Article
Astronomy & Astrophysics
Aydin Tavlayan, Bayram Tekin
Summary: The existence of light rings is closely related to black hole horizons and observables. We extend the arguments for unstable light rings in four-dimensional black holes to five-dimensional black holes, and show that there is a light ring for each rotation sense in a stationary black hole. Additionally, we find that when the black hole horizon disappears and the singularity becomes naked, only one of the light rings survives.
Article
Astronomy & Astrophysics
Rajes Ghosh, Sudipta Sarkar
Summary: The theorem presents a new understanding of light rings in stationary spacetimes with ergoregions. It proves that any stationary, axisymmetric, and asymptotically flat spacetime in 1 + 3 dimensions with an ergoregion must have at least one light ring outside the ergoregion. The possible extension of the proof for asymptotically de Sitter and anti-de Sitter spherically symmetric black holes is also addressed.
Article
Astronomy & Astrophysics
Gaston Giribet, Juan Laurnagaray, Pedro Schmied
Summary: In many cases, the near-horizon geometry can be used to compute conserved charges and thermodynamic quantities of gravitational solutions. These charges are Noether charges associated with asymptotic isometries that preserve appropriate boundary conditions at the future horizon. This paper demonstrates the application of such computations in higher-dimensional solutions with event horizons of nontrivial topology, using the 5-dimensional black ring as a particular focus.
Article
Astronomy & Astrophysics
Nuno M. Santos, Carlos A. R. Herdeiro
Summary: This paper explores how massless neutral scalar fields can form stationary clouds around a black hole, requiring conditions where spacetime is prone to superradiance and a confinement mechanism is present. It is found that only black holes with specific charge to mass ratios can support the existence of these stationary clouds.
Article
Astronomy & Astrophysics
Astrid Eichhorn, Aaron Held, Philipp-Vincent Johannsen
Summary: By observing the shadow images of black holes, we can investigate the effects of quantum gravity and other mechanisms on singularity resolution beyond traditional quantum gravity theories. Even the current accuracy of the Event Horizon Telescope (EHT) is sufficient to place meaningful constraints on the scale of new physics, when combined with an independent measurement of the black hole mass for M87*. Higher accuracy from the next-generation EHT is required for other spacetimes. Additionally, we study the concept of localized emission regions inspired by hotspots in accretion flows, as well as the photon-ring structure of horizonless objects where photon rings annihilate each other in the absence of photon spheres.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Physics, Particles & Fields
Alexandra Chanson, Victoria Martin, Maria J. Rodriguez, Luis Fernando Temoche
Summary: In this paper, we investigate the hidden conformal symmetry of black ring and black string solutions and show that it is not related to separability of the KG equation or the existence of a Killing-Yano tensor. Furthermore, we argue that these non-extremal black holes have a dual 2D CFT. We develop new revised monodromy techniques to cover all the cases considered.
JOURNAL OF HIGH ENERGY PHYSICS
(2023)
Article
Astronomy & Astrophysics
Pedro Bargueno
Summary: In this study, we use the Newman-Penrose formalism to establish results regarding the existence of external light rings in extremal black hole spacetimes. Under assumptions of flat or (anti)-de Sitter asymptotics, staticity, and the null energy condition, we show that a sufficient condition for the existence of external light rings is R < 2KG, where R is the curvature scalar of the spacetime and KG is the Gaussian curvature of a spacelike two-surface, both evaluated at the outermost event horizon that can have spherical, hyperbolic, or planar geometry. Our results apply to any metric gravity theory where photons follow null geodesics.
Article
Astronomy & Astrophysics
Wojciech Kulczycki, Patryk Mach, Edward Malec
Summary: In this study of stationary and axially symmetric black hole-disk systems, two branches of solutions are found to bifurcate based on specific entropy and rotation law parameter. Low entropy nuclear matter allows for the presence of moderately massive Keplerian disks.
Article
Astronomy & Astrophysics
Minyong Guo, Sijie Gao
Summary: The study reveals the existence of at least two light rings propagating in opposite directions around a nonextremal black hole, with the outermost one being radially unstable; and at least one retrograde light ring around an extremal black hole, with at least one being angularly stable.
Article
Astronomy & Astrophysics
Shahar Hod
Summary: This paper proves that spherically symmetric extremal black holes have at least one external light ring. Our remarkably compact proof is based on the dominant energy condition for the external matter fields in the nonvacuum asymptotically flat extremal black-hole spacetimes.
Article
Physics, Particles & Fields
Marco Astorino, Roberto Emparan, Adriano Vigano
Summary: This paper argues that expanding bubbles of nothing are a common feature in systems of black holes with multiple or non-spherical horizons. The authors provide explicit constructions in four and five dimensions to demonstrate this idea, showing that the geometries of expanding bubbles arise as a limit of static black hole binaries and black rings. They also discuss the possibility of similar constructions in higher dimensions, although numerical methods are often required. The paper concludes by suggesting that the Nariai solution can be understood as containing an expanding circular bubble of nothing.
JOURNAL OF HIGH ENERGY PHYSICS
(2022)
Article
Physics, Particles & Fields
M. Bianchi, D. Consoli, A. Grillo, J. F. Morales
Summary: This study focuses on massless geodesics near the photon-spheres of a large family of solutions of Einstein-Maxwell theory in five dimensions, revealing the presence of an unstable light ring of photon orbits surrounding the mass center. The Lyapunov exponent is computed to characterize the chaotic behavior of geodesics near the 'photon-sphere', showing that it is always bounded by its value for a Schwarzschild BH of the same mass in geometries free of naked singularities.
JOURNAL OF HIGH ENERGY PHYSICS
(2021)
Article
Astronomy & Astrophysics
F. G. Guzman, I Alvarez-Rios, J. A. Gonzalez
Summary: This paper presents a method to study the frequency shift of signals near a Schwarzschild black hole that grows or shrinks through accretion. By constructing numerical solutions of Einstein's equations sourced by spherical shells of scalar field with different energy densities, the study reveals the variability of photon frequency shift during the accretion process based on the thickness of the scalar field shell or the timescale of accretion, in relation to the dynamics of dust distribution.
Article
Astronomy & Astrophysics
Guo-Ping Li, Ke-Jian He
Summary: In this paper, the shadows and rings of the KS black hole in deformed HL gravity were carefully investigated using the ray-tracing method. The results show a decrease in certain parameters and an increase in effective potential with an increase in the omega parameter, with direct emissions dominating the total observed intensity.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Alejandro Ruiperez
Summary: We study the first-order alpha ' corrections to a general family of supersymmetric heterotic backgrounds that describe a rotating superposition of a fundamental string and a momentum wave. Even after taking into account these corrections, the singularity at the horizon of the resulting black ring in five dimensions persists, contrary to previous arguments in the literature.
CLASSICAL AND QUANTUM GRAVITY
(2021)
Article
Astronomy & Astrophysics
Nicolas Sanchis-Gual, Carlos Herdeiro, Eugen Radu
Summary: This study investigates the time evolution of spherical, excited boson star models and demonstrates that large self-interactions can stabilize the excited states. The formation of these states is found to occur through the gravitational cooling mechanism, starting from dilute initial data.
CLASSICAL AND QUANTUM GRAVITY
(2022)
Article
Astronomy & Astrophysics
C. Herdeiro, I. Perapechka, E. Radu, Ya. Shnir
Summary: Scalar boson stars and Dirac stars are solitonic solutions of the Einstein-Klein-Gordon and Einstein-Dirac classical equations, respectively. Despite the different bosonic vs. fermionic nature of the matter field, these solutions to the classical field equations have been shown to have qualitatively similar features. In particular, for spinning stars the most fundamental configurations can be in both cases toroidal, unlike spinning Proca stars that are spheroidal.
Article
Physics, Multidisciplinary
Pedro V. P. Cunha, Carlos Herdeiro, Eugen Radu, Nicolas Sanchis-Gual
Summary: Ultracompact objects with light rings but without an event horizon can mimic black holes in their strong gravity phenomenology. Through numerical simulations and the introduction of a novel technique, we confirm the instability triggered by the light rings and identify two possible outcomes: migration to nonultracompact configurations or collapse to black holes.
PHYSICAL REVIEW LETTERS
(2023)
Article
Astronomy & Astrophysics
Alejandro Cruz-Osorio, Lucian Rezzolla, Fabio D. Lora-Clavijo, Jose Antonio Font, Carlos Herdeiro, Eugen Radu
Summary: We present a numerical study of relativistic Bondi-Hoyle-Lyttleton accretion onto a black hole with synchronized hair. The steady-state solutions obtained provide insights into the formation of black holes in the presence of ultralight scalar fields and the possible association between the shock-cone and quasi-periodic oscillations in X-ray light curves.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Zeus S. Moreira, Haroldo C. D. Lima Jr, Luis C. B. Crispino, Carlos A. R. Herdeiro
Summary: In this study, we analyze the quasinormal modes (QNMs) of a Schwarzschild black hole with corrections motivated by Loop Quantum Gravity (LQG). The black hole exhibits a global structure of a black bounce, and the QNM frequency orbits in the complex plane are self-intersecting spiraling curves. The overall damping decreases with increasing LQG parameter, and the spectrum of the quantum corrected black hole shows an oscillatory pattern with possible QNMs having vanishing real part.
Article
Astronomy & Astrophysics
Marco Brito, Carlos Herdeiro, Eugen Radu, Nicolas Sanchis-Gual, Miguel Zilhao
Summary: We studied the time evolution of excited-scalar boson stars in general relativity coupled to a complex massive scalar field with quartic self-interactions. The stars with up to 10 radial nodes can be made dynamically stable for sufficiently large values of the self-interactions coupling constant lambda. The compactness of these solutions is insensitive to the number of radial nodes for large lambda and fixed frequency.
Article
Astronomy & Astrophysics
Carlos A. R. Herdeiro, Eugen Radu
Summary: We show that Einstein-scalar theories allow balanced static, neutral, asymptotically flat, double-black hole solutions with appropriate self-interactions. The solutions are scalar hairy versions of the double-Schwarzschild (or Bach-Weyl) solution, but regular on and outside the two horizons. The balancing repulsive force is provided by the scalar field.
Article
Astronomy & Astrophysics
Pedro Ildefonso, Miguel Zilhao, Carlos Herdeiro, Eugen Radu, Nuno M. Santos
Summary: In this study, dipolar self-interacting scalar boson stars are constructed and dynamically evolved in a model with sextic (or quartic) self-interactions. The domain of existence of dipolar Q-stars has a similar structure to that of fundamental monopolar stars in the same model. The evolutions show that the dipolar Q-stars exhibit similar dynamical properties: 1) in the Newtonian and relativistic branches, they are dynamically robust over longer time scales compared to dipolar stars without self-interactions; 2) in the middle branch, they migrate to either the Newtonian or the relativistic branch; 3) beyond the relativistic branch, they decay to black holes. Overall, these results strengthen the observation that self-interactions can mitigate dynamical instabilities of scalar boson star models.
Article
Astronomy & Astrophysics
Nuno M. Santos, Carlos A. R. Herdeiro, Eugen Radu
Summary: This study finds that in some models, scalarized BHs bifurcating from Reissner-Nordstrom and spinning BHs with synchronized hair bifurcating from Kerr do not have local thermodynamic stability.
Article
Astronomy & Astrophysics
P. Cunha, C. Herdeiro, E. Radu, Ya. Shnir
Summary: In this study, we construct and explore the equilibrium solution space of two nonspinning miniboson stars in fully nonlinear general relativity. We find that the equilibrium is reached through the balance between gravitational attraction and scalar mediated repulsion, enabled by a relative phase. We also propose a simple analytic model that qualitatively captures the variation of the proper distance between the stars with their mass.
Article
Astronomy & Astrophysics
Nicolas Sanchis-Gual, Juan Calderon Bustillo, Carlos Herdeiro, Eugen Radu, Jose A. Font, Samson H. W. Leong, Alejandro Torres-Forne
Summary: We present a systematic study of the dynamics and gravitational-wave emission of head-on collisions of spinning vector boson stars, known as Proca stars. We find that the wavelike nature of bosonic stars has a large impact on the gravitational-wave emission, leading to a nonmonotonic dependence of the emission on the frequency of the secondary star co2, for fixed frequency co1 of the primary. This may serve as a smoking gun to shed light on the possible existence of these objects.
Article
Astronomy & Astrophysics
Leong Khim Wong, Carlos A. R. Herdeiro, Eugen Radu
Summary: This study examines the constraining power of current gravitational-wave data on scalar-tensor-Gauss-Bonnet theories that allow for the spontaneous scalarization of black holes. The analysis includes two gravitational-wave events, and the results strongly disfavor specific values of lambda within the parameter space.
Article
Astronomy & Astrophysics
Victor Jaramillo, Nicolas Sanchis-Gual, Juan Barranco, Argelia Bernal, Juan Carlos Degollado, Carlos Herdeiro, Miguel Megevand, Dario Nunez
Summary: Fully nonlinear numerical evolutions of the Einstein-(multi)-Klein-Gordon equations are performed to study head-on collisions of t??-boson stars. The simulations indicate the formation of black holes, the formation of bound states of composite scalar fields, and deviations from spherical symmetry in the end products of the collisions.
Article
Astronomy & Astrophysics
Haroldo C. D. Lima Junior, Jian-Zhi Yang, Luis C. B. Crispino, Pedro V. P. Cunha, Carlos A. R. Herdeiro
Summary: The study investigates the characteristics of the generalized Schwarzschild-Melvin solution in Einstein-Maxwell-dilaton theory. It finds that the change in dilaton coupling a leads to a discontinuous transition of the topological charge (TC) from 0 to -1, which is related to the asymptotics and shadow effects of the Schwarzschild-Melvin solution.
Article
Astronomy & Astrophysics
Jorge F. M. Delgado, Carlos A. R. Herdeiro, Eugen Radu
Summary: This study focuses on the structure of timelike circular orbits (TCOs) near equatorial light rings (LRs) for stationary, axisymmetric, asymptotically flat, ultracompact objects with Z(2) north-south symmetry. The results show that the radial stability of LRs exclusively determines the structure of TCOs, suggesting potential applications for horizonless ultracompact objects and black holes.