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arXiv · 2304.04313

Conservative limits on the electric charge of Sgr A* in the Reissner-Nordstrom metric

Ruchi Mishra·Ronaldo S. S. Vieira·Włodek Kluźniak
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Abstract

In general relativity, the gravitational field of an electrically charged, non-rotating, spherically symmetric body is described by the Reissner-Nordstr\"om (RN) metric. Depending on the charge to mass ratio, the solution describes a black hole or a naked singularity. In the naked-singularity regime, a general property of this metric is the existence of a radius, known as the zero-gravity radius, where a test particle would remain at rest. As a consequence of repulsive gravity there is no circular orbit inside this radius, and at least a part of any quasi-stable structure must necessarily lie outside of it. Assuming the iconic torus in the compact source Sgr A* at the Galactic center observed by the Event Horizon Telescope (EHT) to be the image of a quasi-stationary fluid structure, we provide rigorous constraints in the RN metric on the electric charge-to-mass ratio Q/M of Sgr A*. A comparison between the EHT observations and the space-time zero-gravity radius provides the most conservative limit on the charge of Sgr A* to be |Q/M| < 2.32 in geometrized units. A charged naked singularity respecting this charge-to-mass constraint is consistent with the current EHT observations, if the image is not interpreted as a photon ring.

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Ruchi Mishra, Ronaldo S. S. Vieira, Włodek Kluźniak. 2023-04-09. Conservative limits on the electric charge of Sgr A* in the Reissner-Nordstrom metric. https://doi.org/10.1093/mnras/stae941

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