Non-equatorial scalar rings supported by rapidly spinning Gauss-Bonnet black holes

TL;DR

This paper demonstrates the existence of non-equatorial scalar rings supported by rapidly spinning Gauss-Bonnet black holes, revealing new stable matter configurations in modified gravity theories.

Contribution

It proves the existence of non-equatorial scalar rings around Kerr black holes in the large-spin regime within Einstein-Gauss-Bonnet theory, a novel configuration not previously known.

Findings

Rapidly rotating Kerr black holes can support non-equatorial scalar rings.

Non-equatorial scalar rings are characterized by a specific functional relation in the large-mass limit.

The study extends understanding of matter configurations in modified gravity theories.

Abstract

Black-hole spacetimes that possess stationary equatorial matter rings are known to exist in general relativity. We here reveal the existence of black-hole spacetimes that support {\it non}-equatorial matter rings. In particular, it is proved that rapidly-rotating Kerr black holes in the dimensionless large-spin regime ${\bar a}>{\bar a}_{\text{crit}}= \sqrt{\big\{{{7+\sqrt{7}\cos\big[{1\over3}\arctan\big(3\sqrt{3}\big)\big]- \sqrt{21}\sin\big[{1\over3}\arctan\big(3\sqrt{3}\big)\big]}\big\}/12}}\simeq0.78$ can support a pair of non-equatorial massive scalar rings which are negatively coupled to the Gauss-Bonnet curvature invariant of the spinning spacetime (here ${\bar a}\equiv J/M^2$ is the dimensionless angular momentum of the central supporting black hole). We explicitly prove that these non-equatorial scalar rings are characterized by the dimensionless functional relation $-{{57+28\sqrt{21}\cos\big[{1\over3}\arctan\big({{1}\over{3\sqrt{3}}}\big)\big]} \over{8(1+\sqrt{1-{\bar a}^2})^6}} \cdot{{\bar\eta}\over{{\bar\mu}^2}}\to 1^{+}$ in the large-mass ${\bar\mu}\equiv M\mu\gg1$ regime (here $\{{\bar\eta}<0,\mu\}$ are respectively the non-trivial coupling parameter of the composed Einstein-Gauss-Bonnet-massive-scalar field theory and the proper mass of the supported non-minimally coupled scalar field).