Penrose process in magnetized non-Kerr rotating spacetime with anomalous quadrupole moment

TL;DR

This paper explores how magnetic fields and anomalous quadrupole moments in a non-Kerr spacetime affect the magnetic Penrose process, revealing conditions for enhanced energy extraction and potential astrophysical applications.

Contribution

It introduces the impact of quadrupole moments and magnetic fields on the magnetic Penrose process in a non-Kerr spacetime, highlighting new efficiency behaviors and operational regions.

Findings

Efficiency can exceed that of the mechanical Penrose process.

Negative quadrupole moments optimize efficiency without magnetic fields.

Aligned charge and magnetic field enhance efficiency in electromagnetic dominance.

Abstract

We investigate the magnetic Penrose process in the Quevedo-Mashhoon spacetime, immersed in a uniform magnetic field $B$. This metric is a stationary, axisymmetric, asymptotically flat vacuum solution to Einstein's equations with an arbitrary anomalous quadrupole moment ${\cal Q}$. A non-vanishing ${\cal Q}$ significantly modifies the near-horizon geometry, creating a multi-lobe ergoregion. Both ${\cal Q}$ and $B$ strongly influence the negative-energy region, which can extend well beyond the ergoregion, enabling the magnetic Penrose process to operate far from the ergoregion. Their combined effects allow energy extraction efficiency $\eta$ to far exceed that of the mechanical Penrose process. The maximum efficiency undergoes three distinct evolutionary stages as ${\cal Q}$ varies. In the absence of the magnetic field, efficiency is optimized for more negative ${\cal Q}$ (yielding a more oblate spacetime than Kerr). When electromagnetic interactions dominate, efficiency peaks when the infalling fragment's charge and $B$ share the same sign and ${\cal Q}$ is more positive (producing a more prolate spacetime than Kerr). These findings support the magnetic Penrose process as a theoretical framework for high-energy cosmic phenomena (e.g., extragalactic high-energy radiation) and as a tool to test the Kerr hypothesis.