Binary Black Hole System Research Articles

Self-interacting axion clouds around rotating black holes in binary systems

Self-interacting axion clouds around rotating black holes in binary systems

AT 2021hdr: A candidate tidal disruption of a gas cloud by a binary super massive black hole system

With a growing number of facilities able to monitor the entire sky and produce light curves with a cadence of days, in recent years there has been an increased rate of detection of sources whose variability deviates from standard behavior, revealing a variety of exotic nuclear transients. The aim of the present study is to disentangle the nature of the transient AT\,2021hdr, whose optical light curve used to be consistent with a classic Seyfert 1 nucleus, which was also confirmed by its optical spectrum and high-energy properties. From late 2021, AT\,2021hdr started to present sudden brightening episodes in the form of oscillating peaks in the Zwicky Transient Facility (ZTF) alert stream, and the same shape is observed in X-rays and UV from Swift data. The oscillations occur every sim 60-90 days with amplitudes of sim 0.2 mag in the g and r bands. Very Long Baseline Array (VLBA) observations show no radio emission at milliarcseconds scale. It is argued that these findings are inconsistent with a standard tidal disruption event (TDE), a binary supermassive black hole (BSMBH), or a changing-look active galactic nucleus (AGN); neither does this object resemble previous observed AGN flares, and disk or jet instabilities are an unlikely scenario. Here, we propose that the behavior of AT\,2021hdr might be due to the tidal disruption of a gas cloud by a BSMBH. In this scenario, we estimate that the putative binary has a separation of sim 0.83 mpc and would merge in sim 7times 10$^4$ years. This galaxy is located at 9 kpc from a companion galaxy, and in this work we report this merger for the first time. The oscillations are not related to the companion galaxy.

Systematic bias due to mismodeling precessing binary black hole ringdown

Accurate waveform modeling is crucial for parameter estimation in gravitational wave astronomy, impacting our understanding of source properties and the testing of general relativity. The precession of orbital and spin angular momenta in binary black hole (BBH) systems with misaligned spins presents a complex challenge for gravitational waveform modeling. Current precessing BBH waveform models employ a coprecessing frame, which precesses along with the binary. In this paper, we investigate a source of bias stemming from the mismodeling of ringdown frequency in the coprecessing frame. We find that this mismodeling of the coprecessing frame ringdown frequency introduces systematic biases in parameter estimation, for high-mass systems in particular, and in the inspiral-merger-ringdown (IMR)-consistency test of general relativity. Employing the waveform model henom, we conduct an IMR-consistency test using a Fisher matrix analysis across parameter space, as well as full injected signal parameter estimation studies. Our results show that this mismodeling particularly affects BBH systems with high-mass ratios, high-spin magnitudes, and highly inclined spins. These findings suggest inconsistencies for all waveform models which do not address this issue. Published by the American Physical Society 2024

Detection of gravitational wave signals from precessing binary black hole systems using convolutional neural networks

Detection of gravitational wave signals from precessing binary black hole systems using convolutional neural networks

The Detection of Possible Quasiperiodic Oscillations in the BL Lac 4FGL J2139.4−4235

We present periodicity search analyses on the long-term γ-ray light curve of the BL Lacertae object 4FGL J2139.4−4235 observed by the Fermi Large Area Telescope, over a period of more than 15 yr, from 2008 August 4 to 2023 December 10. To determine the quasiperiodic oscillation (QPO) behavior of 4FGL J2139.4−4235 in the 0.3–300 GeV energy range, we used four methods, namely the Lomb–Scargle periodogram, the weighted wavelet z-transform, the phase dispersion minimization, and the autoregressive integrated moving average model. A Monte Carlo simulation technique is used to evaluate the significance level of the QPO signal. Significant levels above 3.5σ were detected in the γ-ray light curve at about 650 days QPO, which is presented throughout the observation period. Interestingly, there was some correlation between the three bands in the discrete correlation function method calculations, which may be an indication that the variability trends between the three bands are similar. We explore the possible physical models and show that a supermassive binary black hole system or a jet helical motion model seem to be reasonable explanations for the potential QPO behavior.

Circumbinary Disk Spectra Irradiated by Two Central Accretion Disks in a Binary Black Hole System

We study the effect of irradiation from two accretion disks (minidisks) around respective black holes of stellar-to-intermediate masses in a circular binary on the spectrum of a circumbinary disk (CBD) surrounding them. We assume the CBD to be a standard disk and adopt the orbit-averaged irradiation flux because the viscous timescale is much longer than the orbital period. We then solve the energy equation both analytically and numerically to compute the CBD temperature distribution and the corresponding disk spectrum. We find that the analytically calculated spectra are in good agreement with the numerical ones. The CBD spectrum is almost independent of the binary mass ratio. We also find that the combined spectra of two minidisks and the CBD have double peaks, one peak in the soft X-ray band and the other in the infrared (IR) band. The former peak comes from the two minidisks, while the latter peak from the CBD. The observed flux density increases with frequency as ν 1/3 toward the soft X-ray peak, while it decreases with frequency away from the IR peak as ν −5/3. The latter feature is testable with near-IR observations with Subaru and JWST.

Hydrodynamic 3D Simulation of Roche Lobe Overflow in High-mass X-Ray Binaries

Abstract While binary merger events have been an active area of study in both simulations and observational work, the formation channels by which a high-mass star extends from Roche lobe overflow (RLO) in a decaying orbit of a black-hole (BH) companion to a binary black-hole (BBH) system merits further investigation. Variable length-scales must be employed to accurately represent the dynamical fluid transfer and morphological development of the primary star as it conforms to a diminishing Roche lobe under the runaway influence of the proximal BH. We have simulated and evolved binary mass flow under these conditions to better identify the key transitional processes from RLO to BBHs. We demonstrate a new methodology to model RLO systems to unprecedented resolution simultaneously across the envelope, donor wind, tidal stream, and accretion disk regimes without reliance upon previously universal symmetry, mass flux, and angular momentum flux assumptions. We have applied this method to the semidetached high-mass X-ray binary M33 X-7 in order to provide a direct comparison to recent observations of an RLO candidate system at two overflow states of overfilling factors f = 1.01 and f = 1.1. We found extreme overflow (f = 1.1) to be entirely conservative in both mass and angular momentum transport, forming a conical L1 tidal stream of density and deflected angle comparable to existing predictions. This case lies within the unstable mass transfer (MT) regime as recently proposed of M33 X-7. The f = 1.01 case differed in stream geometry, accretion disk size, and efficiency, demonstrating nonconservative stable MT through a ballistic uniform-width stream. The nonconservative and stable nature of the f = 1.01 case MT also suggests that existing assumptions of semidetached binaries undergoing RLO may mischaracterize their role and distribution as progenitors of BBHs and common envelopes.

Optical and γ-ray variability analysis of BL Lacertae object TXS 1902+556

ABSTRACT The variability data for the BL Lacertae object TXS 1902+556 in the optical and $\gamma$-ray wavebands were obtained from the 0.76-m Katzman Automatic Imaging Telescope and the Fermi Large Area Telescope (Fermi-LAT), covering periods of 14.4 and 14.7 yr, respectively. The variability properties were systematically analysed, with particular emphasis on the first comprehensive investigation of radiation variation in the optical waveband. Four well-established techniques were employed for this purpose: the Lomb–Scargle periodogram, REDFIT program, Jurkevich method, and discrete correlation function (DCF) approach. The optical waveband exhibits quasi-periodic oscillations (QPO) with a time-scale of $P_{\rm O}=276.8\pm 6.1$ d at a significance level $3.87\sigma$, while the $\gamma$-ray waveband does not exhibit any significant periodicity. However, it should be noted that the QPO time-scale is consistent with the Sun-gaps in the optical light curve within 2$\sigma$ uncertainties. The optical QPO behaviour is most likely attributed to the helical motion of the jet driven by the orbital motion in a supermassive black hole binary system. Moreover, we have provided an explanation for the absence of QPO in the $\gamma$-ray light curves. Furthermore, utilizing the DCF method, a weak correlation between the variability in the optical and $\gamma$-ray wavebands was observed, suggesting that the emission of TXS 1902+556 may be generated through a combination of synchrotron self-Compton (SSC) and external Compton (EC) processes, or a leptonic–hadronic hybrid process.

Discovery of persistent quasi-periodic oscillations in accreting white dwarfs: a new link to X-ray binaries

ABSTRACT Almost all accreting black hole and neutron star (NS) X-ray binary systems (XRBs) exhibit prominent brightness variations on a few characteristic time-scales and their harmonics. These quasi-periodic oscillations (QPOs) are thought to be associated with the precession of a warped accretion disc, but the physical mechanism that generates the precessing warp remains uncertain. Relativistic frame dragging (Lense–Thirring precession) is one promising candidate, but a misaligned magnetic field is an alternative, especially for NS XRBs. Here, we report the discovery of five accreting white dwarf systems (AWDs) that display strong optical QPOs with characteristic frequencies and harmonic structures that suggest they are the counterpart of the QPOs seen in XRBs. Since AWDs are firmly in the classical (non-relativistic) regime, Lense–Thirring precession cannot account for these QPOs. By contrast, a weak magnetic field associated with the white dwarf can drive disc warping and precession in these systems, similar to what has been proposed for NS XRBs. Our observations confirm that magnetically driven warping is a viable mechanism for generating QPOs in disc-accreting astrophysical systems, certainly in AWDs and possibly also in NS XRBs. Additionally, they establish a new way to estimate magnetic field strengths, even in relatively weak-field systems where other methods are not available.

Detection of the Fe K lines from the binary AGN in 4C+37.11

We report the discovery of the Fe K line emission at $ $ keV with a width of $ $ keV using two epochs of Chandra archival data for the nucleus of the galaxy 4C+37.11, which is known to host a binary supermassive black hole (BSMBH) system where the SMBHs are separated by $ mas or sim 7pc. Our study reports the first detection of the Fe K line from a known binary AGN, which has an F-statistic value of 20.98 and a probability of $2.47 $. Stacking two spectra reveals another Fe K line component at $ $ keV. Different model scenarios indicate that the lines originate from the combined effects of accretion disk emission and circumnuclear collisionally ionized medium. The observed low column density favors a gas-poor merger scenario, where the high temperature of the hot ionized medium may be associated with the shocked gas in the binary merger and not with star formation activity. The estimated total BSMBH mass and disk inclination are $ $ M$_ and $ indicating that the BSMBH is probably a high-inclination system. We were not able to tightly constrain the spin parameter using the present data sets. Our results draw attention to the fact that detecting the Fe K line emissions from BSMBHs is important for estimating the individual SMBH masses and the spins of the binary SMBHs, as well as for exploring their emission regions.

Delayed Emission from Luminous Blue Optical Transients in Black Hole Binary Systems

At least three members of the recently identified class of fast luminous blue optical transients show evidence of late-time electromagnetic activity in great excess of what was predicted by an extrapolation of the early time emission. In particular, AT2022tsd displays fast, bright optical fluctuations approximately a month after the initial detection. Here we propose that these transients are produced by exploding stars in black hole binary systems and that the late-time activity is due to the accretion of clumpy ejecta onto the companion black hole. We derive the energetics and timescales involved, compute the emission spectrum, and discuss whether the ensuing emission is diffused or not in the remnant. We find that this model can explain the observed range of behaviors for reasonable ranges of the orbital separation and the ejecta velocity and clumpiness. Close separation and clumpy, high-velocity ejecta result in bright variable emission, as seen in AT2022tsd. A wider separation and smaller ejecta velocity, conversely, give rise to fairly constant emission at a lower luminosity. We suggest that high-cadence, simultaneous, panchromatic monitoring of future transients should be carried out to better understand the origin of the late emission and the role of binarity in the diversity of explosive stellar transients.

Eccentricity Estimation for Five Binary Black Hole Mergers with Higher-order Gravitational-wave Modes

The detection of orbital eccentricity for a binary black hole system via gravitational waves is a key signature to distinguish between the possible binary origins. The identification of eccentricity has been difficult so far due to the limited availability of eccentric gravitational waveforms over the full range of black hole masses and eccentricities. Here we evaluate the eccentricity of five black hole mergers detected by the LIGO and Virgo observatories using the TEOBResumS-DALI, TEOBResumS-GIOTTO, and TEOBResumSP models. This analysis studies eccentricities up to 0.6 at the reference frequency of 5 Hz and incorporates higher-order gravitational-wave modes critical to model emission from highly eccentric orbits. The binaries have been selected due to previous hints of eccentricity or due to their unusual mass and spin. While other studies found marginal evidence for eccentricity for some of these events, our analyses do not favor the incorporation of eccentricity compared to the quasi-circular case. While lacking the eccentric evidence of other analyses, we find our analyses marginally shifts the posterior in multiple parameters for several events when allowing eccentricity to be nonzero.

Skynet Astromancer Suite: Gravitymancer

The Gravitymancer processing tool within Skynet’s Astromancer suite opens a unique window for students of introductory astronomy courses to explore the most powerful events observed in our Universe – the merger of binary neutron-star systems and black-hole systems. These merger events produce short-lived bursts of gravitational radiation, as observed by one or more of the following gravitational-wave observatories: LIGO, Virgo, and KAGRA. Students can use Gravitymancer to load and interpret the archival event data, finding useful properties like the total mass and mass ratio of the binary system, distance, and inclination angle. While on the surface, students can interpret gravitational-wave events with an easy-to-use GUI, we present here the complex processing utilized to make this tool work.

Tidal heating as a discriminator for horizons in equatorial eccentric extreme mass ratio inspirals

Tidal heating in a binary black hole system is driven by the absorption of energy and angular momentum by the black hole’s horizon. Previous works have shown that this phenomenon becomes particularly significant during the late stages of an extreme mass ratio inspiral (EMRI) into a rapidly spinning massive black hole, a key focus for future low-frequency gravitational-wave observations by (for instance) the Laser Interferometer Space Antenna mission. Past analyses have largely focused on quasicircular inspiral geometry, with some of the most detailed studies looking at equatorial cases. Though useful for illustrating the physical principles, this limit is not very realistic astrophysically, since the population of EMRI events is expected to arise from compact objects scattered onto relativistic orbits in galactic centers through many-body events. In this work, we extend those results by studying the importance of tidal heating in equatorial EMRIs with generic eccentricities. Our results suggest that accurate modeling of tidal heating is crucial to prevent significant dephasing and systematic errors in EMRI parameter estimation. We examine a phenomenological model for EMRIs around exotic compact objects by parametrizing deviations from the black hole (BH) picture in terms of the fraction of radiation absorbed compared to the BH case. Based on a mismatch calculation, we find that reflectivities as small as |R|2∼O(10−5) are distinguishable from the BH case, irrespective of the value of the eccentricity. We stress, however, that this finding should be corroborated by future parameter estimation studies. Published by the American Physical Society 2024

Cramér-Rao lower bounds on parameter estimation for a circular binary of supermassive black holes in gravitational wave observations using pulsar timing array

Abstract Pulsar timing arrays (PTAs) are effective in detecting low-frequency gravitational waves (GWs), especially in circular binary systems of supermassive black holes. To evaluate the effectiveness and accuracy of PTAs in searching for GW parameter estimation, we use the Cramer-Rao lower bound to estimate the parameters of the Virgo source under various search conditions, including both evolving and non-evolving scenarios, as well as Earth and pulsar term searches, and only Earth term searches. The results show that the estimation accuracy of the inclination angle and GW strain is lower in the evolving condition than in the non-evolving condition because the two parameters participate in the evolving process. In addition, we find that the parameters estimable relates to signal-to-noise ratio, which is beneficial for reducing the dimensionality in the search process. In summary, our method serves as a reference for exploring lower parameter limits under different conditions and assists in assessing the optimization of parameter estimation in GW detection algorithms. This helps lay the theoretical foundation for advances in the field of GWs and the optimization of PTAs.

Inferring the spin distribution of binary black holes using deep learning

The spin characteristics of black holes offer valuable insights into the evolutionary pathways of their progenitor stars. This is crucial for understanding the broader population properties of black holes. Traditional hierarchical Bayesian inference techniques employed to discern these properties often demand substantial time, and consensus regarding the spin distribution of binary black hole (BBH) systems remains elusive. In this study, leveraging observations from GWTC-3, we adopted a machine learning approach to infer the spin distribution of black holes within BBH systems. Specifically, we developed a deep neural network (DNN) and trained it using data generated from a Beta distribution. Our training strategy, involving the segregation of data into 10 bins, not only expedites model training but also enhances the versatility and adaptability of the DNN to accommodate the growing volume of gravitational wave observations. Utilizing Monte Carlo-bootstrap (MC-bootstrap) to generate observation-simulated samples, we derived spin distribution parameters: for the larger BH sample and for the smaller BH sample. Within our constraints, the distributions of component spin magnitudes suggest the likelihood of both black holes in the BBH merger possessing non-zero spin.

RisingTides: An Analytic Modeling Code of Tidal Effects in Binary Neutron Star Mergers

Gravitational waves produced by binary neutron star mergers offer a unique window into matter behavior under extreme conditions. In this context, we analytically model the effect of matter on gravitational waves from binary neutron star mergers. We start with a binary black hole system, leveraging the post-Newtonian formalism for the inspiral and the Backwards-one-Body model for the merger. We combine the two methods to generate a baseline waveform and we validate our results against numerical relativity simulations. Next, we integrate tidal effects in phase and amplitude to account for matter and spacetime interaction using the NRTidal model and test its accuracy against numerical relativity predictions for two equations of state, finding a mismatch around the merger. Subsequently, we lift the restriction on the coefficients to be independent of the tidal deformability and recalibrate them using the numerical relativity predictions. We obtain better fits for phase and amplitude around the merger and are able to extend the phase modeling beyond the merger. We implement our method in new open-source, user-friendly Python code, steered by a Jupyter Notebook, named RisingTides. Our research offers new perspectives on analytically modeling the effect of tides on the gravitational waves from binary neutron star mergers.

Research on Binary Black Hole Systems by Analysis of Gravitational Waves

The mass ratio, effective spin, and chirp mass are three important properties to describe the binary systems of black holes. The gravitational wave sources can be a breakthrough in the investigation of black holes. The formation of black holes is a significant problem to solve as the electromagnetic waves (light) cannot escape from the black hole, and the gravitational waves can be emitted when the binary systems of black holes or neutron stars merge. Based on the detection of gravitational waves, the process of the formation of black holes can be traced and studied in the binary black holes and primordial black holes formed in the early universe. The mass ratio distribution is plotted to investigate the difference between the binary black hole and neutron star black hole and the mass ratio which makes it easier for the merger of the black holes to happen. The investigation of the effective spin helps classify the model of the formation of black holes as there are five models of the black hole. The statistical model can be tested with the chosen data, and the cumulative standard Gaussian distribution is used in this paper. The result states that the model is not suitable for the chosen data and another statistical model should be introduced to analyse the effective spin. These parameters are all important for determining the stage and formation process of the binary systems.

Mass transfer and boson cloud depletion in a binary black hole system

Mass transfer and boson cloud depletion in a binary black hole system

Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243.

The recently reported observation of VFTS 243 is the first example of a massive black-hole binary system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M_{⊙}) and near-circular orbit (e≈0.02) of VFTS 243 suggest that the progenitor star experienced complete collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence level, the natal kick velocity (mass decrement) is ≲10 km/s (≲1.0M_{⊙}), with a full probability distribution that peaks when ≈0.3M_{⊙} were ejected, presumably in neutrinos, and the black hole experienced a natal kick of 4 km/s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0-0.2%. Such a small neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.