Search

The Milky Way galaxy is estimated to host up to a billion stellar-mass solitary black holes (BHs). The number and distribution of BH masses can provide crucial information about the processes involved in BH formation, the existence of primordial BHs, and the interpretation of gravitational wave (GW) signals detected in LIGO–VIRGO–KAGRA. Sahu et al. recently confirmed one solitary stellar-mass BH in our galaxy using astrometric microlensing. This work proposes a novel mechanism to identify such BH by analysing the frequency and damping of the quasi-normal modes of GW generated from the interaction of the BH and EM wave originating from a transient electromagnetic (TEM) source. The incoming EM waves distort the curvature of a BH, releasing GWs as it returns to a steady state. Using the covariant semitetrad formalism, we quantify the generated GWs via the Regge – Wheeler tensor and relate the GW amplitude to the energy of the TEM. We demonstrate that isolated BHs at a distance of 50 pc from Earth can be detected by LIGO A+ and 100 pc by Cosmic Explorer/Einstein Telescope. Additionally, we discuss the observational implications for orphan afterglows associated with GRBs, highlighting the potential for further discoveries. [ABSTRACT FROM AUTHOR]

We present recent advancements in the Japanese space-based gravitational-wave detectors DECIGO (Deci-Hertz Gravitational-wave Observatory) and B-DECIGO, focusing on refined sensitivity estimation, binary black hole localization with B-DECIGO and DECIGO’s capability to measure the early universe’s reheating temperature. Through simulations and experiments involving back-linked interferometers, pre-stabilized lasers and optimized satellite orbits, we demonstrate key techniques that improve signal-to-noise ratios across a broad frequency range. Our work incorporates advanced parameter adjustments, including mirror geometry optimization and noise reduction techniques such as square completion and optical springs, leading to enhanced signal-to-noise ratios over a wide frequency range. These developments pave the way for B-DECIGO and DECIGO to explore high-redshift cosmology and early universe phenomena. [ABSTRACT FROM AUTHOR]

Next-generation gravitational-wave detectors, with their improved sensitivity and wider frequency bandwidth, will be capable of observing almost every compact binary coalescence signal from epochs before the first stars began to form, increasing the number of detectable binaries to hundreds of thousands annually. This will enable us to observe compact objects through cosmic time, probe extreme matter phenomena, do precision cosmology, study gravity in strong field dynamical regimes and potentially allow observation of fundamental physics beyond the standard model. However, the richer data sets produced by these detectors will pose new computational, physical and astrophysical challenges, necessitating the development of novel algorithms and data analysis strategies. To aid in these efforts, this paper introduces gwforge, a user-friendly, lightweight Python package, to generate mock data for next-generation detectors. gwforge allows users to seamlessly simulate data while abstracting away technical complexities, enabling more efficient testing and development of analysis pipelines. Additionally, the package's data generation process is optimized using high-throughput systems like HTCondor, significantly speeding up the simulation of large populations of gravitational-wave events. We demonstrate the package's capabilities through data simulation examples and highlight a few potential applications: performance loss due to foreground noise, bright-siren cosmology and impact of waveform systematics on binary parameter estimation. [ABSTRACT FROM AUTHOR]

Mature neutron stars are expected to exhibit gravity g modes due to stratification caused by a varying matter composition in the high-density core. By employing the BSk equation-of-state family, and working within the relativistic Cowling approximation, we examine how subtle differences in the nuclear matter assumptions impact on the g-mode spectrum. We investigate the possibility of detecting individual g-mode resonances during a binary inspiral with current and next-generation ground-based detectors, like Cosmic Explorer and the Einstein Telescope. Our results suggest that these resonances may be within the reach of future detectors, especially for low-mass stars with |$M\lesssim 1.4\,\mathrm{ M}_\odot$|⁠. [ABSTRACT FROM AUTHOR]

We present the design and commissioning of a cryogenic low-vibration test facility that measures displacement noise from a gram-scale silicon cantilever at the level of 10 − 16 m / H z at 1 kHz. This sensitivity is necessary for future tests of thermal noise models on cross sections of silicon suspension samples proposed for future gravitational-wave detectors. A volume of ∼36 l is enclosed by radiation shields cooling an optical test cavity that is suspended from a multi-stage pendulum chain providing isolation from acoustic and environmental noise. This 3 kg test cavity housing a crystalline silicon cantilever is radiatively cooled to 123 K in 41 h and held at that temperature over many months with a relative temperature stability of ±1 mK. The facility housing the test cavity is sensitive to cavity length changes, which can resolve thermal fluctuations at the desired sensitivity. It is capable of interferometrically measuring temperature-dependent broadband displacement noise directly between 50 Hz and 10 kHz, where current and future ground-based gravitational wave observatories are the most sensitive. With a suitable cantilever design, the cryogenic facility we describe here will allow for the measurement of broadband thermal noise in crystalline silicon at 123 K. This will guide the design of suspensions in planned future cryogenic ground-based gravitational-wave detectors such as LIGO Voyager and may have implications for suspensions in the Einstein Telescope. This facility is also suitable for the testing of new mirror coatings at cryogenic temperatures. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Gravitational waves (GWs) from primordial black holes (PBHs) inspiraling within neutron stars (NSs)—should they exist—are detectable by ground-based detectors and offer a unique insight into the internal structure of NSs. To provide accurate templates for GW searches, we solve Einstein's equations within NSs and calculate the orbital motion of the captured PBH by considering dynamical friction, accretion, and gravitational radiation. Equipped with precise GW waveforms for PBHs inspiraling inside NSs, we find that the Einstein Telescope can differentiate between various equations of state for NSs. As PBHs inspiral deeper into NSs, the GW frequency rises near the surface, then decreases to a constant value deeper within NSs. The distinctive characteristics of GW frequency serve as the smoking gun for GW signals emitted by PBHs inspiraling inside NSs and can be used to probe the nuclear matter in the crust and core of NSs. [ABSTRACT FROM AUTHOR]

In space gravitational wave detection missions, the gravity and its gradients produced by the spacecraft on the two Test Masses (TMs) are commonly referred to as the Self-Gravity(SG). It is an important source of TM disturbances in gravitational wave detection and other drag-free space missions and will affect the TM acceleration noise in many ways. The SG can be reduced by adding Balance Masses (BMs). But for typical space gravitational wave detectors, in which the sensitive axes of the two TMs are at an angle of 60 ° , the couplings of different SG components of two TMs make the gravity compensation process complicated in practice, which is normally an iterative process. This paper analyses the correspondence between the SG components of the two TMs and the spherical harmonics of different orders, and proposes a compensation method based on spherical multipole expansion. This method allows independent design of the BMs for most of the main SG components, without couplings and iterations. To verify this method, a self-gravity compensation simulation is carried out by using a demonstrating spacecraft structural model for TianQin gravitational wave detection mission. Three sets of BMs are designed on the outer surface of the inertial sensor vacuum chamber, to compensate for the two linear accelerations and one linear gradient that exceed the requirements. The results show that the SG components after compensation are two orders of magnitude lower than the initial level, and all the components meet the preliminary requirements of TianQin mission. This study could provide reference for the engineering design and development of the spacecraft and inertial sensor payload for space gravitational wave detection missions. • The correspondence of self-gravity and spherical harmonics is analyzed and decoupled. • A set of azimuth for balance masses are provided for each self-gravity components. • A high efficiency non-iterative self-gravity compensation method and flow is proposed. • Calculation and compensation flow are tested using a demonstrating spacecraft model. • The self-gravity after compensation satisfies the requirements of TianQin mission. [ABSTRACT FROM AUTHOR]

Gravitational-wave observations by the laser interferometer gravitational-wave observatory (LIGO) and Virgo have provided us a new tool to explore the Universe on all scales from nuclear physics to the cosmos and have the massive potential to further impact fundamental physics, astrophysics, and cosmology for decades to come. In this paper we have studied the science capabilities of a network of LIGO detectors when they reach their best possible sensitivity, called A ♯ , given the infrastructure in which they exist and a new generation of observatories that are factor of 10 to 100 times more sensitive (depending on the frequency), in particular a pair of L-shaped cosmic explorer (CE) observatories (one 40 km and one 20 km arm length) in the US and the triangular Einstein telescope with 10 km arms in Europe. We use a set of science metrics derived from the top priorities of several funding agencies to characterize the science capabilities of different networks. The presence of one or two A ♯ observatories in a network containing two or one next generation observatories, respectively, will provide good localization capabilities for facilitating multimessenger astronomy (MMA) and precision measurement of the Hubble parameter. Two CE observatories are indispensable for achieving precise localization of binary neutron star events, facilitating detection of electromagnetic counterparts and transforming MMA. Their combined operation is even more important in the detection and localization of high-redshift sources, such as binary neutron stars, beyond the star-formation peak, and primordial black hole mergers, which may occur roughly 100 million years after the Big Bang. The addition of the Einstein Telescope to a network of two CE observatories is critical for accomplishing all the identified science metrics including the nuclear equation of state, cosmological parameters, the growth of black holes through cosmic history, but also make new discoveries such as the presence of dark matter within or around neutron stars and black holes, continuous gravitational waves from rotating neutron stars, transient signals from supernovae, and the production of stellar-mass black holes in the early Universe. For most metrics the triple network of next generation terrestrial observatories are a factor 100 better than what can be accomplished by a network of three A ♯ observatories. [ABSTRACT FROM AUTHOR]

The strong gravitational potential of neutron stars (NSs) makes them ideal astrophysical objects for testing extreme gravity phenomena. We explore the potential of NS X-ray pulsed light curve observations to probe deviations from general relativity (GR) within the scalar–tensor theory (STT) of gravity framework. We compute the flux from a single, circular, finite-size hot spot, accounting for light bending, Shapiro time delay, and Doppler effect. We focus on the high-compactness regime, i.e., close to the critical GR value G M / (c 2 R) = 0.284 , over which multiple images of the spot appear and impact crucially the light curves. Our investigation is motivated by the increased sensitivity of the pulse to the scalar charge of the spacetime in such high compactness regimes, making these systems exceptionally suitable for scrutinizing deviations from GR, notably phenomena such as spontaneous scalarization, as predicted by STT. We find significant differences in NS observables, e.g., the flux of a single spot can differ up to 80% with respect to GR. Additionally, reasonable choices for the STT parameters that satisfy astrophysical constraints lead to changes in the NS radius relative to GR of up to approximately 10%. Consequently, scalar parameters might be better constrained when uncertainties in NS radii decrease, where this could occur with the advent of next-generation gravitational wave detectors, such as the Einstein Telescope and LISA, as well as future electromagnetic missions like eXTP and ATHENA. Thus, our findings suggest that accurate X-ray data of the NS surface emission, jointly with refined theoretical models, could constrain STTs. [ABSTRACT FROM AUTHOR]

This "vision document" is about what the future has in store for tests of general relativity with gravitational wave detectors. I will make an honest attempt to answer this question by addressing the role of inspiral-based and ringdown-based tests; recent progress on quasinormal modes in modified theories of gravity; the complementarity between light ring tests and ringdown tests; and the interesting possibility of observing some of the nonlinear effects predicted by general relativity. I may well prove to be wrong. To quote Yogi Berra: "It's hard to make predictions, especially about the future". [ABSTRACT FROM AUTHOR]

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The toolbox to study the Universe grew on 14 September 2015 when the LIGO–Virgo collaboration heard a signal from two colliding black holes between 30 and 250 Hz. Since then, many more gravitational waves have been detected as detectors continue to increase sensitivity. However, the current and future interferometric detectors will never be able to detect gravitational waves below a few Hz due to oceanic activity on Earth. An interferometric space mission, the laser interferometer space antenna, will operate between 1 mHz and 0.1 Hz, leaving a gap in the decihertz band. To detect gravitational-wave signals also between 0.1 and 1 Hz, the Lunar Gravitational-wave Antenna will use an array of seismic stations. The seismic array will be deployed in a permanently shadowed crater on the lunar south pole, which provides stable ambient temperatures below 40 K. A cryogenic superconducting inertial sensor is under development that aims for fm/ √ Hz sensitivity or better down to several hundred mHz, and thermal noise limited below that value. Given the 10 6 m size of the Moon, strain sensitivities below 10 − 20 1/ √ Hz can be achieved. The additional cooling is proposed depending on the used superconductor technology. The inertial sensors in the seismic stations aim to make a differential measurement between the elastic response of the Moon and the inertial sensor proof-mass motion induced by gravitational waves. Here, we describe the current state of research toward the inertial sensor, its applications, and additional auxiliary technologies in the payload of the lunar gravitational-wave detection mission. [ABSTRACT FROM AUTHOR]

We present a new constraint on the Hubble constant (⁠|$H_0$|⁠) from the standard dark siren method using a sample of five well-covered gravitational wave (GW) alerts reported during the first part of the fourth observing run of the Laser Interferometer Gravitational-Wave Observatory (LIGO), the Virgo and Kamioka Gravitational Wave Detector (KAGRA) collaborations (LVK) and with three updated standard dark sirens from third observation run in combination with the previous constraints from the first three runs. Our methodology relies on the galaxy catalogue method alone. We use a deep learning method to derive the full probability density estimation of photometric redshifts using the Legacy Survey catalogues. We add the constraints from well localized binary black hole mergers to the sample of standard dark sirens analysed in our previous work. We combine the |$H_0$| posterior for 5 new standard sirens with other 10 previous events (using the most recent available data for the five novel events and updated three previous posteriors from O3), finding |$H_0 = 70.4^{+13.6}_{-11.7}~{\rm km~s^{-1}~Mpc^{-1}}$| (68 per cent confidence interval) with the catalogue method only. This result represents an improvement of |$\sim 23~{{\ \rm per\ cent}}$| comparing the new 15 dark siren constraints with the previous 10 dark siren constraints and a reduction in uncertainty of |$\sim 40~{{\ \rm per\ cent}}$| from the combination of 15 dark and bright sirens compared with the GW170817 bright siren alone. The combination of dark and bright siren GW170817 with recent jet constraints yields |$H_0$| of |$68.0^{+4.4}_{-3.8}~{\rm km~s^{-1}~Mpc^{-1}}$|⁠ , a |$\sim 6~{{\ \rm per\ cent}}$| precision from standard sirens, reducing the previous constraint uncertainty by |$\sim 10~{{\ \rm per\ cent}}$|⁠. [ABSTRACT FROM AUTHOR]

15 ultra-pure sapphire single crystals of 32 mm diameter and 100 mm long were grown under a stationary stable regime using the Czochralski (Cz) technique. Despite varying several growth parameters, the obtained crystals were transparent without visible macroscopic defects such as cracks, inclusions and grain boundaries. The optical absorption coefficients (α) at the 1064 nm wavelength of the grown sapphire crystals were mapped by Photothermal Deflection Spectroscopy (PDS). The crystals grown along c-axis using low pulling rates lower than 1.5 mm h−1, at 1064 nm present an very low optical absorption coefficients (α = 11 ppm cm−1). At such low levels, the origin of the optical absorption has never been explained. However, in this paper we point toward the role of Fe2+–Fe3+ and Ti3+–Ti3+ pairs. These results open the route to upscaling the growth process to achieve ultra-large sapphire crystals with outstanding optical performances, which are a key for the next generation of gravitational wave detectors. [ABSTRACT FROM AUTHOR]

The document is a contents list from the journal CrystEngComm, which focuses on the design and understanding of solid-state and crystalline materials. It includes various papers on topics such as metal-organic frameworks, molecular magnetic materials, and photocatalytic properties. The journal is published by The Royal Society of Chemistry, a leading chemistry community that reinvests profits back into the chemistry community. [Extracted from the article]

Phase-sensitive amplification of squeezed states is a technique to mitigate high detection loss, which is especially attractive at 2 µ m wavelengths. We derived an analytical model proving that amplified squeezed states can mitigate phase noise significantly. Our model discloses two practical parameters: the effective measurable squeezing and the effective detection efficiency of amplified squeezed states. A realistic case study includes the dynamics of the gain-dependent impedance matching conditions of the amplifier. Our results recommend operating the optical parametric amplifier at high gains because of the signal-to-noise ratio's robustness to phase noise. Amplified squeezed states are relevant in proposed gravitational wave detectors and interesting for applications in quantum systems degraded by the output coupling loss in optical waveguides. [ABSTRACT FROM AUTHOR]

Searches for continuous-wave gravitational radiation in data collected by modern long-baseline interferometers, such as the Laser Interferometer Gravitational-wave Observatory (LIGO), the Virgo interferometer, and the Kamioka Gravitational Wave Detector, can be memory intensive. A digitization scheme is described that reduces the 64-bit interferometer output to a one- or two-bit data stream while minimizing distortion and achieving considerable reduction in storage and input/output cost. For the representative example of the coherent, maximum-likelihood matched filter known as the F -statistic, it is found using Monte Carlo simulations that the injected signal only needs to be ≈24% stronger (for one-bit data) and ≈6.4% stronger (for two-bit data with optimal thresholds) than a 64-bit signal in order to be detected with 90% probability in Gaussian noise. The foregoing percentages do not change significantly when the signal frequency decreases secularly, or when the noise statistics are not Gaussian, as verified with LIGO Science Run 6 data. [ABSTRACT FROM AUTHOR]

In this paper, we calculate the energy, signal-to-noise ratio (SNR), detection range, and angular anisotropy of the matter, matter memory, and neutrino memory gravitational-wave (GW) signatures of 21 three-dimensional initially nonrotating core-collapse supernova (CCSN) models carried to late times. We find that inferred energy, SNR, and detection range are angle-dependent quantities, and that the spread of possible energy, signal to noise, and detection ranges across all viewing angles generally increases with progenitor mass. When examining the low-frequency matter memory and neutrino memory components of the signal, we find that the neutrino memory is the most detectable component of a CCSN GW signal, and that DECIGO is best equipped to detect both matter memory and neutrino memory. Moreover, we find that the polarization angle between the h + and h × strains serves as a unique identifier of matter and neutrino memory. Finally, we develop a Galactic density- and stellar mass-weighted formalism to calculate the rate at which we can expect to detect CCSN GW signals with the Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO). When considering only the matter component of the signal, the aLIGO detection rate is around 65% of the total Galactic supernova rate, but increases to 90% when incorporating the neutrino memory component. We find that all future detectors (Einstein Telescope, Cosmic Explorer, DECIGO) will be able to detect CCSN GW signals from the entire Galaxy, and for the higher-mass progenitors even into the Local Group of galaxies. [ABSTRACT FROM AUTHOR]

Laser interferometry plays a crucial role in laser ranging for high-precision space missions such as GRACE (Gravity Recovery and Climate Experiment) Follow-On-like missions and gravitational wave detectors. For such accuracy of modern space missions, a precise relativistic model of light propagation is required. With the post-Newtonian approximation, we utilize the Synge world function method to study the light propagation in the Earth's gravitational field, deriving the gravitational delays up to order c −4. Then, we investigate the influences of gravitational delays in three inter-satellite laser ranging techniques, including one-way ranging, dual one-way ranging, and transponder-based ranging. By combining the parameters of Kepler orbit, the gravitational delays are expanded up to the order of e 2 (e is the orbital eccentricity). Finally, considering the GRACE Follow-On-like missions, we estimate the gravitational delays to the level of picometer. The results demonstrate some high-order gravitational and coupling effects, such as c −4-order gravitational delays and coupling of Shapiro and beat frequency, which may be non-negligible for higher precision laser ranging in the future. [ABSTRACT FROM AUTHOR]

We consider a scenario with axions/axion-like particles Chern–Simons gravity coupling, such that gravitational waves can be produced directly from axion wave parametric resonance in the early universe after inflation. This axion gravity term is less constrained compared to the well-searched axion photon coupling and can provide a direct and efficient production channel for gravitational waves. Such stochastic gravitational waves can be detected by either space/ground-based gravitational wave detectors or pulsar timing arrays for a broad range of axion masses and decay constants. [ABSTRACT FROM AUTHOR]

TianQin (TQ) mission, the sole proposed gravitational wave detection project in geocentric orbit at an altitude of approximately 1 0 5 km, traverses diverse geomagnetic regions. This paper employs a hybrid model to simulate the ambient magnetic field along the TQ orbit, investigating magnetically-induced acceleration noise under varying satellite-sun angles (SSA) and solar activity levels. The highest noise level, approximately 1 0 − 16 ms − 2 Hz − 1 / 2 , occurs during transregional periods between the magnetosheath (MSH) and magnetotail (MTL). Noise within the MSH region is an order of magnitude lower than the former, with the MTL region exhibiting the lowest levels, although geomagnetic storms can equalize noise in both regions. Statistical analysis indicates that noise in the MTL region correlates with SSA and solar wind dynamic pressure, displaying a spectral characteristic of f − 1. 03 ± 0. 075 , while the MSH region shows a Kolmogorov turbulence spectrum near the flank and f − 0. 5 at the subsolar region. [Display omitted] • Efficient and accurate hybrid model for simulating ambient magnetic fields in far-Earth orbit. • Identified peak noise levels during transregional periods between the magnetosheath and magnetotail. • Demonstrated significant influence of solar activity and satellite-sun angles on magnetically-induced noise. • Provided essential insights on noise management for future geocentric gravitational wave detectors. [ABSTRACT FROM AUTHOR]

The development of the Drag-Free and Attitude Control System is crucial for space-based gravitational wave detectors. The Drag-Free and Attitude Control System includes for spacecraft attitude control, drag-free control, moving optical subassemblies pointing control, and test masses electrostatic control during multiple phases of the mission lifetime. An accurate model of the spacecraft dynamics model is not only a precondition for the control design of Drag-Free and Attitude Control System, but also can serve as a valuable reference to assess the noise budget of gravitational wave detectors. This paper presents a generic, nonlinear mathematical model that describes the multi-body dynamics for the gravitational wave detectors. The model fully considers the couplings between the bodies involved, with a particular focus on the impact of the moving optical subassemblies on the spacecraft attitude. Additionally, a corresponding reduced model for the control design of the science mode is divided. Both models are validated numerically by Monte Carlo simulations and motion analysis, respectively. • Introduce a spacecraft dynamics model that fully describes the motion coupling. • Simscape simulation has validated the accuracy of the dynamics model. • The spacecraft dynamics model is applicable to multiple phases of motion. • Monte Carlo simulations have validated the applicability to different parameters. [ABSTRACT FROM AUTHOR]

The gravitational wave (GW) signal from binary black hole (BBH) mergers is a promising probe of Population III (Pop III) stars. To fully unleash the power of the GW probe, one important step is to understand the relative importance and features of different BBH evolution channels. We model two channels, isolated binary stellar evolution (IBSE) and nuclear star cluster-dynamical hardening (NSC-DH), in one theoretical framework based on the semi-analytical code a-sloth , under various assumptions on Pop III initial mass function (IMF), initial binary statistics and high- z nuclear star clusters (NSCs). The NSC-DH channel contributes |$\sim 8\!-\!95{{\ \rm per\ cent}}$| of Pop III BBH mergers across cosmic history, with higher contributions achieved by initially wider binary stars, more top-heavy IMFs, and more abundant high- z NSCs. The dimensionless stochastic GW background (SGWB) produced by Pop III BBH mergers has peak values |$\Omega ^{\rm peak}_{\rm GW}\sim 10^{-11}\!-\!8\times 10^{-11}$| around observer-frame frequencies |$\nu \sim 10\!-\!100\ \rm Hz$|⁠. The Pop III contribution can be a non-negligible (⁠|$\sim 2\!-\!32{{\ \rm per\ cent}}$|⁠) component in the total SGWB at |$\nu \lesssim 10\ \rm Hz$|⁠. The estimated detection rates of Pop III BBH mergers by the Einstein Telescope are |$\sim 6\!-\!230$| and |$\sim 30\!-\!1230\ \rm yr^{-1}$| for the NSC-DH and IBSE channels, respectively. Pop III BBH mergers in NSCs are more massive than those from IBSE, so they dominate the Pop III SGWB below 20 Hz in most cases. Besides, the detection rate of Pop III BBH mergers involving at least one intermediate-mass BH above |$100\ \rm M_\odot$| by the Einstein Telescope is |$\sim 0.5\!-\!200\ \rm yr^{-1}$| in NSCs but remains below |$0.1\ \rm yr^{-1}$| for IBSE. [ABSTRACT FROM AUTHOR]

Several powerful flare events have been recorded because of long-term monitoring on the RT-22 radio telescope (Simeiz) of the galactic source G25.65 + 1.05 from 2000 to 2024. The amplitude of the most powerful flare increased rapidly and reached a record level for this source of 130 kJy. The orbital (7.5 years) and precessional (60 years) periods in the binary system of massive O5 class stars responsible for the occurrence of flares based on monitoring data have been presumably determined. Individual short flares, lasting no more than a month, presumably belonged to a maser in an unsaturated state. The shape of the central part of the maser line, near the maximum phase, suggests a single-component source responsible for the bulk of the increase in flux density. Thus, the most powerful kilomaser G25.65 + 1.05 in the water vapor line at frequency 22.2 GHz has been registered in the Galaxy. The possibility of detecting gravitational waves (GWs) coming from the massive stellar binary system is considered. The active galactic nucleus S 0528 + 134 was discovered in a search survey at a frequency of 8550 MHz in 1969 using the radio telescope RT-22 (Simeiz) at the Crimean Astrophysical Observatory—the study aimed to search for new active galactic nuclei (AGN). In this article, the goal was to determine the physical characteristics of the close binary system S 0528 + 134 for the subsequent assessment of the level of gravitational radiation coming from it. During long-term monitoring of the object at a frequency of 8 GHz, some powerful flares of flux density occurred, which made it possible to consider the source the most powerful emitter in the Universe. The presence of selected harmonic components in the flux density variations of S 0528 + 134 allowed obtaining the main physical characteristics of a binary system of supermassive black holes (SMBHs), which placed S 0528 + 134 in the rank of one of the most massive SMBHs. This AGN can also be considered the most powerful source for detecting GWs by using International Pulsar Timing Array gravitational wave detectors. [ABSTRACT FROM AUTHOR]

In this paper, we review the theoretical basis for generation of gravitational waves and the detection techniques used to detect a gravitational wave. To materialize this goal in a thorough way, we first start with a mathematical background for general relativity from which a clue for gravitational wave was conceived by Einstein. Thereafter, we give the classification scheme of gravitational waves such as (i) continuous gravitational waves, (ii) compact binary inspiral gravitational waves and (iii) stochastic gravitational wave. Necessary mathematical insight into gravitational waves from binaries is also dealt with which follows detection of gravitational waves based on the frequency classification. Ground-based observatories as well as space borne gravitational wave detectors are discussed in a length. We have provided an overview on the inflationary gravitational waves. In connection to data analysis by matched filtering there are a few highlights on the techniques, e.g. (i) random noise, (ii) power spectrum, (iii) shot noise and (iv) Gaussian noise. Optimal detection statistics for a gravitational wave detection is also in the pipeline of the discussion along with detailed necessity of the matched filter and deep learning. [ABSTRACT FROM AUTHOR]

Modified theories of gravity predict deviations from general relativity (GR) in the propagation of gravitational waves (GWs) across cosmological distances. A key prediction is that the GW luminosity distance will vary with redshift, differing from the electromagnetic (EM) luminosity distance due to varying effective Planck mass. We introduce a model-independent, data-driven approach to explore these deviations using multimessenger observations of dark standard sirens [binary black holes (BBH)]. By combining GW luminosity distance measurements from dark sirens with baryon acoustic oscillation measurements, BBH redshifts inferred from cross-correlation with spectroscopic or photometric galaxy surveys, and sound horizon measurements from the cosmic microwave background, we can make a data-driven test of GR (jointly with the Hubble constant) as a function of redshift. Using the multimessenger technique with the spectroscopic DESI galaxy survey, we achieve precise measurements of deviations in the effective Planck mass variation with redshift. For the Cosmic Explorer and Einstein Telescope (CEET), the best precision is approximately 3.6 per cent, and for LIGO–Virgo–KAGRA (LVK), it is 7.4 per cent at a redshift of |$\rm {z = 0.425}$|⁠. Additionally, we can measure the Hubble constant with a precision of about 1.1 per cent from CEET and 7 per cent from LVK over 5 yr of observation with a 75 per cent duty cycle. We also explore the potential of cross-correlation with photometric galaxy surveys from the Rubin Observatory, extending measurements up to a redshift of |$\rm {z \sim 2.5}$|⁠. This approach can reveal potential deviations from models affecting GW propagation using numerous dark standard sirens in synergy with DESI and the Rubin Observatory. [ABSTRACT FROM AUTHOR]

Both the Barrow and Tsallis δ entropies are one-parameter generalizations of the black-hole entropy, with the same microcanonical functional form. The ensuing deformation is quantified by a dimensionless parameter Δ , which in the case of Barrow entropy represents the anomalous dimension caused by quantum fluctuations over the horizon surface, while in Tsallis' case, it describes the deviation of the holographic scaling from extensivity. Here, we utilize the gravity-thermodynamics conjecture with the Barrow–Tsallis entropy to investigate the implications of the related modified Friedmann equations on the spectrum of primordial gravitational waves. We show that, with the experimental sensitivity of the next generation of gravitational wave detectors, such as the Big Bang Observer, it will be possible to discriminate deviations from the Λ CDM model up to Δ ≲ O (10 - 3) . In this limit, Barrow–Tsallis entropy reduces to a logarithmic correction to holographic scaling, which is nearly universally predicted by both entanglement entropy calculations in the UV regime and by several candidate theories of quantum gravity. Hence, our considerations and results are expected to have general validity in the quantum gravity framework. [ABSTRACT FROM AUTHOR]

Microseismic motion, ambient ground vibration caused by ocean waves, affects ground-based gravitational wave detectors. In this study, characteristics of the ocean waves including seasonal variations and correlation coefficients were investigated to obtain the significant wave heights at 13 coasts in Japan. The relationship between the ocean waves and the microseismic motion at the KAGRA site was also evaluated. As a result, it almost succeeded in explaining the microseismic motion at the KAGRA site by the principal components of the ocean wave data. One possible application of this study is microseismic forecasting, an example of which is also presented. [ABSTRACT FROM AUTHOR]

Third-generation (3G) gravitational-wave detectors such as the Einstein Telescope (ET) will observe binary black hole (BBH) mergers at redshifts up to z ∼ 100. However, an unequivocal determination of the origin of high-redshift sources will remain uncertain because of the low signal-to-noise ratio (S/N) and poor estimate of their luminosity distance. This study proposes a machine-learning approach to infer the origins of high-redshift BBHs. We specifically differentiate those arising from Population III (Pop. III) stars, which probably are the first progenitors of star-born BBH mergers in the Universe, and those originated from Population I-II (Pop. I–II) stars. We considered a wide range of models that encompass the current uncertainties on Pop. III BBH mergers. We then estimated the parameter errors of the detected sources with ET using the Fisher information-matrix formalism, followed by a classification using XGBOOST, which is a machine-learning algorithm based on decision trees. For a set of mock observed BBHs, we provide the probability that they belong to the Pop. III class while considering the parameter errors of each source. In our fiducial model, we accurately identify ≳10% of the detected BBHs that originate from Pop. III stars with a precision > 90%. Our study demonstrates that machine-learning enables us to achieve some pivotal aspects of the ET science case by exploring the origin of individual high-redshift GW observations. We set the basis for further studies, which will integrate additional simulated populations and account for further uncertainties in the population modeling. [ABSTRACT FROM AUTHOR]

Strongly gravitating systems can undergo unusual orbital trajectories. For example, "extreme mass ratio inspirals" (observable in the megahertz band by space-based gravitational wave detectors) can exhibit "zoom-whirl" orbits, which make complicated waveforms that are useful for mapping out the system's gravitational structure. Zoom-whirl behavior can be intuitively understood in the context of effective potentials, which should be familiar to students from classical orbital theory in mechanics. Here, we explore zoom-whirl orbits using effective potential theory around Schwarzschild black holes and present an interactive tool that can be used in pedagogical settings. Editor's Note: Newtonian orbital mechanics is clean and orderly, with bound orbits being closed ellipses. Relativistic effects spoil this simplicity; in a weak gravitational field (e.g., the solar system), general relativity famously predicts orbital precession. In the strong gravitational field near a black hole, orbits can become tumultuous, appearing chaotic and unpredictable. "Zoom-whirl orbits" are extreme examples of this behavior, where the orbiting object plunges close to the black hole, whirls around it many times, and then heads back out to a larger radius. The authors of this article demonstrate how these complex orbits (which are of interest in gravitational wave astronomy) can be understood using the undergraduate physics of effective potentials. Computational tools are also developed and are freely provided to anyone interested in studying gravitational wave signatures from such orbits. Readers interested in black holes and relativity (and who have been intimidated by advanced mathematical treatments elsewhere in the literature) will find this article fascinating and instructive. [ABSTRACT FROM AUTHOR]

Cosmic string networks are expected to generate a characteristic stochastic gravitational wave background that may be within the reach of current and upcoming gravitational wave detectors. A detection of this spectrum would provide invaluable information about the physics of the early universe, as it would allow us to probe the sequence of phase transitions that happened in the distant past. Here, I review the emission of gravitational waves by Nambu–Goto cosmic strings—thin cosmic strings that couple strongly to gravity only—and by superconducting strings—strings that carry electromagnetic currents. A comparison between the stochastic gravitational wave background predicted in these two very distinct string-forming scenarios reveals that this spectrum may have signatures that may allows us to discriminate between them observationally. The stochastic gravitational wave background generated by cosmic string networks may then enable us to uncover not only the energy-scale of the string-forming phase transition, but the underlying particle physics scenario as well. [ABSTRACT FROM AUTHOR]

Next-generation gravitational wave (GW) observatories are expected to measure GW signals with unprecedented sensitivity, opening new, independent avenues to learn about our Universe. The distance–redshift relation is a fulcrum for cosmology and can be tested with GWs emitted by merging binaries of compact objects, called standard sirens, thanks to the fact that they provide the absolute distance from the source. On the other hand, fluctuations of the intervening matter density field induce modifications on the measurement of luminosity distance compared to that of a homogeneous universe. Assuming that the redshift information is obtained through the detection of an electromagnetic counterpart, we investigate the impact that lensing of GWs might have in the inference of cosmological parameters. We treat lensing as a systematic error and check for residual bias on the values of the cosmological parameters. We do so by means of mock catalogues of bright siren events in different scenarios relevant to the Einstein Telescope. For our fiducial scenario, the lensing bias can be comparable to or greater than the expected statistical uncertainty of the cosmological parameters, although non-negligible fluctuations in the bias values are observed for different realizations of the mock catalogue. We also discuss some mitigation strategies that can be adopted in the data analysis. Overall, our work highlights the need to model lensing effects when using standard sirens as probes of the distance–redshift relation. [ABSTRACT FROM AUTHOR]

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Next-generation gravitational wave detectors (GWDs) like the Cosmic Explorer and Einstein Telescope require extensive vacuum tubing, necessitating cost-effective materials. This study explores the viability of mild steel as an alternative to austenitic stainless steel for ultrahigh vacuum beampipes, focusing on outgassing rates and surface chemistry after low-temperature bakeouts. Mild steels exhibit significantly lower hydrogen outgassing rates, below 10 − 14 mbar l s − 1 cm − 2 after bakeouts at 80 ° C for 48 h. While water vapor is the primary residual gas after such low-temperature bakeouts, repeated treatments reduce its outgassing rate and modify surface conditions so that such benefit is preserved after at least six months of exposure to laboratory air. These findings position mild steel as an economical and efficient material for future GWD beampipes. [ABSTRACT FROM AUTHOR]

Gravitational waveform predictions from 3D simulations of explosions of non-rotating massive stars with no magnetic fields have been extensively studied. However, the impact of magnetic fields and rotation on the core-collapse supernova gravitational-wave signal is not well understood beyond the core-bounce phase. Therefore, we perform four magnetohydrodynamical simulations of the explosion of a |$15\, {\rm M}_{\odot }$| star with the SFHx and SFHo equations of state. All of the models start with a weak magnetic field strength of |$10^{8}$|  G, and two of the models are rapidly rotating. We discuss the impact of the rotation and magnetic fields on the gravitational-wave signals. We find that the weak pre-collapse fields do not have a significant impact on the gravitational-wave signal amplitude. With rapid rotation, the f/g-mode trajectory can change in shape, and the dominant emission band becomes broader. We include the low-frequency memory component of the gravitational-wave signal from both matter motions and neutrino emission anisotropy. We show that including the gravitational waves from anisotropic neutrino emission increases the supernova gravitational-wave detection distances for the Einstein Telescope. The gravitational waves from anisotropic neutrino emission would also be detectable out to Mpc distances by a moon-based gravitational-wave detector. [ABSTRACT FROM AUTHOR]

On-orbit configuration estimation is one of the most important tasks for large-scale distributed spacecraft systems, yet incomplete measurement topologies limit the acquisition of partial inter-satellite relative navigation information. In this article, an on-orbit configuration estimation algorithm based on augmented sensing is proposed, which enables each spacecraft to extend the estimation range beyond the observation range without any communication overhead. Referring to the Bayesian inference process, the cooperative behavior of the large-scale distributed spacecraft system is applied to infer relative motion states of unobservable spacecrafts. Under the framework of scaled unscented transformations (SUT), we achieve high-accuracy configuration estimation for the large-scale distributed spacecraft system. Finally, the proposed algorithm is verified in a high-orbiting gravitational wave detector constellation with inter-satellite laser interferometers. [ABSTRACT FROM AUTHOR]

Transparent, inorganic composite materials are of broad interest, from structural components in astronomical telescopes and mirror supports to solid-state lasers, smart window devices, and gravitational wave detectors. Despite great progress in material synthesis, it remains a standing challenge to fabricate such transparent glass composites with high crystallinity (HC-TGC). Here, we demonstrate the co-solidification of a mixture of melts with a stark contrast in crystallization habit as an approach for preparing HC-TGC materials. The melts used in this approach are selected so that glass formation and crystal precipitation occur simultaneously and synergistically, avoiding the formation of interfacial cracks, residual pores, and delamination effects. Using this method, various unusual hybridized HC-TGC materials such as oxychloride, oxybromide, and oxyiodide composite systems were fabricated in dense, bulk shapes. These materials exhibit intriguing optical properties and neutron response-ability. Using such HC-TGC materials, we develop a neutron detector and demonstrate the application for efficient neutron monitoring and even single neutron detection. We expect that these findings may help to bring about a generation of fully inorganic, transparent composites with synergistic combinations of conventionally incompatible materials. Transparent composites are significant for various applications. Here, the authors propose the co-solidification strategy of crystal and glass melts for preparing transparent glass composite with high crystallinity and apply for neutron detection. [ABSTRACT FROM AUTHOR]

The noise caused by various temperature effects in the sensitive frequency band will cause errors in the detection results of space gravitational wave. Therefore, it is important to suppress the temperature noise of space-borne gravitational wave detectors. In this paper, a method is proposed to suppress temperature noise using a multi-layer composite structure consisting of low thermal conductivity material (R) and high specific heat capacity material (C). The arrangement in which heat flow passes through high specific heat capacity material first is "CR." The thermal simulation model is established to study the temperature noise transfer characteristics, and accuracy of the model is verified by experiments. The results show that the temperature noise of CRC is 90 % lower than that of RCR. The arrangement which heat flow passes through high specific heat capacity material first has an optimal high specific heat capacity material's proportion of 60 % to 70 %. When the number of composite layers is not less than 3 layers, the more the composite layers' number is, the better the suppression effect of multi-layer composite structure on temperature noise is. However, there is a limit to the way of obtaining noise reduction effect by increasing the number of layers. This paper provides a guidance for the suppression of temperature noise in gravitational wave detection. [ABSTRACT FROM AUTHOR]

The number of unstable combinations of elastic and Stokes optical modes of the LIGO Voyager gravitational wave detector, frequencies and spatial distributions of displacement vectors of elastic modes of the mirrors were calculated. The values of overlap factors for unstable modes up to ninth-order optical modes were calculated, taking into account the azimuthal condition of parametric instability. An analysis of the influence of the temperature dependence of the Young's modulus of the mirror material on the number of unstable modes in the Fabry–Perot cavity was performed. [ABSTRACT FROM AUTHOR]

The precise measurement of neutron star (NS) spins can provide important insight into the formation and evolution of compact binaries containing NSs. While traditional methods of NS spin measurement rely on pulsar observations, gravitational-wave detections offer a complementary avenue. However, determining component spins with gravitational waves is hindered by the small dimensionless spins of the NSs and the degeneracy in the mass and spin parameters. This degeneracy can be addressed by the inclusion of higher-order modes in the waveform, which are important for systems with unequal masses. This study shows the suitability of NS–black hole mergers, which are naturally mass-asymmetric, for precise NS spin measurements. We explore the effects of the black hole masses and spins, higher-mode content, inclination angles, and detector sensitivity on the measurement of NS spin. We find that networks with next-generation observatories like the Cosmic Explorer and the Einstein Telescope can distinguish NS dimensionless spin of 0.04 (0.1) from zero at 1 σ confidence for events within ∼350 (∼1000) Mpc. Networks with A+ and A♯ detectors achieve similar distinction within ∼30 (∼70) Mpc and ∼50 (∼110) Mpc, respectively. [ABSTRACT FROM AUTHOR]

We analyse the detection prospects for potential Primordial Black Hole Binary (PBHB) populations buried in the Stellar-Origin Black Hole Binary (SOBHB) population inferred by the LVK collaboration. We consider different PBHB population scenarios and several future Gravitational Wave (GW) detectors. To separate the PBHB component from the SOBHB one, we exploit the prediction that the PBHB merger rate does not decline as fast as the SOBHB one at high redshift. However, only a tiny fraction of PBHB events may be resolved individually, and the sub-threshold events may yield an undetectable Stochastic GW Background (SGWB). For this reason, we determine the statistical significance of the PBHB contributions in the number of resolvable events seen in future Earth-based detectors and the SGWB measured at LISA. We quantify them in the limit that SOBHB population uncertainties are small, as one may optimistically expect at the time that future detectors will operate. In general, we find the synergy between these probes will consistently help assess whether or not a sizeable PBHB population is present. [ABSTRACT FROM AUTHOR]

To be observed and analyzed by the network of current gravitational-wave detectors (LIGO, Virgo, KAGRA), and in anticipation of future third generation ground-based (Einstein Telescope, Cosmic Explorer) and space-borne (LISA) detectors, inspiralling compact binaries—binary star systems composed of neutron stars and/or black holes in their late stage of evolution prior the final coalescence—require high-accuracy predictions from general relativity. The orbital dynamics and emitted gravitational waves of these very relativistic systems can be accurately modelled using state-of-the-art post-Newtonian theory. In this article we review the multipolar-post-Minkowskian approximation scheme, merged to the standard post-Newtonian expansion into a single formalism valid for general isolated matter system. This cocktail of approximation methods (called MPM-PN) has been successfully applied to compact binary systems, producing equations of motion up to the fourth-post-Newtonian (4PN) level, and gravitational waveform and flux to 4.5PN order beyond the Einstein quadrupole formula. We describe the dimensional regularization at work in such high post-Newtonian calculations, for curing both ultra-violet and infra-red divergences. Several landmark results are detailed: the definition of multipole moments, the gravitational radiation reaction, the conservative dynamics of circular orbits, the first law of compact binary mechanics, and the non-linear effects in the gravitational-wave propagation (tails, iterated tails and non-linear memory). We also discuss the case of compact binaries moving on eccentric orbits, and the effects of spins (both spin-orbit and spin–spin) on the equations of motion and gravitational-wave energy flux and waveform. [ABSTRACT FROM AUTHOR]

This article explores the design and optimization of nanodisk metasurfaces for achieving high reflectivity at a defined wavelength. The telecom wavelength of 1550 nm is particularly focused, selected for its potential applications in next‐generation gravitational wave detectors. At this wavelength, the research goes toward the development of thin, low‐loss, high‐reflective coatings, where the metasurface can be chosen as an alternative. An optimization process for the dimensional parameters of nanodisks is proposed based on a systematic tuning approach, which facilitates the realization of various configurations of high‐reflective metasurfaces. The concept of the "magnetic mirror effect" is examined in detail, where the magnetic dipole resonance aligns with the anapole state. Additionally, high reflectivity at the electric dipole resonance ("electric mirror effect") and at the excitation of several multipole moments is explored, including high‐order modes. This variety of configurations affords more flexibility in the phase manipulation of the reflected beam. Furthermore, the potential experimental realization of mirror effects is discussed by exploring the structure in the surrounding medium with a refractive index of nd = 1.4. This research platform provides a promising tool for the fabrication of high‐reflective nanodisk metasurfaces and demonstrates its applicability across various fields. [ABSTRACT FROM AUTHOR]

Binary-black-hole (BBH) mergers can take place close to a supermassive black hole (SMBH) while being in a bound orbit around the SMBH. In this paper, we study such bound triple systems and show that including the strong gravity effects of describing the SMBH with a Kerr metric can significantly modify the dynamics, as compared to a Newtonian point particle description of the SMBH. We extract the dynamics of the system, using a quadrupole approximation to the tidal forces due to the SMBH. We exhibit how the gyroscope precession is built into this dynamics, and find the secular Hamiltonian by both averaging over the inner and outer orbits, the latter being the orbit of the BBH around the SMBH. We study the long-time-scale dynamics, including the periastron precession and gravitational wave (GW) radiation reaction of the binary system, finding that the strong gravity effects of the SMBH can enhance the von Zeipel–Lidov–Kozai mechanism, resulting in more cycles, higher maximum eccentricity, and thereby a shorter merger time, particularly when the binary is close to, or at, the innermost stable orbit of the SMBH. We end with an analysis of the peak frequency of the GW emission from the binary system, highlighting possible observable signatures in the Einstein Telescope and Laser Interferometer Space Antenna frequency bands. [ABSTRACT FROM AUTHOR]

The ground-based gravitational wave (GW) detectors LIGO and Virgo have enabled the birth of multi-messenger GW astronomy via the detection of GWs from merging stellar-mass black holes (BHs) and neutron stars (NSs). GW170817, the first binary NS merger detected in GWs and all bands of the electromagnetic spectrum, is an outstanding example of the impact that GW discoveries can have on multi-messenger astronomy. Yet, GW170817 is only one of the many and varied multi-messenger sources that can be unveiled using ground-based GW detectors. In this contribution, we summarize key open questions in the astrophysics of stellar-mass BHs and NSs that can be answered using current and future-generation ground-based GW detectors, and highlight the potential for new multi-messenger discoveries ahead. [ABSTRACT FROM AUTHOR]