Binary Black Hole System Research Articles

Outlook for detecting the gravitational-wave displacement and spin memory effects with current and future gravitational-wave detectors

Gravitational-wave memory effects arise from nonoscillatory components of gravitational-wave signals, and they are predictions of general relativity in the nonlinear regime that have close connections to the asymptotic properties of isolated gravitating systems. There are many types of memory effects that have been studied in the literature. In this paper we focus on the ``displacement'' and ``spin'' memories, which are expected to be the largest of these effects from sources such as the binary black hole mergers which have already been detected by LIGO and Virgo. The displacement memory is a change in the relative separation of two initially comoving observers due to a burst of gravitational waves, whereas the spin memory is a portion of the change in relative separation of observers with initial relative velocity. As both of these effects are small, LIGO, Virgo, and KAGRA can only detect memory effects from individual events that are much louder (and thus rarer) than those that have been detected so far. By combining data from multiple events, however, these effects could be detected in a population of binary mergers. In this paper, we present new forecasts for how long current and future detectors will need to operate in order to measure these effects from populations of binary black hole systems that are consistent with the populations inferred from the detections from LIGO and Virgo's first three observing runs. We find that a second-generation detector network of LIGO, Virgo, and KAGRA operating at the O4 (``design'') sensitivity for 1.5 years and then operating at the O5 (``plus'') sensitivity for an additional 1.5 years can detect the displacement memory. For Cosmic Explorer, we find that displacement memory could be detected for individual loud events, and that the spin memory could be detected in a population after 5 years of observation time.

New mechanisms for forming multiple hotspots in radio jets

ABSTRACTHotspots of radio galaxies are regions of shock-driven particle acceleration. Multiple hotspots have long been identified as potential indicators of jet movement or precession. Two frequent explanations describe a secondary hotspot as either the location of a prior jet termination point or a deflected backflow-driven shock: the so-called dentist’s drill and splatter-spot models. We created high-resolution simulations of precessing jets with a range of parameters. In addition to the existing mechanisms, our results show three additional mechanisms for multiple hotspot formation: (1) the splitting of a large terminal hotspot into passive and active components; (2) jet stream splitting resulting in two active hotspots; and (3) dynamic multiple hotspot complexes that form as a result of jet termination in a turbulent cocoon, linked here to rapid precession. We show that these distinct types of multiple hotspots are difficult to differentiate in synthetic radio maps, particularly hotspot complexes that can easily be mistaken for the jet itself. We discuss the implication for hypothesized binary supermassive black hole systems where jet precession is a key component of the morphology, and show a selection of potential precession candidates found using the Low-Frequency Array Two-metre Sky Survey Data Release 2.

Meet the Parents: The Progenitor Binary for the Supermassive Black Hole Candidate in E1821+643

The remnants of binary black hole mergers can be given recoil kick velocities up to 5000 km s−1 due to anisotropic emission of gravitational waves. E1821+643 is a recoiling supermassive black hole candidate with spectroscopically offset, broad emission lines, consistent with motion of the black hole at ∼2100 km s−1 along the line of sight relative to its host galaxy. This suggests a recoil kick of ∼2200 km s−1. Such a kick is powerful enough to eject E1821+643 from its M gal ∼ 2 × 1012 M ⊙ host galaxy. In this work, we address the question: assuming that E1821+643 is a recoiling black hole, what are the likely properties of the progenitor binary that formed E1821+643? Using astrophysically motivated priors, we infer that E1821+643 was likely formed from a binary black hole system with masses of , (90% credible intervals). Given our model, the black holes in this binary were likely to be spinning rapidly with dimensionless spin magnitudes of , . Such a high recoil velocity is impossible for spins aligned to the orbital angular momentum axis. This suggests that the progenitor for E1821+643 merged in hot gas, which is thought to provide an environment where spin alignment from accretion proceeds slowly relative to the merger timescale. We infer that E1821+643, if it is a recoiling black hole, is likely to be a rapidly rotating black hole with a dimensionless spin of χ = 0.92 ± 0.04. A 2.6 × 109 M ⊙ black hole, recoiling from a gas-rich environment at v ∼ 2200 km s−1, is likely to persist as an active galactic nucleus for ∼107 yr, in which time it traverses ∼25 kpc.

The Missing Link between Black Holes in High-mass X-Ray Binaries and Gravitational-wave Sources: Observational Selection Effects

There are few observed high-mass X-ray binaries (HMXBs) that harbor massive black holes (BHs), and none are likely to result in a binary black hole (BBH) that merges within a Hubble time; however, we know that massive merging BBHs exist from gravitational-wave (GW) observations. We investigate the role that X-ray and GW observational selection effects play in determining the properties of their respective detected binary populations. We find that, as a result of selection effects, detectable HMXBs and detectable BBHs form at different redshifts and metallicities, with detectable HMXBs forming at much lower redshifts and higher metallicities than detectable BBHs. We also find disparities in the mass distributions of these populations, with detectable merging BBH progenitors pulling to higher component masses relative to the full detectable HMXB population. Fewer than 3% of detectable HMXBs host BHs >35M ⊙ in our simulated populations. Furthermore, we find the probability that a detectable HMXB will merge as a BBH system within a Hubble time is ≃0.6%. Thus, it is unsurprising that no currently observed HMXB is predicted to form a merging BBH with high probability.

Morphology of Broad Emission Lines from Binary Supermassive Blackholes

Accretion onto a blackhole can indue extreme radiation stimulating emission lines in nearby gases. In the deep gravitational well, these clouds move at speeds up to 10,000 km/s, and so broadens the emission lines via the relativistic Doppler Effect. These broad emission lines on spectra are the most prominent feature of AGNs. The region around central black hole, where such broad emission lines are produced, is known as the broad-line region (BLR). We developed a self-consistent model to describe both the geometry of the BLR and the dynamics of the gas clouds in the BLR. The motion of clouds is described by a series of Keplerian orbits. The spectral shift of emission line can be derived by the radial velocity at each point in Keplerian orbits. Assuming that the BLR is stable, that is, the structure and distribution of gas in BLR doesn’t change over a considerable period of time, the accumulated emission line profile can be constructed by simple addition of all Keplerian orbits in the BLR. By comparing the calculated profiles to spectra observed in SDSS (Sloan Digital Sky Survey), we found that our model can satisfactorily match most observed profiles. We attempted to review and summarize potential binary AGNs. We applied the model to the study of binary AGNs and their profiles of emission lines. We considered the velocity offset due to mutual Keplerian motion of black holes in binary and added their respective profiles to produce the final, resulting emission line profile from binary AGNs. Three kinds of emission line profiles are featured in our simulations: twin-peak structures where two strong broad-lines are present; sub-peak structures where a smaller but still visible emission line accompanies the dominant line; single broad emission peak but with significant velocity offset from the systematic redshift that is derived from the narrow emission-lines on the same spectrum. We then analyzed 1,348 AGN spectra with high S/N ratio in SDSS database, and selected 26 as candidate binary supermassive blackhole systems. These candidates are valuable for following-up observation, their binary nature could be confirmed by detecting the profile variation due to orbital motions.

A Numerical Investigation of Tidal Disruption Rate Enhancement in Post-Starburst galaxies

Tidal disruption is an uncommon but important phenomenon that occurs when a star’s gravity is overcome by that of the SMBH which it is orbiting. In this process, researchers may gleam various properties of the host galaxy’s nucleic region, such as the accretion process, debris fallback, behavior of active galactic nuclei and quasars, etc. In this work we present a numerical analysis of TDE rates using the loss cone theory, a leading theoretical picture in this field, based on changes to several pivotal variables, such as SMBH mass, stellar mass, velocity dispersion etc. We then extend this to fit the profiles of E+A post starburst galaxies and the occasion of binary black hole systems.

Numerical-relativity surrogate modeling with nearly extremal black-hole spins

Numerical relativity (NR) simulations of binary black hole (BBH) systems provide the most accurate gravitational wave predictions, but at a high computational cost—especially when the black holes have nearly extremal spins (i.e. spins near the theoretical upper limit) or very unequal masses. Recently, the technique of reduced order modeling has enabled the construction of ‘surrogate models’ trained on an existing set of NR waveforms. Surrogate models enable the rapid computation of the gravitational waves emitted by BBHs. Typically these models are used for interpolation to compute gravitational waveforms for BBHs with mass ratios and spins within the bounds of the training set. Because simulations with nearly extremal spins are so technically challenging, surrogate models almost always rely on training sets with only moderate spins. In this paper, we explore how well surrogate models can extrapolate to nearly extremal spins when the training set only includes moderate spins. For simplicity, we focus on one-dimensional surrogate models trained on NR simulations of BBHs with equal masses and equal, aligned spins. We assess the performance of the surrogate models at higher spin magnitudes by calculating the mismatches between extrapolated surrogate model waveforms and NR waveforms, by calculating the differences between extrapolated and NR measurements of the remnant black-hole mass, and by testing how the surrogate model improves as the training set extends to higher spins. We find that while extrapolation in this one-dimensional case is viable for current detector sensitivities, surrogate models for next-generation detectors should use training sets that extend to nearly extremal spins.

Ultra high vacuum beam pipe of the Einstein Telescope project: Challenges and perspectives

The Einstein Telescope (ET) is a project aiming to realize a facility to host a gravitational wave (GW) detector of the third generation. The new instrument will change our vision of the Universe by observing millions of GW signals emitted during the coalescence of stellar and intermediate-mass black hole binary systems. It will permit to shed light on the first phase of the Universe formation and it will contribute to solving the dark matter enigma. The new GW detector is conceived as a series of six nested Michelson interferometers forming a triangle of 10 km side. The laser light biasing the interferometers must propagate in large ultra-high vacuum (UHV) tubes in order to reduce the noise induced by the residual gas pressure fluctuations, setting a requirement on the residual pressure in the 10−10 mbar range. The vacuum system will be made of a pipe with a 1 m diameter and an overall length of 120 km, making ET one of the largest UHV systems ever made. The giant UHV project asks for attentive optimization of material choice, manufacturing processes, post-processing treatments of the tubes, and pumping systems in order to find a cost-effective solution. In this article, we shortly review the vacuum solution adopted in the case of the second generation of GW detectors. After a general description of the main elements that constitute the ET vacuum system, the detailed design being the subject of the next 3 years of work, we will present a refined calculation of the noise due to residual-gas pressure fluctuations in the ET beam pipe.

A Special State Transition in the Blazar OT 081: Implication for the Unified State Transition Paradigm of Different-scale Black Hole Systems

Exploring the similar behavior of black hole systems with different scales will provide insight into the unified physical laws of black hole systems. Here, we report a special spectral state transition process in blazar OT 081, which is driven by a supermassive black hole. Based on the X-ray flux versus photon index distribution, stacked average X-ray spectra, L 2500Å − α ox parameters, and broadband spectral energy distributions, we conducted a pilot study on the spectral state transition for this blazar system. The analysis results suggest that the source transitions through a steady-state point from a strong corona, weak jet unsteady state to a weak corona, strong jet unsteady state. This state transition behavior is similar to that observed in the much smaller Galactic black hole binary systems, providing further observational evidence for the possible existence of a unified state transition paradigm for black hole systems with different scales.

A Calabi–Yau threefold coming from two black holes

In this paper, we show that a set of six square roots of homogeneous polynomials in four variables, related to a binary system of black holes studied by Stefan Weinzierl, is not rationalizable. We prove it by showing that the variety X associated to the product of four of the six square roots is not unirational. In particular, we show that the smooth model of X is a Calabi–Yau threefold.

Nonlinear studies of binary black hole mergers in Einstein-scalar-Gauss-Bonnet gravity

We study the nonlinear dynamics of binary black hole systems with scalar charge by numerically evolving the full equations of motion for shift-symmetric Einstein scalar Gauss-Bonnet gravity. We consider quasi-circular binaries with different mass-ratios, varying the Gauss-Bonnet coupling and quantifying its impact on the emitted scalar and gravitational waves. We compare our numerical results to post-Newtonian calculations of the radiation emitted during the inspiral. We demonstrate the accuracy of the leading-order terms in post-Newtonian theory in modeling the amplitude of the scalar waveform, but find that, at least for the last few orbits before merger, the currently available post-Newtonian theory is not sufficient to model the dephasing of the gravitational wave signal in this theory. We further find that there is non-negligible nonlinear enhancement in the scalar field at merger, but that the effect on the peak gravitational wave emission is small.

Quasi-periodic behaviour in the radio and γ-ray light curves of blazar PKS 1510–089

Abstract We explore the possible quasi-periodic oscillations (QPOs) of the blazar PKS 1510–089, utilizing the ∼38-year Metsähovi flux density observations at 37 GHz and over ten-year Fermi-LAT observations in the 0.1–300 GeV energy range. Both the flux distributions of the radio and γ-ray light curves suggest a log-normal distribution, and power spectral densities (PSDs) of both light curves can be well represented by a bending power-law model. Comparing the results from the Weighted Wavelet Z-transform and Lomb-Scargle Periodogram approaches, a quasi period of 1330 ± 55 days at a 99.80% (>3σ) significance against the red noise background is observed in the radio light curve, whereas no similar modulation is seen in the γ-ray light curve. We briefly discuss the research actuality of blazar QPO phenomena and explain the observed radio QPO as the result of Keplerian motion in a supermassive binary black hole system and periodic modulation induced by the Lense-Thirring precession of the innermost portions of the accretion disk.

Relativistic scenario for a binary black hole system in blazars

AbstractBlazars are a type of active galactic nuclei whose jet points toward the observer. Their emission is variable along different time scales and at different wavelengths. Some objects show periodicity in their emission, like the blazar PG 1553+113. In this work, we obtain a periodicity of ∼2.19 years using 12.5 years of data of Fermi‐LAT and then we study a scenario to explain blazar periodicities with timescales of a few years. The scenario is built on a binary supermassive black hole (SMBHs) system where one of the two SMBHs carries a jet. We also assume that one of the two SMBHs has angular momentum and is described by a Kerr metric. We have found estimates for the masses of the sources and the distance separating the two SMBHs.

Eccentric binary black holes: Comparing numerical relativity and small mass-ratio perturbation theory

The modeling of unequal mass binary black hole systems is of high importance to detect and estimate parameters from these systems. Numerical relativity (NR) is well suited to study systems with comparable component masses, ${m}_{1}\ensuremath{\sim}{m}_{2}$, whereas small mass ratio (SMR) perturbation theory applies to binaries where $q={m}_{2}/{m}_{1}\ensuremath{\ll}1$. This work investigates the applicability for NR and SMR as a function of mass ratio for eccentric nonspinning binary black holes. We produce 52 NR simulations with mass ratios between $1:10$ and $1:1$ and initial eccentricities up to 0.8. From these we extract quantities like gravitational wave energy and angular momentum fluxes and periastron advance, and assess their accuracy. To facilitate comparison, we develop tools to map between NR and SMR inspiral evolutions of eccentric binary black holes. We derive post-Newtonian accurate relations between different definitions of eccentricity. Based on these analyses, we introduce a new definition of eccentricity based on the (2,2)-mode of the gravitational radiation, which reduces to the Newtonian definition of eccentricity in the Newtonian limit. From the comparison between NR simulations and SMR results, we quantify the unknown next-to-leading order SMR contributions to the gravitational energy and angular momentum fluxes, and periastron advance. We show that in the comparable mass regime these contributions are subdominant and higher order SMR contributions are negligible.

Research on a 3.7-year Quasi-periodic Oscillation for FSRQ J0351-1153

From the Owens Valley Radio Observatory 40 m radio telescope, we have collected the light curves of the 15 GHz radio band for FSRQ J0153-1153, spanning from 2009 February to 2018 February. The Lomb–Scargle Periodogram method and the Weighted Wavelet Z-transform method are employed to search for the quasi-periodic oscillation (QPO) signal of these data, and the simulation method for the light curve is utilized to estimate the significance level of this QPO signal; thus through these techniques, the QPO signal of 3.7 ± 0.5 yr with a significance level of 3.68σ is revealed for the first time. It is most likely an explanation for the QPO signal that a binary black hole system gives rise to a Newtonian-driven the precession of jet. Based on this assumption, we find that the mass of the secondary black hole in this system may be larger than the mass of the primary black hole; and we estimate the intrinsic QPO of jet precession and the QPO of companion star orbit.

Gamma‐ray production in supermassive black hole binary OJ 287

AbstractOJ 287 is one of the most studied BL Lac objects with very long optical measurements whose spectrum has been well measured through radio to X‐ray band. The most outstanding characteristic of OJ 287 is its 12‐year period, which is discovered in the optical range and has also been confirmed in the X‐ray band. OJ 287 is supposed to be a binary black hole system in which a secondary black hole passes the accretion disk of the primary black hole and produces two impact flashes per period. It has also been proposed to be a GeV–TeV source. Observations of OJ 287 in the GeV–TeV energy range reveal the variable γ‐ray connected with the flare activity of this object. The spectral energy distributions of blazars consist of two broad peaks. The first, lower frequency peak is due to the synchrotron emissions of relativistic electrons in the jet. Leptonic and hadronic emission mechanisms are considered to describe the second, higher frequency spectrum part. The inverse Compton emissions of the same electrons (synchrotron self‐Compton model) or combined with an external Compton mechanism are considered in the leptonic scenario. The last one supposes the existence of the external to jet photon cloud. The high‐energy spectrum part is also supposed to be generated due to the acceleration of the cosmic ray hadrons in shock produced by outflow, which expands and then collides with the wind of the primary black hole. The detection of GeV–TeV energy fluxes can help find the parameters of the configuration of the two‐black hole system.

Nanohertz gravitational wave astronomy during SKA era: An InPTA perspective

Decades long monitoring of millisecond pulsars, which exhibit highly stable rotational periods in pulsar timing array experiments is on the threshold of discovering nanohertz stochastic gravitational wave background. This paper describes the Indian pulsar timing array (InPTA) experiment, which employs the upgraded Giant Metrewave Radio Telescope (uGMRT) for timing an ensemble of millisecond pulsars for this purpose. We highlight InPTA’s observation strategies and analysis methods, which are relevant for a future PTA experiment with the more sensitive Square Kilometer Array (SKA) telescope. We show that the unique multi-sub-array multi-band wide-bandwidth frequency coverage of the InPTA, provides dispersion measure estimates with unprecedented precision for PTA pulsars, e.g., \(\sim 2 \times 10^{-5}\) pc cm\(^{-3}\) for PSR J1909-3744. Configuring the SKA-low and SKA-mid as two and four sub-arrays, respectively, it is shown that comparable precision is achievable, using observation strategies similar to those pursued by the InPTA, for a larger sample of 62 pulsars, requiring about 26 and 7 h per epoch for the SKA-mid and the SKA-low telescopes, respectively. We also review the ongoing efforts to develop PTA-relevant general relativistic constructs that will be required to search for nanohertz gravitational waves from isolated super-massive black hole binary systems like blazar OJ 287. These efforts should be relevant to pursue persistent multi-messenger gravitational wave astronomy during the forthcoming era of the SKA telescope, the thirty meter telescope, and the next-generation event horizon telescope.

Swift J1728.9−3613 is a black hole X-ray binary: a spectral and timing study usingNICER

ABSTRACTWe have studied different timing and spectral properties of the new Galactic X-ray transient Swift J1728.9−3613 using NICER and Swift, discovered by the Burst Alert Telescope on the Neil Gehrels Swift Observatory. The source went through multiple transitions to different spectral states during the outburst, and the complete evolution created a ‘q’-shaped track in the hardness-intensity diagram. A partial hysteresis is also observed in the RMS-intensity diagram, which is another well-defined feature of black hole transients. In soft intermediate states, power-density spectra were dominated by broad-band noise components, and two type-B quasi-periodic oscillations were detected. We have fitted 1–10 keV energy spectra obtained from NICER observations that were performed during the outburst, and the temporal evolution of spectral parameters is studied. A small-scale reflare happened near MJD 58584.69, resulting in finite changes in spectral parameters, and the 1–10 keV averaged flux also increased. We observed that the innermost radius of the accretion disc was almost constant during the soft state and we have measured the mass of the compact object to be ∼4.6 M⊙, considering a non-spinning black hole binary system. The soft-to-hard transition occurred when the bolometric luminosity was 0.01 times the Eddington luminosity. Based on our combined study of the evolution of the timing and spectral properties, we conclude that the new source Swift J1728.9−3613 is a black hole X-ray binary.

Wormholes, killing horizons and naked singularities: light surfaces in axially symmetric spacetimes

We study several classes of exterior and interior axially symmetric spacetimes, such as wormholes, accelerating black holes, and binary black hole systems, from the point of view of light surfaces related to the generators of Killing horizons. We show that light surfaces constitute a useful framework for the study of the more diverse axially symmetric geometries. In particular, we point out the existence of common properties of the light surfaces in different spacetimes. We introduce a deformation of the Kerr–Newman metric and apply the light surfaces framework to analyze several generalizations in a compact form. As particular examples, we analyze static and spinning wormhole solutions, black holes immersed in external (perfect fluid) dark matter, spacetimes with (Taub) NUT charge, acceleration, magnetic charge, and cosmological constant, binary Reissner–Nordström black holes, a solution of a (low-energy effective) heterotic string theory, and the (1+2) dimensional BTZ geometry.

Evidence for a milliparsec-separation supermassive binary black hole with quasar microlensing

We report periodic oscillations in the 15-year-long optical light curve of the gravitationally lensed quasar Q J0158−4325 at zs = 1.29. The signal is enhanced during a high magnification microlensing event of the quasar that the fainter lensed image, B, underwent between 2003 and 2010. We measure a period of Po = 172.6 ± 0.9 days, which translates to 75.4 ± 0.4 days in the quasar frame. The oscillations have a maximum amplitude of 0.26 ± 0.02 mag and decrease concurrently with the smooth microlensing amplitude. We explore four scenarios to explain the origin of the periodicity: (1) the high magnification microlensing event is due to a binary star in the lensing galaxy, (2) Q J0158−4325 contains a supermassive binary black hole system in its final dynamical stage before merging, (3) the quasar accretion disk contains a bright inhomogeneity in Keplerian motion around the black hole, and (4) the accretion disk is in precession. Of these four scenarios, only a supermassive binary black hole can account for both the short observed period and the amplitude of the signal, through the oscillation of the accretion disk towards and away from high-magnification regions of a microlensing caustic. The short measured period implies that the semi-major axis of the orbit is ∼10−3 pc and that and the coalescence timescale is tcoal ∼ 1000 yr, assuming that the decay of the orbit is solely powered by the emission of gravitational waves. The probability of observing a system so close to coalescence, in a sample of only 30 monitored lensed quasars, suggests either a much larger population of supermassive binary black holes than predicted or, more likely, that some other mechanism significantly increases the coalescence timescale. Three tests of the binary black hole hypothesis include: (i) the recurrence of oscillations in photometric monitoring during any future microlensing events in either image, (ii) spectroscopic detection of Doppler shifts (up to ∼0.01c) associated with optical emission in the vicinity of the black holes, and (iii) the detection of gravitational waves through pulsar timing array experiments, such as the Square Kilometre Array, which will have the sensitivity to detect the ∼100 nano-hertz emission.