Extreme Spacetime Research Articles

Motion of particles around a magnetically charged Euler–Heisenberg black hole with scalar hair and the Event Horizon Telescope

We study the motion of uncharged particles and photons in the background of a magnetically charged Euler–Heisenberg (EH) black hole (BH) with scalar hair. The spacetime can be asymptotically (A)dS or flat. After investigating particle motions around the BH and the behavior of the effective potential of the particle radial motion, we determine the contribution of the BH parameters to the geodesics. Photons follow null geodesics of an effective geometry induced by the corrections of the EH non-linear electrodynamics. Thus, after determining the effective geometry, we calculate the shadow of the BH. We also analyze in detail the case of extremal BH spacetimes and we find that the radius of both the event horizon and shadow exhibits discontinuities when varying with respect to either the magnetic charge or the scalar charge. These extremal scenarios exist for sufficiently small values of the EH parameter, and imply the formation of a second photon ring around the BH shadow. Upon comparing the theoretically calculated BH shadow to the images of the shadows of M87* and Sgr A* observed by the Event Horizon Telescope collaboration, we impose constraints on the BH parameters, namely the scalar hair (ν\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ u $$\\end{document}), the magnetic charge (Qm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Q_{m}$$\\end{document}) and the EH parameter (α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha $$\\end{document}). For sufficiently large values of the EH parameter, our model is in agreement with the EHT observations for approximately every value for the BH magnetic charge.

A regular version of the extremal RN spacetime

A modified extremal Reissner-Nordstrom geometry, void of singularities, is proposed in this work, by means of an exponential factor depending on a positive constant k. All the metric coefficients are positive and finite and the spacetime has no any horizon. The curvature invariants are regular at the origin of coordinates and at infinity. The energy conditions for the stress tensor associate to the imperfect fluid are investigated. The gravitational field presents repulsive properties near the gravitational radius associated to the mass m. With the choice k=1/m, the Komar energy WK of the mass m changes its sign at r=λ (λ is the Compton wavelength of m), when the classical energy mc2 equals the energy ħc/r.

Extremal black holes have external light rings

It is proved that spherically symmetric extermal black holes possess at least one external light ring. Our remarkably compact proof is based on the dominant energy condition which characterizes the external matter fields in the non-vacuum extremal black-hole spacetimes.

Do the Einstein-matter field equations always predict the existence of light rings in black-hole spacetimes?

We are used to think of null circular geodesics as an integral part of black-hole spacetimes. In the present compact paper we reveal the physically interesting fact that, contrary to the general belief, the non-linearly coupled Einstein-matter field equations do not a priori guarantee the existence of external light rings in extremal black-hole spacetimes. This observation raises the intriguing possibility of having extremal black-hole spacetimes that possess no external light rings. We prove that these unique black holes, if exist, are characterized by non-positive tangential pressures on their surfaces.

Simulating superluminal propagation of Dirac particles using trapped ions

Simulating quantum phenomena in extreme spacetimes in the laboratory represents a powerful approach to explore fundamental physics in the interplay of quantum field theory and general relativity. Here we propose to simulate the movement of a Dirac particle propagating with a superluminal velocity caused by the emergent Alcubierre warp drive spacetime using trapped ions. We demonstrate that the platform allows observing the tilted lightcone that manifests as a superluminal velocity, which is in agreement with the prediction of general relativity. Furthermore, the Zitterbewegung effect arising from relativistic quantum mechanics persists with the superluminal propagation and is experimentally measurable. The present scheme can be extended to simulate the Dirac equation in other exotic curved spacetimes, thus provides a versatile tool to gain insights into the fundamental limit of these extreme spacetimes.

Waveforms and fluxes: Towards a self-consistent effective one body waveform model for nonprecessing, coalescing black-hole binaries for third generation detectors

We present a comprehensive comparison between numerical relativity (NR) angular momentum fluxes at infinity and the corresponding quantity entering the radiation reaction in TEOBResumS, an Effective-One-Body (EOB) waveform model for nonprecessing coalescing black hole binaries on quasi-circular orbits. This comparison prompted us to implement two changes in the model: (i) including Next-to-Quasi-Circular corrections in the $\ell=m$, $\ell\leq 5$ multipoles entering the radiation reaction and (ii) consequently updating the NR-informed spin-orbital sector of the model. This yields a new waveform model that presents a higher self-consistency between waveform and dynamics and an improved agreement with NR simulations. We test the model computing the EOB/NR unfaithfulness $\bar{F}_{\rm EOB/NR}$ over all 534 spin-aligned configurations available through the Simulating eXtreme Spacetime catalog, notably using the noise spectral density of Advanced LIGO, Einstein Telescope and Cosmic Explorer, for total mass up to $500M_\odot$. We find that the maximum unfaithfulness $\bar{F}^{\rm max}_{\rm EOB/NR}$ is mostly between $10^{-4}$ and $10^{-3}$, and the performance progressively worsens up to $\sim 5\times 10^{-3}$ as the effective spin of the system is increased. We perform similar analyses on the \SEOB{} model, that delivers $\bar{F}^{\rm max}_{\rm EOB/NR}$ values uniformly distributed versus effective spin and mostly between $10^{-3}$ and $10^{-2}$. We conclude that the improved TEOBResumS model already represents a reliable and robust first step towards the development of highly accurate waveform templates for third generation detectors.

Response of an Unruh-DeWitt detector near an extremal black hole

We consider the response of an Unruh-DeWitt detector near an extremal charged black hole, modeling the near-horizon region of this extremal spacetime by the Bertotti-Robinson spacetime. The advantage of employing the Bertotti-Robinson limit is that the two-point functions for a massless scalar field are obtainable in closed form for the field in a number of quantum states of interest. We consider the detector coupled to a massless field in both the Boulware vacuum state and arbitrary thermal states, including the Hartle-Hawking state, and analyse the detector's response for a broad range of trajectories. Particular attention is paid to the thermalization of the detector, the anti-Unruh and anti-Hawking effect.

Effective-one-body multipolar waveforms for eccentric binary black holes with nonprecessing spins

We construct an inspiral-merger-ringdown eccentric gravitational-wave (GW) model for binary black holes with non-precessing spins within the effective-one-body formalism. This waveform model, SEOBNRv4EHM, extends the accurate quasi-circular SEOBNRv4HM model to eccentric binaries by including recently computed eccentric corrections up to 2PN order in the gravitational waveform modes, notably the $(l,|m|)=(2,2),(2,1),(3,3),(4,4),(5,5)$ multipoles. The waveform model reproduces the zero eccentricity limit with an accuracy comparable to the underlying quasi-circular model, with the unfaithfulness of $\lesssim1\%$ against quasi-circular numerical-relativity (NR) simulations. When compared against 28 public eccentric NR simulations from the Simulating eXtreme Spacetimes catalog with initial orbital eccentricities up to $e\simeq0.3$ and dimensionless spin magnitudes up to $+0.7$, the model provides unfaithfulness $<1\%$, showing that both the $(2,|2|)$-modes and the higher-order modes are reliably described without calibration to NR datasets in the eccentric sector. The waveform model SEOBNRv4EHM is able to qualitatively reproduce the phenomenology of dynamical captures, and can be extended to include spin-precession effects. It can be employed for upcoming observing runs with the LIGO-Virgo-KAGRA detectors and used to re-analyze existing GW catalogs to infer the eccentricity parameters for binaries with $e\lesssim0.3$ (at 20 Hz or lower) and spins up to $\lesssim 0.9-0.95$. The latter is a promising region of the parameter space where some astrophysical formation scenarios of binaries predict mild eccentricity in the ground-based detectors' bandwidth. Assessing the accuracy and robustness of the eccentric waveform model SEOBNRv4EHM for larger eccentricities and spins will require comparisons with, and, likely, calibration to eccentric NR waveforms in a larger region of the parameter space.

A higher-multipole gravitational waveform model for an eccentric binary black holes based on the effective-one-body-numerical-relativity formalism

We have previously constructed a waveform model, , for spinning binary black hole (BBH) moving along eccentric orbit based on effective-one-body (EOB) formalism. In the current paper, we update waveform model in the following three respects. Firstly, we update the EOB dynamics from to . Secondly we properly treat the Schott term which has been ignored in previous . Thirdly, we construct a new factorized waveform including (l, |m|) = (2, 2), (2, 1), (3, 3), (4, 4) modes based on EOB formalism, which is valid for spinning BBHs in general equatorial orbit. Following our previous waveform model, we call our new waveform model . The (l, |m|) = (2, 2) mode waveform of can fit the original waveform very well in the case of a quasi-circular orbit. We have validated waveform model through comparing the waveform against the Simulating eXtreme Spacetimes (SXS) catalog. The comparison is done for BBH with total mass in (20, 200)M ⊙ using Advanced LIGO designed sensitivity. For the quasi-circular cases we have compared our (2, 2) mode waveforms to the 281 numerical relativity (NR) simulations of BBH along quasi-circular orbits. All of the matching factors are bigger than 98%. For the elliptical cases, 24 NR simulations of BBH along an elliptic orbit are used. For each elliptical BBH system, we compare our modeled gravitational polarizations against the NR results for different combinations of the inclination angle, the initial orbit phase and the source localization in the sky. We use the minimal matching factor respect to the inclination angle, the initial orbit phase and the source localization to quantify the performance of the higher modes waveform. We found that after introducing the higher modes, the minimum of the minimal matching factor among the 24 tested elliptical BBHs increases from 90% to 98%. Our waveform model can match all tested 305 SXS waveforms better than 98% including highly spinning (χ = 0.99) BBH, highly eccentric (e ≈ 0.6 at reference frequency Mf 0 = 0.002) BBH and large mass ratio (q = 10) BBH.

Gravitation in Theory of Space-Time Film and Galactic Soliton

The scalar field of extremal space-time film is considered as unified fundamental field. Metrical interaction between solitons-particles as gravitational interaction is considered here in approximation of a weak fundamental field. It is shown that the signature of metrics {-,+,+,+} in the model formulation provides the observable gravitational attraction to a region with bigger energy density of the fundamental field. The induced gravitational interaction in the space-time film theory is applied to stars in a galaxy. The conception of galaxy soliton of space-time film is introduced. A weak field asymptotic solution for a galaxy soliton is proposed. It is shown that the effective metrics for this solution can provide the observable velocity curves for galaxies and explains their spiral structure. Thus a solution for so-called dark matter problem in the framework of space-time film theory is proposed.

Pseudospectrum of Reissner-Nordström black holes: Quasinormal mode instability and universality

Black hole spectroscopy is a powerful tool to probe the Kerr nature of astrophysical compact objects and their environment. The observation of multiple ringdown modes in gravitational waveforms could soon lead to high-precision gravitational spectroscopy, so it is critical to understand if the quasinormal mode spectrum is stable against perturbations. It was recently shown that the pseudospectrum can shed light on the spectral stability of black hole quasinormal modes. We study the pseudospectrum of Reissner-Nordstr\"om spacetimes and we find a spectral instability of scalar and gravitoelectric quasinormal modes in subextremal and extremal black holes, extending similar findings for the Schwarzschild spacetime. The asymptotic structure of pseudospectral contour levels is the same for scalar and gravitoelectric perturbations. By making different gauge choices in the hyperboloidal slicing of the spacetime, we find that the broad features of the pseudospectra are remarkably gauge-independent. The gravitational-led and electromagnetic-led quasinormal modes of extremal Reissner-Nordstr\"om black holes exhibit "strong" isospectrality: not only their spectrum coincides, but the whole pseudospectrum is the same for both classes of perturbations. We observe that a conformal duality between the extremal horizon and spacetime boundaries at infinity is responsible for such "strong" isospectrality property.

Comparing remnant properties from horizon data and asymptotic data in numerical relativity

We present a new study of remnant black hole properties from 13 binary black hole systems, numerically evolved using the Spectral Einstein Code. The mass, spin, and recoil velocity of each remnant were determined quasi-locally from apparent horizon data and asymptotically from Bondi data $(h, \psi_4, \psi_3, \psi_2, \psi_1)$ computed at future null infinity using SpECTRE's Cauchy characteristic evolution. We compare these independent measurements of the remnant properties in the bulk and on the boundary of the spacetime, giving insight into how well asymptotic data are able to reproduce local properties of the remnant black hole in numerical relativity. We also discuss the theoretical framework for connecting horizon quantities to asymptotic quantities and how it relates to our results. This study recommends a simple improvement to the recoil velocities reported in the Simulating eXtreme Spacetimes waveform catalog, provides an improvement to future surrogate remnant models, and offers new analysis techniques for evaluating the physical accuracy of numerical simulations.

Effective one-body multipolar waveform model for spin-aligned, quasicircular, eccentric, hyperbolic black hole binaries

Building upon recent work, we present an improved effective-one-body (EOB) model for spin-aligned, coalescing, black hole binaries with generic orbital configurations, i.e. quasi-circular, eccentric or hyperbolic orbits. The model relies on the idea of incorporating general Newtonian prefactors, instead of the usual quasi-circular ones, in both radiation reaction and waveform. The major advance with respect to previous work is that the quasi-circular limit of the model is now correctly informed by numerical relativity (NR) quasi-circular simulation. This provides EOB/NR unfaithfulness for the dominant quadrupolar waveform, calculated with Advanced LIGO noise, at most of the order of $1\%$ over a meaningful portion of the quasi-circular NR simulations calculated by the Simulating eXtreme Spacetime (SXS) collaboration. In the presence of eccentricity, the model is similarly NR-faithful, $\lesssim 1\%$, all over the 28 public SXS NR datasets, with initial eccentricity up to $\simeq 0.2$ , mass ratio up to $q=3$ and dimensionless spin magnitudes as large as $+0.7$. Higher multipoles, up to $\ell=5$ are also reliably modeled through the eccentric inspiral, plunge merger and ringdown. For hyperbolic-like configurations, we also show that the EOB computed scattering angle is in excellent agreement with all currently available NR results.

Stationary Solutions to the Stochastic Burgers Equation on the Line

We consider invariant measures for the stochastic Burgers equation on \({\mathbb {R}}\), forced by the derivative of a spacetime-homogeneous Gaussian noise that is white in time and smooth in space. An invariant measure is indecomposable, or extremal, if it cannot be represented as a convex combination of other invariant measures. We show that for each \(a\in {\mathbb {R}}\), there is a unique indecomposable law of a spacetime-stationary solution with mean a, in a suitable function space. We also show that solutions starting from spatially-decaying perturbations of mean-a periodic functions converge in law to the extremal space-time stationary solution with mean a as time goes to infinity.

Extending gravitational wave extraction using Weyl characteristic fields

We present a detailed methodology for extracting the full set of Newman-Penrose Weyl scalars from numerically generated spacetimes without requiring a tetrad that is completely orthonormal or perfectly aligned to the principal null directions. We also describe how to implement an extrapolation technique for computing the Weyl scalars' contribution at asymptotic null infinity in postprocessing. These methods have been used to produce $\Psi_4$ and $h$ waveforms for the Simulating eXtreme Spacetimes (SXS) waveform catalog and now have been expanded to produce the entire set of Weyl scalars. These new waveform quantities are critical for the future of gravitational wave astronomy in order to understand the finite-amplitude gauge differences that can occur in numerical waveforms. We also present a new analysis of the accuracy of waveforms produced by the Spectral Einstein Code. While ultimately we expect Cauchy characteristic extraction to yield more accurate waveforms, the extraction techniques described here are far easier to implement and have already proven to be a viable way to produce production-level waveforms that can meet the demands of current gravitational-wave detectors.

Adding gravitational memory to waveform catalogs using BMS balance laws

Accurate models of gravitational waves from merging binary black holes are crucial for detectors to measure events and extract new science. One important feature that is currently missing from the Simulating eXtreme Spacetimes (SXS) Collaboration's catalog of waveforms for merging black holes, and other waveform catalogs, is the gravitational memory effect: a persistent, physical change to spacetime that is induced by the passage of transient radiation. We find, however, that by exploiting the Bondi-Metzner-Sachs (BMS) balance laws, which come from the extended BMS transformations, we can correct the strain waveforms in the SXS catalog to include the missing displacement memory. Our results show that these corrected waveforms satisfy the BMS balance laws to a much higher degree of accuracy. Furthermore, we find that these corrected strain waveforms coincide especially well with the waveforms obtained from Cauchy-characteristic extraction (CCE) that already exhibit memory effects. These corrected strain waveforms also evade the transient junk effects that are currently present in CCE waveforms. Lastly, we make our code for computing these contributions to the BMS balance laws and memory publicly available as a part of the python package $\texttt{sxs}$, thus enabling anyone to evaluate the expected memory effects and violation of the BMS balance laws.

Rotating dyonic black hole in , U(1)2 gauged supergravity as natural laboratory for high energy particle collisions

In the present work, we explore several gravitational aspects such as energy extraction (via the Penrose process and superradiance), particle collisions around a , U(1)2 rotating dyonic black hole (BH) in the gauged supergravity model. The influence of the rotation parameter (a) and the gauge coupling constant (g) on the behavior of the horizon and ergoregion of the BH is investigated. In comparison to the extremal Kerr BH, the gauge coupling constant, under certain constraints, can interestingly enhance the maximum efficiency of energy extraction through the Penrose process by almost twice. Under the same constraints, we can extract approximately 60.75% of the initial mass-energy from the BH which is noticeably higher and far different from that of the Kerr BH. The limit of energy extraction in terms of the local speeds of the fragments is also determined with the help of the Wald inequality. We discover an upper limit on the gauge coupling constant up to which superradiance is likely to occur. Finally, we estimate the center-of-mass energy (E CM) of two particles with the same rest mass moving in the equatorial plane of the BH. Our study also aims to sensitize E CM to the parameters a and g for both extremal and nonextremal spacetime. Especially, for the extremal case, an infinitely large amount of E CM can be achieved closer to the event horizon confirming a basic point of view that an extreme supergravity BH with dyons could serve as ultimate particle accelerators as compared to Kerr and any other generalized BHs in this family and other alternative theories of gravity. However, E CM for the nonextremal spacetime is shown to be finite and has an upper bound.

Generalized Pareto processes for simulating space-time extreme events: an application to precipitation reanalyses

To better manage the risks of destructive natural disasters, impact models can be fed with simulations of extreme scenarios to study the sensitivity to temporal and spatial variability. We propose a semi-parametric stochastic framework that enables simulations of realistic spatio-temporal extreme fields using a moderate number of observed extreme space-time episodes to generate an unlimited number of extreme scenarios of any magnitude. Our framework draws sound theoretical justification from extreme value theory, building on generalized Pareto limit processes arising as limits for event magnitudes exceeding a high threshold. Specifically, we exploit asymptotic stability properties by decomposing extreme event episodes into a scalar magnitude variable (that is resampled), and an empirical profile process representing space-time variability. For illustration on hourly gridded precipitation data in Mediterranean France, we calculate various risk measures using extreme event simulations for yet unobserved magnitudes, and we highlight contrasted behavior for different definitions of the magnitude variable.

Multipolar effective-one-body waveforms for precessing binary black holes: Construction and validation

As gravitational-wave detectors become more sensitive, we will access a greater variety of signals emitted by compact binary systems, shedding light on their astrophysical origin and environment. A key physical effect that can distinguish among formation scenarios is the misalignment of the spins with the orbital angular momentum, causing the spins and the binary's orbital plane to precess. To accurately model such systems, it is crucial to include multipoles beyond the dominant quadrupole. Here, we develop the first multipolar precessing waveform model in the effective-one-body (EOB) formalism for the inspiral, merger and ringdown (IMR) of binary black holes: SEOBNRv4PHM. In the nonprecessing limit, the model reduces to SEOBNRv4HM, which was calibrated to numerical-relativity (NR) simulations, and waveforms from perturbation theory. We validate SEOBNRv4PHM by comparing it to the public catalog of 1405 precessing NR waveforms of the Simulating eXtreme Spacetimes (SXS) collaboration, and also to new 118 precessing NR waveforms, which span mass ratios 1-4 and spins up to 0.9. We stress that SEOBNRv4PHM is not calibrated to NR simulations in the precessing sector. We compute the unfaithfulness against the 1523 SXS precessing NR waveforms, and find that, for $94\%$ ($57\%$) of the cases, the maximum value, in the total mass range $20-200 M_\odot$, is below $3\%$ ($1\%$). Those numbers become $83\%$ ($20\%$) when using the IMR, multipolar, precessing phenomenological model IMRPhenomPv3HM. We investigate the impact of such unfaithfulness values with two parameter-estimation studies on synthetic signals. We also compute the unfaithfulness between those waveform models and identify in which part of the parameter space they differ the most. We validate them also against the multipolar, precessing NR surrogate model NRSur7dq4, and find that the SEOBNRv4PHM model outperforms IMRPhenomPv3HM.

Multipolar effective one body waveform model for spin-aligned black hole binaries

We introduce \TEOBiResumSM{}, an improved version of the effective-one-body (EOB) waveform model \TEOBResumS{} for spin-aligned, coalescing black hole binaries, that includes subdominant gravitational waveform modes completed through merger and ringdown. Beyond the dominant $(\ell,|m|)=(2,2)$ one, the more robust multipoles all over the parameter space are: $(2,1)$, $(3,3)$, $(3,2)$, $(4,4)$ and $(5,5)$. The multipolar ringdown EOB waveform stems from suitably fitting many numerical relativity (NR) waveform data from the Simulating eXtreme Spacetimes (SXS) collaboration together with test-mass waveform data. Mode-mixing effects are not incorporated. The orbital (nonspinning) part of the multipolar waveform amplitudes includes test-mass results up to (relative) 6PN order and, for most modes,is Pad\'e resummed. The $m$=odd waveform multipoles (up to $\ell=5$) incorporate most of the currently available spin-dependent analytical information. Improving on previous work, we confirm that certain $m=\text{odd}$ modes, e.g. the $(2,1)$, and even the $(3,1)$, may develop a zero (or a minimum) in the amplitude for nearly equal-mass binaries and for several combinations of the individual spins. A remarkable EOB/NR agreement around such zero is found for these modes. The new waveform, and radiation reaction, prompts a new NR-calibration of the spinning sector of the model, done with only $32$ datasets.The maximum $(2,2)$ EOB/NR unfaithfulness $\bar{F}$ with Advanced LIGO noise against the SXS catalog ($\sim 595$ datasets) is always below $0.5\%$ for binaries with total mass $M$ as $10M_\odot\leq M \leq 200M_\odot$, except for a single outlier with $\max{(\bar{F})}\sim 0.85\%$. When $(2,1)$, $(3,3)$ and $(4,4)$ modes are included, one finds an excellent EOB/NR agreement up to $M\sim 120M_\odot$, above which the performance degrades slightly and moves above $3\%$