Gravitational Waves Research Articles

Mass Transfer in Eccentric Black Hole–Neutron Star Mergers

Abstract Black hole–neutron star binaries are of interest in many ways: they are intrinsically transient, radiate gravitational waves detectable by LIGO, and may produce γ-ray bursts. Although it has long been assumed that their late-stage orbital evolution is driven entirely by gravitational wave emission, we show here that in certain circumstances, mass transfer from the neutron star onto the black hole can both alter the binary's orbital evolution and significantly reduce the neutron star's mass: when the fraction of its mass transferred per orbit is ≳10−2, the neutron star's mass diminishes by order unity, leading to mergers in which the neutron star mass is exceptionally small. The mass transfer creates a gas disk around the black hole before merger that can be comparable in mass to the debris remaining after merger, i.e., ~0.1 M ⊙. These processes are most important when the initial neutron star–black hole mass ratio q is in the range ≈0.2–0.8, the orbital semimajor axis is 40 ≲ a 0/r g ≲ 300 (r g ≡ GM BH/c 2), and the eccentricity is large at e 0 ≳ 0.8. Systems of this sort may be generated through the dynamical evolution of a triple system, as well as by other means.

Low-noise laser intensity noise evaluation system at Hz frequency band for ground-based gravitational wave detection

The direct detection of gravitational waves has opened a new window for understanding the universe and trailblazed multi-messenger astronomy. The frequency band of gravitational waves generated by various astronomical events can cover broadband range, and it is various for detection mechanism and scheme of gravitational waves in different frequency band. For example, The ground-based gravitational wave detection has the frequency band for 10 Hz to 10 kHz to mainly detect which based on Michelson interferometer; The space gravitational wave detection has the frequency band of 0.1 mHz to 1 Hz to mainly detect which based on space interferometer; The pulsar gravitational wave detection has the frequency band for 1×10<sup>-9</sup> Hz to 1×10<sup>-7</sup>Hz to mainly detect which based on pulsar timing array. The next generation ground-based gravitational wave project demands higher sensitivity to detect faint signals, necessitating an assessment system with minimal background noise to accurately measure the laser relative intensity noise. At present, the detection frequency band of ground-based gravitational wave detection devices in operation is mainly concentrated in the range of 10 Hz - 10 kHz. To satisfying the detection sensitivity requirements, the laser relative intensity noise should be accurately evaluated and suppressed to ≤2.0×10<sup>-9</sup>Hz<sup>-1/2</sup>@10 Hz and ≤4.0×10<sup>-7</sup>Hz<sup>-1/2</sup>@10 kHz by photoelectric feedback. This paper constructed an evaluation and characterization system for ground-based gravitational wave band laser intensity noise which based on low noise and high sensitivity photoelectric detection device and combined with LabVIEW and MATLAB algorithm programming for instrument control and data processing. This low noise evaluation system is used to test the background noise of FFT analyzer SR760, preamplifier SR560, photoelectric detector electronics noise and intensity noise of self-developed optical fiber amplifier, and then the data extraction and image processing are carried out by LabVIEW and MATLAB algorithms, and finally the evaluation of ground-based gravitational wave frequency band system is obtained. The experimental results show that the whole electronic noise for the preamplifier SR560 and FFT analyzer SR760 is lower than 3.8×10<sup>-9</sup> Hz<sup>-1/2</sup>@(10 Hz-10 kHz). The electronic noise for the photodetector is lower than 1.4×10<sup>-8</sup>V/√Hz@10 Hz&8.1×10<sup>-9</sup>V/√Hz@10 kHz and the accuracy of the system is calibrated and tested by the standard sinusoidal signal. Finally, the noise of commercial laser is evaluated and compared with the factory data to verify the accuracy of the evaluation system. Related research, device and system development provide hardware, software and theoretical basis for the preparation of high-power low-noise laser light source and gravitational wave detection and provide theoretical basis and evaluation criteria for ground-based gravitational wave detection in China.

Horndeski speed tests with scalar-photon couplings

We revisit multi-messenger constraints from neutron star mergers on the speed of propagation of gravitational and electromagnetic waves in Horndeski and beyond Horndeski theories. By considering non-trivial couplings between the dark energy field and the electromagnetic sector, the electromagnetic wave can propagate through the cosmological background at non-unit speed, altering the phenomenological constraints on its gravitational counterpart. In particular, we show that recent models derived from a Kaluza-Klein compactification of higher dimensional Horndeski models fall into a broader class of theories disformally related to those whose gravitational waves propagate with unit speed. This disformal equivalence can, however, be broken by the gravitational couplings to other sectors with interesting phenomenological consequences. We also consider higher order couplings between the scalar and the photon with second order field equations, and show that they are not compatible with constraints coming from multi-messenger speed tests and the decay of the gravitational wave.

Gravitational-wave signatures of gravito-electromagnetic couplings

Gravitational waves (GWs) can undoubtedly serve as a messenger from the early Universe acting as well as a novel probe of the underlying gravity theory. In this work, motivated by one-loop vacuum-polarization effects on curved spacetime, we investigate a gravitational theory with non-minimal curvature-electromagnetic coupling terms of the form ξR/M Pl2 F μν F μν , where M Pl is the reduced Planck mass, R is the scalar curvature and F μν the Faraday tensor, being responsible for the generation of primordial electromagnetic fields. We study then the GW signatures of such coupling terms deriving in particular for the first time to the best of our knowledge the modified tensor modes equation of motion. Remarkably, we find a universal infrared (IR) frequency scaling f 5 of the electromagnetically induced GW (EMIGW) signal, which, depending on the energy scale of inflation, the duration of inflation and reheating as well as the dynamical behaviour of the coupling function ξ, can be well within the detection sensitivity bands of GW experiments such as SKA, LISA, ET and BBO, being thus potentially detectable in the future by GW observatories.

Observing kinematic anisotropies of the stochastic background with LISA

We propose a diagnostic tool for future analyses of stochastic gravitational wave background signals of extra-galactic origin in LISA data. Next-generation gravitational wave detectors hold the capability to track unresolved gravitational waves bundled into a stochastic background. This composite background contains cosmological and astrophysical contributions, the exploration of which offers promising avenues for groundbreaking new insights into very early universe cosmology as well as late-time structure formation. In this article, we develop a full end-to-end pipeline for the extraction of extra-galactic signals, based on kinematic anisotropies arising from the galactic motion, via full-time-domain simulations of LISA's response to the gravitational wave anisotropic sky. Employing a Markov-Chain-Monte-Carlo map-making scheme, multipoles up to ℓ=2 are recovered for scale-free spectra in the case of a high signal-to-noise ratio. We demonstrate that our analysis is consistently beating sample variance and is robust against statistical and systematic errors. The impact of instrumental noise on the extraction of kinematic anisotropies is investigated, and we establish a detection threshold of Ω GW ≳ 5 × 10-8 in the presence of instrument-induced noise. Potential avenues for improvement in our methodology are highlighted.

Gravitational waves induced by scalar perturbations with a broken power-law peak

We give an analytical approximation for the energy spectrum of the scalar-induced gravitational waves (SIGWs) generated by a broken power-law power spectrum, and find that both the asymptotic power-law tails and the intermediate peak contribute distinct features to the SIGW spectrum. Moreover, the broken power-law power spectrum has abundant near-peak features and our results can be used as a near-peak approximation that covers a wide range of models. Our analytical approximation is useful in the rapid generation of the SIGW energy spectrum, which is beneficial for gravitational wave data analysis.

Gravitational-wave Dark Siren Cosmology Systematics from Galaxy Weighting

The detection of GW170817 and the measurement of its redshift from the associated electromagnetic counterpart provided the first gravitational-wave (GW) determination of the Hubble constant (H 0), demonstrating the potential power of standard siren cosmology. In contrast to this “bright siren” approach, the “dark siren” approach can be utilized for GW sources in the absence of an electromagnetic counterpart: One considers all galaxies contained within the localization volume as potential hosts. When statistically averaging over the potential host galaxies, weighting them by physically motivated properties (e.g., tracing star formation or stellar mass) could improve convergence. Using mock galaxy catalogs, we explore the impact of these weightings on the measurement of H 0. We find that incorrect weighting schemes can lead to significant biases due to two effects: the assumption of an incorrect galaxy redshift distribution, and preferentially weighting incorrect host galaxies during the inference. The magnitudes of these biases are influenced by the number of galaxies along each line of sight, the measurement uncertainty in the GW luminosity distance, and correlations in the parameter space of galaxies. We show that the bias may be overcome from improved localization constraints in future GW detectors, a strategic choice of priors or weighting prescription, and by restricting the analysis to a subset of high-signal-to-noise ratio events. We propose the use of hierarchical inference as a diagnostic of incorrectly weighted prescriptions. Such approaches can simultaneously infer the correct weighting scheme and the values of the cosmological parameters, thereby mitigating the bias in dark siren cosmology due to incorrect host-galaxy weighting.

Dual gravitational wave signatures of instant preheating

In the instant preheating scenario efficient particle production occurs immediately following the period of inflationary expansion in the early Universe. We demonstrate that instant preheating predicts unique gravitational wave (GW) signals arising from two distinct origins. One source is the bremsstrahlung GWs produced through the decay of superheavy particles, an inevitable consequence of instant preheating. The other is GWs generated from the nonlinear dynamics of the inflaton and coupled scalar fields. Using numerical simulations, we show that the peak of the GW spectrum shifts depending on the coupling constants of the theory. The detection of these dual GW signatures, characteristic of instant preheating, provides novel opportunities for probing the dynamics of the early Universe.

Periodic orbits and their gravitational wave radiations around the Schwarzschild-MOG black hole

Periodic orbits and their gravitational wave radiations around the Schwarzschild-MOG black hole

Primordial black holes in SB SUSY Gauss-Bonnet inflation

Here, we explore the formation of primordial black holes (PBHs) within a scalar field inflationary model coupled to the Gauss-Bonnet (GB) term, incorporating the low-scale spontaneously broken supersymmetric (SB SUSY) potential.The coupling function amplifies the curvature perturbations, consequently leading to the formation of PBHs and detectable secondary gravitational waves (GWs).Through the adjustment of the model parameters, the inflaton can be decelerated during an ultra-slow-roll (USR) phase, thereby augmenting curvature perturbations. Beside the observational constraints, the swampland criteria are investigated.Our computations forecast the formation of PBHs with masses around 𝒪(10)M ⊙, aligning with the observational data of LIGO-Virgo, and PBHs with masses 𝒪(10-6)M ⊙ as potential explanation for the ultrashort-timescale microlensing events recorded in the OGLE data.Additionally, our proposed mechanism can generate PBHs with masses around 𝒪(10-13)M ⊙, constituting roughly 99% of the dark matter.The density parameters of the produced GWs (ΩGW 0) intersect with the sensitivity curves of GW detectors. Two cases of our model fall within the nano-Hz frequency regime. One of them satisfies the power-law scaling as ΩGW(f) ∼ f 5-γ, with the γ = 3.51, which is consistent with the data of NANOGrav 15-year.

Recovering Pulsar Periodicity from Time-of-arrival Data by Finding the Shortest Vector in a Lattice

The strict periodicity of pulsars is one of the primary ways through which their nature and environment can be studied, and it has also enabled precision tests of general relativity and studies of nanohertz gravitational waves using pulsar timing arrays (PTAs). Identifying such a periodicity from a discrete set of arrival times is a difficult algorithmic problem, In particular when the pulsar is in a binary system. This challenge is especially acute in γ-ray pulsar astronomy, as there are hundreds of unassociated Fermi-LAT sources that may be produced by γ-ray emission from unknown pulsars. Recovering their timing solutions will help reveal their properties and may allow them to be added to PTAs. The same issue arises when attempting to recover a strict periodicity for repeating fast radio bursts (FRBs). Such a detection would be a major breakthrough, providing us with the FRB source’s age, magnetic field, and binary orbit. The problem of recovering a timing solution from sparse time-of-arrival data is currently unsolvable for pulsars in unknown binary systems, and incredibly hard even for isolated pulsars. In this paper, we frame the timing recovery problem as the problem of finding a short vector in a lattice and obtain the solution using off-the-shelf lattice reduction and sieving techniques. As a proof of concept, we solve PSR J0318+0253, a millisecond γ-ray pulsar discovered by FAST in a γ-ray-directed search, in a few CPU minutes. We discuss the assumptions of the standard lattice techniques and quantify their performance and limitations.

Preheating and gravitational waves production in hybrid metric-Palatini model

Preheating and gravitational waves production in hybrid metric-Palatini model

Criteria for identifying and evaluating locations that could potentially host the Cosmic Explorer observatories.

Cosmic Explorer is a next-generation ground-based gravitational-wave observatory that is being designed in the 2020s and is envisioned to begin operations in the 2030s together with the Einstein Telescope in Europe. The Cosmic Explorer concept currently consists of two widely separated L-shaped observatories in the United States, one with 40 km-long arms and the other with 20 km-long arms. This order of magnitude increase in scale with respect to the LIGO-Virgo-KAGRA observatories will, together with technological improvements, deliver an order of magnitude greater astronomical reach, allowing access to gravitational waves from remnants of the first stars and opening a wide discovery aperture to the novel and unknown. In addition to pushing the reach of gravitational-wave astronomy, Cosmic Explorer endeavors to approach the lifecycle of large scientific facilities in a way that prioritizes mutually beneficial relationships with local and Indigenous communities. This article describes the (scientific, cost and access, and social) criteria that will be used to identify and evaluate locations that could potentially host the Cosmic Explorer observatories.

Comparison of the Origin of Short Gamma-Ray Bursts with or without Extended Emission

The merger of compact binary stars produces short gamma-ray bursts (sGRBs), involving channels such as neutron star–neutron star (BNS) and neutron star–black hole (NS–BH). The association between sGRB 170817A and gravitational wave GW170817 provides reliable evidence for the BNS channel. Some speculations suggest that sGRBs with extended emission (EE) may represent another distinct population. The offset is the distance between the GRB sky localization and the host galaxy center. We compared the offset distributions of these two types of samples (46 sGRBs with EE and 9 without EE samples) and found that they follow the same distribution. Utilizing nonparametric methods, we examined the luminosity function and formation rate of sGRBs without any assumptions. The luminosity function can be described as ψ(L0)∝L0−0.12±0.01 for L0<L0b ( ψ(L0)∝L0−0.73±0.02 and for L0>L0b ) for sGRBs without EE and ψ(L0)∝L0−0.13±0.003 for L0<L0b ( ψ(L0)∝L0−0.61±0.01 and for L0>L0b ) for sGRBs with EE. The formation rate is characterized as ρ(z) ∝ (1 + z)−3.04±0.10 for z < 1 and as ρ(z) ∝ (1 + z)−0.29±0.38 for 1 < z < 3 for sGRBs without EE, while for sGRBs with EE, it is ρ(z) ∝ (1 + z)−3.85±0.15 for z < 1 and ρ(z) ∝ (1 + z)−0.40±1.11 for 1 < z < 3. Our findings suggest no significant difference in the progenitors of sGRBs with and without EE when considered in terms of spatial offsets, formation rates, and luminosity function.

Merging Black Holes: Insights from Gravitational Wave Observations

Before the first formal and direct detection of gravitational waves happened in 2015 by LIGO, Einstein had already predicted its presence in 1916 through his theory of general relativity. These gravitational waves are produced in cosmic events such as colliding and merging black holes, which means that their detection and investigation can be used to study the characteristics and properties of Black Hole Mergers. Studying black hole mergers can enable us to gain a deeper understanding of the universe’s cosmic history and structure. This paper provides a brief summary on the insights of Black Hole mergers from Gravitational Wave Observations, while also exploring some of the observational technique used, such as the technique of interferometry and Pulsar Timing arrays.

Implications of cosmologically coupled black holes for pulsar timing arrays

It has been argued that realistic models of (singularity-free) black holes (BHs) embedded within an expanding Universe are coupled to the large-scale cosmological dynamics, with striking consequences, including pure cosmological growth of BH masses. In this pilot study, we examine the consequences of this growth for the stochastic gravitational wave background (SGWB) produced by inspiraling supermassive cosmologically coupled BHs. We show that the predicted SGWB amplitude is enhanced relative to the standard uncoupled case, while maintaining the frequency scaling of the spectral energy density. For the case where BH masses grow with scale factor as , thus contributing as a dark energy component to the cosmological dynamics, can be enhanced by more than an order of magnitude. This has important consequences for the SGWB signal detected by pulsar timing arrays, whose measured amplitude is slightly larger than most theoretical predictions for the spectrum from inspiraling binary BHs, a discrepancy which can be alleviated by the cosmological mass growth mechanism.

Limiting Rotation Rate of Neutron Stars from Crust Breaking and Gravitational Waves

Limiting Rotation Rate of Neutron Stars from Crust Breaking and Gravitational Waves

Charting the nanohertz gravitational wave sky with pulsar timing arrays

Charting the nanohertz gravitational wave sky with pulsar timing arrays

Constraining the Binarity of Massive Black Holes in the Galactic Center and Some Nearby Galaxies via Pulsar Timing Array Observations of Gravitational Waves

Massive black holes (MBHs) exist in the Galactic center (GC) and other nearby galactic nuclei. As a natural outcome of galaxy mergers, some MBHs may have a black hole (BH) companion. In this paper, assuming that the MBHs in the GC and some nearby galaxies are in binaries with orbital periods ranging from months to years (gravitational-wave frequency ∼1–100 nHz), we investigate the detectability of gravitational waves from these binary MBHs (BBHs) and constraints on the parameter space for the existence of BBHs in the GC, Large Magellanic Cloud (LMC), M31, M32, and M87 that may be obtained by current/future pulsar timing array (PTA) observations. We find that a BBH in the GC, if any, can be revealed by the Square Kilometre Array PTA (SKA-PTA) if it has mass ratio q ≳ 10−4–10−3 and semimajor axis a ∼ 20–103 au. The existence of a BH companion of the MBH can be revealed by SKA-PTA with ∼20 yr observations in M31 if q ≳ 10−4 and a ∼ 102–104 au or in M87 if q ≳ 10−5 and a ∼ 103–2 × 104 au, but not in the LMC and M32 if q ≪ 1. If a number of millisecond stable pulsars with distances ≲0.1–1 pc away from the central MBH in the GC, the LMC, M32, or M31 can be detected in future and applied to PTAs, a BH companion with mass even down to ∼100 M ⊙, close to stellar masses, can be revealed by such PTAs. Future PTAs are expected to provide an independent way to reveal BBHs and low-mass MBH companions in the GC and nearby galaxies, improving our understandings of the formation and evolution of MBHs and galaxies.

Gravitational and electromagnetic Cherenkov radiation constraints in modified dispersion relations

Gravitational and electromagnetic Cherenkov radiation constraints in modified dispersion relations