Light rings and long-lived modes in quasiblack hole spacetimes

Guo, Minyong; Zhong, Zhen; Wang, Jinguang; Gao, Sijie

doi:10.1103/physrevd.105.024049

Cited by 20 publications

(11 citation statements)

References 59 publications

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“…The relation between null geodesics and quasinormal modes has been rarely reported for black holes with more than one photon sphere. Moreover, multiple photon spheres appearing in some spacetime signal the existence of long-live modes, which may render the spacetime unstable [42][43][44]. Therefore, it is of great interest to study quasinormal modes of the hairy black holes endowed with three photon spheres.…”

Section: Jhep06(2022)060mentioning

confidence: 99%

“…Interestingly, a reflecting boundary in the wormhole or UCO spacetime can produce a set of time-delay echoes, which are characterized by quasinormal modes [38][39][40][41]. Furthermore, UCOs have been conjectured to suffer from instabilities due to the existence of a family of long-lived quasinormal modes, which appear in the neighborhood of a stable circular null geodesic [42][43][44]. For instance, a linear ergoregion instability associated with long-lived modes may occur for a spinning object with a sufficiently high rotation speed [45][46][47].…”

Section: Introductionmentioning

confidence: 99%

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Quasinormal modes of black holes with multiple photon spheres

Guo

Wang

Yang

et al. 2022

J. High Energ. Phys.

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For a static and spherically symmetric black hole, a photon sphere is composed of circular null geodesics of fixed radius, and plays an important role in observing the black hole. Recently, in an Einstein-Maxwell-scalar model with a non-minimal coupling between the scalar and electromagnetic fields, a class of hairy black holes has been found to possess two unstable and one stable circular null geodesics on the equatorial plane, corresponding to three photon spheres outside the event horizon. In this paper, we study quasinormal modes of the scalar field, which are associated with these circular null geodesics, in the hairy black hole spacetime. In the eikonal regime with l ≫ 1, the real part of the quasinormal modes is determined by the angular velocity of the corresponding circular geodesics. The imaginary part of the quasinormal modes associated with the unstable circular null geodesics encodes the information about the Lyapunov exponent of the corresponding circular geodesics. Interestingly, we find long-lived and sub-long-lived modes, which are associated with the stable and one of the unstable circular null geodesics, respectively. Due to tunneling through potential barriers, the damping times of the long-lived and sub-long-lived modes can be exponentially and logarithmically large in terms of l, respectively.

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Section: Jhep06(2022)060mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Quasinormal modes of black holes with multiple photon spheres

Guo

Wang

Yang

et al. 2022

J. High Energ. Phys.

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“…The results presented in [51] seem to indicate that light rings can only exist for unstable solutions. A recent work [52] also presents results that support that hypothesis. Another matter of astrophysical interest is whether such unstable solutions have a relatively short or a rather long life-time.…”

Section: Geodesic Motionmentioning

confidence: 59%

Extreme $\ell$-boson stars

Alcubierre,

Barranco,

Bernal

et al. 2021

Preprint

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A new class of complex scalar field objects, which generalize the well known boson stars, was recently found as solutions to the Einstein-Klein-Gordon system. The generalization consists in incorporating some of the effects of angular momentum, while still maintaining the spacetime's spherical symmetry. These new solutions depend on an (integer) angular parameter ℓ, and hence were named ℓ-boson stars. Like the standard ℓ = 0 boson stars these configurations admit a stable branch in the solution space; however, contrary to them they have a morphology that presents a shell-like structure with a "hole" in the internal region. In this article we perform a thorough exploration of the parameter space, concentrating particularly on the extreme cases with large values of ℓ. We show that the shells grow in size with the angular parameter, doing so linearly for large values, with the size growing faster than the thickness. Their mass also increases with ℓ, but in such a way that their compactness, while also growing monotonically, converges to a finite value corresponding to about one half of the Buchdahl limit. Furthermore, we show that ℓ-boson stars can be highly anisotropic, with the radial pressure diminishing relative to the tangential pressure for large ℓ, reducing asymptotically to zero, and with the maximum density also approaching zero. We show that these properties can be understood by analyzing the asymptotic limit ℓ → ∞ of the field equations and their solutions. We also analyze the existence and characteristics of both timelike and null circular orbits, especially for very compact solutions.

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“…Combining the parameter space for horizon and critical curves, one finds a particularly interesting region within the range 0.73576 l/M < 0.8 in which we have a kind of regular naked object with an accessible critical curve as well as an anti-photon sphere 2 , of this kind of models with such observations. 2 While the presence of anti-photon spheres can be able to trigger a non-perturbative instability [50][51][52][53][54], the time scales at which this may occur are model-dependent, thus not being a completely unsurmountable argument against the viability of solutions holding them.…”

Section: The Modelmentioning

confidence: 99%

Multi-ring images of thin accretion disk of a regular naked compact object

Guerrero,

Olmo,

Rubiera-Garcia

et al. 2022

Preprint

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We discuss the importance of multi-ring images in the optical appearance of a horizonless spherically symmetric compact object, when illuminated by an optically thin accretion disk. Such an object corresponds to a sub-case of an analytically tractable extension of the Kerr solution dubbed as the eye of the storm by Simpson and Visser in [JCAP 03 (2022) 011], which merits in removing curvature singularities via an asymptotically Minkowski core, while harbouring both a critical curve and an infinite potential barrier at the center for null geodesics. This multi-ring structure is induced by light rays winding several times around the object, and whose luminosity is significantly boosted as compared to the Schwarzschild solution by the modified shape of the potential. Using three toyprofiles for the emission of an infinitely thin disk, truncated at its inner edge (taking its maximum value there) and having different decays with the distance, we discuss the image created by up to eight rings superimposed on top of the direct emission of the disk as its edge is moved closer to the center of the object. Our results point out to the existence of multi-ring images with a non-negligible luminosity in shadow observations when one allows for the existence of other compact objects in the cosmic zoo beyond the Schwarzschild solution. Such multi-ring images could be detectable within the future projects on very-long baseline interferometry.

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Light rings and long-lived modes in quasiblack hole spacetimes

Cited by 20 publications

References 59 publications

Quasinormal modes of black holes with multiple photon spheres

Quasinormal modes of black holes with multiple photon spheres

Extreme $\ell$-boson stars

Multi-ring images of thin accretion disk of a regular naked compact object

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