{Q}^2$ with dilaton coupling $\alpha =1$.

16 pages, 8 figures

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• First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
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• Dynamics of charged particles moving around Kerr black hole with inductive charge and external magnetic field
• Periodic orbits of neutral test particles in Reissner-Nordström naked singularities
• Internal structures and circular orbits for test particles
• Innermost stable circular orbits around a Reissner-Nordström-global monopole spacetime in a homogeneous magnetic field