Quasinormal Modes of Black Holes with Multiple Photon Spheres

Guo, Guangzhou; Wang, Peng; Wu, Houwen; Yang, Haitang

doi:10.48550/arxiv.2112.14133

Cited by 9 publications

(24 citation statements)

References 60 publications

(93 reference statements)

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“…Furthermore, the QNM frequency can also partly reveal the stability of spacetime geometry under small perturbations [86,87]. Hence, the study of QNM has become a concerned topic [88][89][90][91].…”

Section: Introductionmentioning

confidence: 99%

Quasinormal modes of black holes in f(T) gravity

Zhao¹,

Ren²,

Ilyas³

et al. 2022

Preprint

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We calculate the quasinormal modes (QNM) frequencies of a test massless scalar field around static black holes in f (T ) gravity. Focusing on quadratic f (T ) modifications, which is a good approximation for every realistic f (T ) theory, we first extract the spherically symmetric solutions using the perturbative method, imposing two ansätze for the metric functions, which suitably quantify the deviation from the Schwarzschild solution. Moreover, we extract the effective potential and then we calculate the QNM frequency of the obtained solutions. Firstly, we solve the Schrödinger-like equation numerically using the discretization method, and we extract the frequency and the time evolution of the dominant mode applying the function fit method. Secondly, we perform a semianalytical calculation by applying the third-order WKB approximation method. We show that the results for f (T ) gravity are different comparing to General Relativity, and in particular we obtain a different slope and period of the field decay behavior for different values of the model parameter. Hence, under the light of gravitational-wave observations of increasing accuracy from binary systems, the whole analysis could be used as an additional tool in order to test General Relativity and examine whether torsional gravitational modifications are possible.

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Section: Introductionmentioning

confidence: 99%

Quasinormal modes of black holes in f(T) gravity

Zhao¹,

Ren²,

Ilyas³

et al. 2022

Preprint

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“…In recent works [78,79], we found that the hairy black holes can also possess multiple photon spheres outside the event horizon, which have significant effects on the optical observation of black holes illuminated by the surrounding accretion disk, e.g., leading to bright rings of different radii in the black hole images [78] and significantly increasing the flux of the observed images [79]. Later, it showed that the effective potential for a scalar perturbation in the hairy black holes exhibits a double-peak structure [80]. In the eikonal limit, the extrema of the double-peak potential correspond to the photon spheres, around which long-lived and sub-long-lived quasinormal modes were found [80].…”

mentioning

confidence: 75%

“…Later, it showed that the effective potential for a scalar perturbation in the hairy black holes exhibits a double-peak structure [80]. In the eikonal limit, the extrema of the double-peak potential correspond to the photon spheres, around which long-lived and sub-long-lived quasinormal modes were found [80]. The appearance of the double-peak effective potentials naturally motivates us to search echo signals of perturbations in the hairy black holes.…”

mentioning

confidence: 99%

“…The appearance of the double-peak effective potentials naturally motivates us to search echo signals of perturbations in the hairy black holes. Moreover, it is highly desirable to explore the relationship between echoes and the long-lived and sub-long-lived modes obtained in [80]. To this end, we numerically obtain time-domain echoes of scalar perturbations in the hairy black holes and reconstruct the late-time signals from associated quasinormal modes in this paper.…”

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confidence: 99%

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Echoes from Hairy Black Holes

Guo,

Wang,

et al. 2022

Preprint

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We study the waveforms of time signals produced by scalar perturbations in static hairy black holes, in which the perturbations can be governed by a double-peak effective potential.The inner potential peak would give rise to echoes, which provide a powerful tool to test the Kerr hypothesis. The waveforms are constructed in the time and frequency domains, and we find that the late-time waveforms are determined by the long-lived and sub-long-lived quasinormal modes, which are trapped in the potential valley and near the smaller peak, respectively. When the distance between the peaks is significantly larger than the width of the peaks, a train of decaying echo pulses is produced by the superposition of the long-lived and sub-long-lived modes. In certain cases, the echoes can vanish and then reappear. When the peaks are close enough, one detects far fewer echo signals and a following sinusoid tail, which is controlled by the long-lived or sub-long-lived mode and hence decays very slowly.

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“…The existence of two photon spheres can significantly affect the optical appearance of HBHs illuminated by the surrounding accretion disk, e.g., producing bright rings of different radus in the black hole images [88] and noticeably increasing the flux of the observed images [89]. Moreover, the effective potential for a scalar perturbation in the HBHs with two photon spheres was shown to exhibit a double-peak structure, leading to long-lived quasinormal modes [90] and echo signals [91]. It is worth noting that the existence of two photon spheres outside the event horizon has also been reported for dyonic black holes with a quasi-topological electromagnetic term [92] and black holes in massive gravity [93,94].…”

Section: Numerical Resultsmentioning

confidence: 99%

Gravitational Lensing by Black Holes with Multiple Photon Spheres

Guo,

Jiang,

Wang

et al. 2022

Preprint

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We study gravitational lensing of light by hairy black holes, which, in a certain parameter regime, can possess two photon spheres of different size outside the event horizon. In particular, we focus on higher-order images of a point-like light source and a luminous celestial sphere produced by strong gravitational lensing near photon spheres. Two photon spheres usually triple the number of high-order images of a point-like light source. When a hairy black hole is illuminated by a celestial sphere, two photon spheres would give rise to two critical curves in the black hole image, and the smaller critical curve coincides with the shadow edge. In addition to a set of higher-order images of the celestial sphere outside the shadow edge, two more sets of higher-order images are observed inside and outside the larger critical curve, respectively.

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Quasinormal Modes of Black Holes with Multiple Photon Spheres

Cited by 9 publications

References 60 publications

Quasinormal modes of black holes in f(T) gravity

Quasinormal modes of black holes in f(T) gravity

Echoes from Hairy Black Holes

Gravitational Lensing by Black Holes with Multiple Photon Spheres

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