Supermassive Black Holes or Boson Stars? Hair Counting With Gravitational Wave Detectors

Berti, Emanuele; Cardoso, Vítor

doi:10.1142/s0218271806009637

Cited by 53 publications

(53 citation statements)

References 29 publications

(43 reference statements)

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“…They computed the dominant axial oscillation modes and found no instabilities. In analogy with previous studies of the oscillation modes of boson stars [29][30][31], they confirmed that the axial QNM spectrum of gravastars can be used to discern a gravastar from a BH. In the thin-shell limit, the axial QNM frequencies of Ref.…”

Section: Introductionsupporting

confidence: 82%

“…Building on Ryan's proposal, Kesden et al showed that the inspiral of a small compact object into a nonrotating boson star will emit a rather different gravitational waveform at the end of the evolution, when the small object falls into the central potential well of the boson star instead of disappearing into the event horizon of a BH [28]. Several authors have computed the QNM spectrum of boson stars, showing that it is remarkably different from the QNM spectrum of BHs and lending support to the feasibility of no-hair tests using QNM measurements [29][30][31].…”

Section: Introductionmentioning

confidence: 99%

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Gravitational wave signatures of the absence of an event horizon: Nonradial oscillations of a thin-shell gravastar

et al. 2009

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Gravitational waves from compact objects provide information about their structure, probing deep into strong-gravity regions. Here we illustrate how the presence or absence of an event horizon can produce qualitative differences in the gravitational waves emitted by ultracompact objects. In order to set up a straw-man ultracompact object with no event horizon, but which is otherwise almost identical to a black hole, we consider a nonrotating thin-shell model inspired by Mazur and Mottola's gravastar, which has a Schwarzschild exterior, a de Sitter interior and an infinitely thin shell with finite tension separating the two regions. As viewed from the external space-time, the shell can be located arbitrarily close to the Schwarzschild radius, so a gravastar might seem indistinguishable from a black hole when tests are only performed on its external metric. We study the linearized dynamics of the system, and, in particular, the junction conditions connecting internal and external gravitational perturbations. As a first application of the formalism we compute polar and axial oscillation modes of a thin-shell gravastar. We show that the quasinormal mode spectrum is completely different from that of a black hole, even in the limit when the surface redshift becomes infinite. Polar quasinormal modes depend on the equation of state of matter on the shell and can be used to distinguish between different gravastar models. Our calculations suggest that low-compactness gravastars could be unstable when the sound speed on the shell v s =c * 0:92.

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Section: Introductionsupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Gravitational wave signatures of the absence of an event horizon: Nonradial oscillations of a thin-shell gravastar

et al. 2009

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“…Therefore a measurement of the frequency and damping time of a QNM can be used to infer the mass and angular momentum of the BH with potentially high accuracy [9,79,10,11]. Since the whole QNM spectrum depends solely on M and a, the measurement of two or more QNM frequencies provides a stringent observational test of the no-hair theorem of general relativity [461,462,11,463]. The prospects for detecting the signature of BH oscillations in gravitational waves are the main topic of this section.…”

Section: Quasinormal Modes Of Astrophysical Black Holesmentioning

confidence: 99%

“…In conclusion, ringdown radiation can be used to distinguish BHs from exotic alternatives, such as boson stars [463] or gravastars [664]. Ringdown tests of the Kerr nature of astrophysical BHs are independent from (and complementary to) proposed tests using a multipolar mapping of the Kerr spacetime, as encoded in EMRI signals according to "Ryan's theorem" and its generalizations [665,666,667].…”

Section: Tests Of the No-hair Theoremmentioning

confidence: 99%

Quasinormal modes of black holes and black branes

Berti

Cardoso

Starinets

2009

Class. Quantum Grav.

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1,826

2,169

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Abstract. Quasinormal modes are eigenmodes of dissipative systems. Perturbations of classical gravitational backgrounds involving black holes or branes naturally lead to quasinormal modes. The analysis and classification of the quasinormal spectra requires solving non-Hermitian eigenvalue problems for the associated linear differential equations. Within the recently developed gauge-gravity duality, these modes serve as an important tool for determining the near-equilibrium properties of strongly coupled quantum field theories, in particular their transport coefficients, such as viscosity, conductivity and diffusion constants. In astrophysics, the detection of quasinormal modes in gravitational wave experiments would allow precise measurements of the mass and spin of black holes as well as new tests of general relativity. This review is meant as an introduction to the subject, with a focus on the recent developments in the field.

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“…We remark that boson stars have been suggested as BH mimickers, and studies in this context, including of the comparative phenomenology, have been report in, e.g. [53][54][55][56][57][58][59][60][61][62][63][64].…”

Section: Introductionmentioning

confidence: 99%

Iron Kα line of boson stars

Cao

Cárdenas-Avendaño

Zhou

et al. 2016

J. Cosmol. Astropart. Phys.

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Abstract. The present paper is a sequel to our previous work [Y. Ni et al., JCAP 1607, 049 (2016] in which we studied the iron Kα line expected in the reflection spectrum of Kerr black holes with scalar hair. These metrics are solutions of Einstein's gravity minimally coupled to a massive, complex scalar field. They form a continuous bridge between a subset of Kerr black holes and a family of rotating boson stars depending on one extra parameter, the dimensionless scalar hair parameter q, ranging from 0 (Kerr black holes) to 1 (boson stars). Here we study the limiting case q = 1, corresponding to rotating boson stars. For comparison, spherical boson stars are also considered. We simulate observations with XIS/Suzaku. Using the fact that current observations are well fit by the Kerr solution and thus requiring that acceptable alternative compact objects must be compatible with a Kerr fit, we find that some boson star solutions are relatively easy to rule out as potential candidates to explain astrophysical black holes, while other solutions, which are neither too dilute nor too compact are more elusive and we argue that they cannot be distinguished from Kerr black holes by the analysis of the iron line with current X-ray facilities.

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Supermassive Black Holes or Boson Stars? Hair Counting With Gravitational Wave Detectors

Cited by 53 publications

References 29 publications

Gravitational wave signatures of the absence of an event horizon: Nonradial oscillations of a thin-shell gravastar

Gravitational wave signatures of the absence of an event horizon: Nonradial oscillations of a thin-shell gravastar

Quasinormal modes of black holes and black branes

Iron Kα line of boson stars

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