General relativistic simulations of the quasi-circular inspiral and merger of charged black holes: GW150914 and fundamental physics implications

We perform general-relativistic simulations of charged black holes targeting GW150914. We show that the inspiral is most efficient for detecting black hole charge through gravitational waves and that GW150914 is compatible with having charge-to-mass ratio as high as 0.3. Our work applies to electric and magnetic charge, and to theories with black holes endowed with U(1) (hidden or dark) charges. Using our results we place an upper bound on the deviation from general relativity in the dynamical, strong-field regime of the so-called theory of MOdified Gravity (MOG).Comment: 10 pages (including Supplemental Material), 3 figures. Matches published versio

Can quasi-circular mergers of charged black holes produce extremal black holes?

In contrast to energy and angular momentum, electric charge is conserved in mergers of charged black holes. This opens up the possibility for the remnant to have Kerr-Newman parameter $\chi^{2} + \lambda^{2}$ greater than 1 (with $\chi$ and $\lambda$ being the black hole dimensionless spin and dimensionless charge, respectively), which is forbidden by the cosmic censorship conjecture. In this paper, we investigate whether a naked singularity can form in quasi-circular mergers of charged binary black holes. We extend a theoretical model to estimate the final properties of the remnant left by quasicircular mergers of binary black holes to the charged case. We validate the model with numerical-relativity simulations, finding agreement at the percent level. We then use our theoretical model to argue that while naked singularities cannot form following quasi-circular mergers of non-spinning charged binary black holes, it is possible to produce remnants that are arbitrarily close to the extremal limit.Comment: 7 pages, 2 figures, code availabl

Initial data for general relativistic simulations of multiple electrically charged black holes with linear and angular momenta

A general relativistic, stationary and axisymmetric black hole in a four-dimensional asymptotically-flat spacetime is fully determined by its mass, angular momentum and electric charge. The expectation that astrophysically relevant black holes do not posses charge has resulted in a limited number of investigations of moving and charged black holes in the dynamical, strong-field gravitational (and electromagnetic) regime, where numerical studies are necessary. Apart from having a theoretical interest, the advent of multimessenger astronomy with gravitational waves offers new ways to think about charged black holes. In this work, we initiate an exploration of charged binary black holes by generating valid initial data for general relativistic simulations of black hole systems that have generic electric charge, linear and angular momenta. We develop our initial data formalism within the framework of the conformal transverse-traceless (Bowen-York) technique using the puncture approach, and apply the theory of isolated horizons to attribute physical parameters (mass, charge and angular momentum) to each hole. We implemented our formalism in the case of a binary system by modifying the publicly available TwoPunctures and QuasiLocalMeasures codes. We demonstrate that our code can recover existing solutions and that it has excellent self-convergence properties for a generic configuration of two black holes.Comment: 18 pages, 6 figures. Rev 2 fixes typos and adds minor clarification

Maximum mass and universal relations of rotating relativistic hybrid hadron-quark stars

We construct equilibrium models of uniformly and differentially rotating hybrid hadron-quark stars using equations of state (EOSs) with a first-order phase transition that gives rise to a third family of compact objects. We find that the ratio of the maximum possible mass of uniformly rotating configurations - the supramassive limit - to the Tolman-Oppenheimer-Volkoff (TOV) limit mass is not EOS-independent, and is between 1.15 and 1.31,in contrast with the value of 1.20 previously found for hadronic EOSs. Therefore, some of the constraints placed on the EOS from the observation of the gravitational wave event GW170817 do not apply to hadron-quark EOSs. However, the supramassive limit mass for the family of EOSs we treat is consistent with limits set by GW170817, strengthening the possibility of interpreting GW170817 with a hybrid hadron-quark EOSs. We also find that along constant angular momentum sequences of uniformly rotating stars, the third family maximum and minimum mass models satisfy approximate EOS-independent relations, and the supramassive limit of the third family is approximately 16.5 % larger than the third family TOV limit. For differentially rotating spheroidal stars, we find that a lower-limit on the maximum supportable rest mass is 123 % more than the TOV limit rest mass. Finally, we verify that the recently discovered universal relations relating angular momentum, rest mass and gravitational mass for turning-point models hold for hybrid hadron-quark EOSs when uniform rotation is considered, but have a clear dependence on the degree of differential rotation.Comment: 19 pages, 14 figures, submitted to EPJA Topical Issue "First joint gravitational wave and electromagnetic observations: Implications for nuclear and particle physics

Quantifying uncertainties in general relativistic magnetohydrodynamic codes

In this paper, we show that similar open-source codes for general relativistic magnetohydrodynamic (GRMHD) produce different results for key features of binary neutron star mergers. First, we present a new open-source version of the publicly available IllinoisGRMHD code that provides support for realistic, finite temperature equations of state. After stringent tests of our upgraded code, we perform a code comparison between GRHydro, IllinoisGRMHD, Spritz, and WhiskyTHC, which implement the same physics, but slightly different computational methods. The benefit of the comparison is that all codes are embedded in the EinsteinToolkit suite, hence their only difference is algorithmic. We find similar convergence properties, fluid dynamics, and gravitational waves, but different merger times, remnant lifetimes, and gravitational wave phases. Such differences must be resolved before the post-merger dynamics modeled with such simulations can be reliably used to infer the properties of nuclear matter especially in the era of precision gravitational wave astronomy

Kicks in charged black hole binaries

We compute the emission of linear momentum (kicks) by both gravitational and electromagnetic radiation in fully general-relativistic numerical evolutions of quasi-circular charged black hole binaries. We derive analytical expressions for slowly moving bodies and explore numerically a variety of mass ratios and charge-to-mass ratios. We find that for the equal mass case our analytical expression is in excellent agreement with the observed values and, contrarily to what happens in the vacuum case, we find that in presence of electromagnetic fields there is emission of momentum by gravitational waves. We also find that the strong gravitational kicks of binaries with unequal masses affect the electromagnetic kicks, causing them to strongly deviate from Keplerian predictions. For the values of charge-to-mass ratio considered in this work, we observe that magnitudes of the electromagnetic kicks are always smaller than the gravitational ones.publishe

Electromagnetic Fields and Radiation in Dynamical Spacetimes

In this dissertation, I present the development and application of new mathematical and computational tools to study dynamical spacetimes with extreme gravitational and electromagnetic fields. I discuss and implement a formalism to generate initial data for general relativistic simulations of generic black hole configurations with charge. I introduce techniques to obtain stable quasi-circular inspirals and mergers and I perform the first simulations of this kind. I use these results to place the first constraint on the charge of astrophysical black holes and on specific modified theories of gravity using the gravitational wave event GW150914. I present and benchmark approximate methods to study these systems and derive an analytical technique to estimate the properties of the remnant left by a merger of charged black holes. I investigate ultra-relativistic collisions of charged binaries and discuss their implications for a variety of conjectures in theoretical and fundamental physics. I argue that in the full non-linear theory, neither ultra-relativistic collisions nor quasi-circular inspiral can overcharge a black hole and produce a naked singularity. Finally, I present new software for numerical relativity, including a novel code to perform ray tracing and radiation transfer. I use this code to describe some subtle features of general relativistic ray tracing

Black Hole Physics and Computer Graphics

Black holes are among the most extreme objects known to exist. As such, they are excellent laboratories for testing fundamental theories and studying matter in conditions that cannot be found anywhere else. In this article, we highlight the relevance of black holes in modern physical research and present a way to advance our understanding with numerical simulations. We briefly review dynamical-spacetime General-Relativistic-Magneto-HydroDynamic (GRMHD) calculations as fundamental tools to study the local properties of black holes and matter around them. Then, we discuss the need for general-relativistic radiation-transport to propagate the local information about light obtained with GRMHD simulations to our telescopes. Finally, we present our work on accretion onto binary black holes. The goal of our paper is to introduce the reader to some of the methods in current black hole research and to show how improvements in hardware and software for computer graphics support advancements in the field.Astrophysics Science DivisionImmediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]