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arXiv · 2007.08823

The ISCO of charged particles in Reissner-Nordstr\"om, Kerr-Newman and Kerr-Sen spacetime

Kris Schroven·Saskia Grunau
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Abstract

In this article we study the innermost stable circular orbit (ISCO) of electrically charged particles in the electrically charged Reissner-Nordstr\"om 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-Nordstr\"om and Kerr-Newman spacetime for $qQ\geq 1$. 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 $qQ\geq 1+Q^2$ without dilaton-coupling and $qQ\geq 1+\frac{3}{2}Q^2$ with dilaton coupling $\alpha=1$.

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Kris Schroven, Saskia Grunau. 2020-07-17. The ISCO of charged particles in Reissner-Nordstr\"om, Kerr-Newman and Kerr-Sen spacetime. https://doi.org/10.1103/physrevd.103.024016

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