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Abstract As gravitational wave (GW) astronomy has entered an era of routine detections, it becomes increasingly important to precisely measure the physical parameters of individual events and infer population properties. Eccentricity is a key observable, suggesting that binaries form in a dense stellar environment through dynamical encounters. This work performs the first matched-filtering search for GWs from eccentric binary black holes (BBHs) covering the mass range [5, 200]M_⊙and eccentricity at 20 Hz up to 0.5 with a newly developed effective-one-body waveform model. Throughout the third observation run of LIGO, Virgo, and KAGRA, we identify 28 BBH events with a false alarm rate (FAR) below once per 100 yr, all of which were previously reported in the third Gravitational-wave Transient Catalog and fourth Open Gravitational-wave Catalog. Additional candidates with FARs between once per 1 and 100 yr are also reported. We perform an injection campaign to characterize the sensitive volume time of our search pipeline. Assuming that none of the eccentric BBH events were missed by previous searches, our results provide constraints on the event rate of eccentric BBHs in the mass range [5, 30]M_⊙. For a 30–30M_⊙BBH with eccentricity 0.5, the event rate is limited to less than 0.06 Gpc⁻³yr⁻¹; this marks a 1 order of magnitude improvement for sensitive volume compared with the previous search with a minimally modeled algorithm without using templates. 

The possible formation histories of neutron star binaries remain unresolved by current gravitational-wave catalogs. The detection of an eccentric binary system could be vital in constraining compact binary formation models. We present the first search for aligned spin eccentric neutron star-black hole binaries (NSBH) and the most sensitive search for aligned-spin eccentric binary neutron star (BNS) systems using data from the third observing run of the advanced LIGO and advanced Virgo detectors. No new statistically significant candidates are found; we constrain the local merger rate for specific astrophysical models to be less than $150{\mathrm{Gpc}}^{-3}{\mathrm{yr}}^{-1}$for binary neutron stars in the field, and, 50, 100, and $70{\mathrm{Gpc}}^{-3}{\mathrm{yr}}^{-1}$for neutron star-black hole binaries in globular clusters, hierarchical triples and nuclear clusters, respectively, at the 90% confidence level if we assume that no sources have been observed from these populations. We predict the capabilities of upcoming and next-generation observatory networks; we investigate the ability of three LIGO ( ${\mathrm{A}}^{\#}$) detectors and Cosmic Explorer $\mathrm{CE}\left(20\mathrm{km}\right)+\mathrm{CE}\left(40\mathrm{km}\right)$to use eccentric binary observations for determining the formation history of neutron star binaries. We find that 2–100 years of observation with three ${\mathrm{A}}^{\#}$observatories are required before we observe clearly eccentric NSBH binaries; this reduces to only 10 days–1 year with the CE detector network. CE will observe tens to hundreds of measurably eccentric binaries from each of the formation models we consider. 

Abstract Most observed neutron stars have masses around 1.4M_⊙, consistent with current formation mechanisms. To date, no subsolar-mass neutron star has been observed. Observing one would provide crucial constraints on the nuclear equation of state, unveil a new neutron star population, and advance understanding of their formation mechanisms. We present the first targeted search for tidally deformed subsolar-mass binary neutron stars (BNSs), with primary masses ranging from 0.1 to 2M_⊙and secondary masses from 0.1 to 1M_⊙, using data from the third observing run of the Advanced LIGO and Virgo gravitational-wave detectors. We account for the tidal deformabilities of up toO(10⁴) of these systems, as low-mass neutron stars are more easily distorted by their companions. Previous searches that neglect tidal deformability lose sensitivity to low-mass sources, potentially missing more than ∼30% of detectable signals from a system with a chirp mass of 0.6M_⊙binaries. No statistically significant detections were made. In the absence of a detection, we place a 90% confidence upper limit on the local merger rate for subsolar BNSs, constraining it to be <6.4 × 10⁴Gpc⁻³yr⁻¹for a chirp mass of 0.2M_⊙and <2.2 × 10³Gpc⁻³yr⁻¹for 0.7M_⊙. With future upgrades to detector sensitivity, development of next-generation detectors, and ongoing improvements in search pipelines, constraints on the minimum mass of neutron stars will improve, providing the potential to constrain the nuclear equation of state, reveal new insights into neutron star formation channels, and potentially identify new classes of stars. 

Abstract Detecting gravitational waves (GWs) from coalescing compact binaries has become routine with ground-based detectors like Advanced LIGO and Advanced Virgo. However, beyond standard sources such as binary black holes and neutron stars and neutron star black holes, no exotic sources revealing new physics have been discovered. Detecting ultracompact objects, such as subsolar mass (SSM), offers a promising opportunity to explore diverse astrophysical populations. However, searching for these objects using standard matched-filtering techniques is computationally intensive due to the dense parameter space involved. This increasing computational demand not only challenges current search methodologies but also poses a significant obstacle for third-generation (3G) ground-based GW detectors. In the 3G detectors, signals are expected to be observed for tens of minutes and detection rates to reach one per minute. This requires efficient search strategies to manage the computational load of long-duration signal search. In this paper, we demonstrate how hierarchical search strategies can address the computational challenges associated with detecting long-duration signals in current detectors and the 3G era. Using SSM searches as an example, we show that optimizing data sampling rates and adjusting the number of templates in matched filtering at each stage of low-frequency searches can improve the signal-to-noise ratio by 6% and detection volume by 10%–20%. This sensitivity improvement is achieved with a 2.5-fold reduction in computational time compared to standard PyCBC searches. We also discuss how this approach could be adapted and refined for searches involving eccentric and precessing binaries with future detectors. 

Abstract The next generation of ground-based interferometric gravitational wave detectors will observe mergers of black holes and neutron stars throughout cosmic time. A large number of the binary neutron star merger events will be observed with extreme high fidelity, and will provide stringent constraints on the equation of state of nuclear matter. In this paper, we investigate the systematic improvement in the measurability of the equation of state with increase in detector sensitivity by combining constraints obtained on the radius of a $1.4{\mathrm{M}}_{\odot }$neutron star from a simulated source population. Since the measurability of the equation of state depends on its stiffness, we consider a range of realistic equations of state that span the current observational constraints. We show that a single 40 km Cosmic Explorer detector can pin down the neutron star radius for a soft, medium and stiff equation of state with a precision of 10 m within a decade, whereas the current generation of ground-based detectors like the Advanced LIGO-Virgo network would take $O\left({10}^5\right)$years to do so for a soft equation of state. 

Abstract Gravitational wave searches are crucial for studying compact sources such as neutron stars and black holes. Many sensitive modeled searches use matched filtering to compare gravitational strain data to a set of waveform models known as template banks. We introduce a new stochastic placement method for constructing template banks, offering efficiency and flexibility to handle arbitrary parameter spaces, including orbital eccentricity, tidal deformability, and other extrinsic parameters. This method can be computationally limited by the ability to compare proposal templates with the accepted templates in the bank. To alleviate this computational load, we introduce the use of inner product inequalities to reduce the number of required comparisons. We also introduce a novel application of Gaussian Kernel Density Estimation to enhance waveform coverage in sparser regions. Our approach has been employed to search for eccentric binary neutron stars, low-mass neutron stars, primordial black holes, and supermassive black hole binaries. We demonstrate that our method produces self-consistent banks that recover the required minimum fraction of signals. For common parameter spaces, our method shows comparable computational performance and similar template bank sizes to geometric placement methods and stochastic methods, while easily extending to higher-dimensional problems. The time to run a search exceeds the time to generate the bank by a factor of $\mathcal{O}\left({10}^5\right)$for dedicated template banks, such as geometric, mass-only stochastic, and aligned spin cases, $\mathcal{O}\left({10}^4\right)$for eccentric and $\mathcal{O}\left({10}^3\right)$for the tidal deformable bank. With the advent of efficient template bank generation, the primary area for improvement is developing more efficient search methodologies. 

ABSTRACT Searches for gravitational waves from compact binary mergers, which to date have reported ∼100 observations, have previously ignored binaries whose components are consistent with the mass of neutron stars (1–2 M⊙) and have high dimensionless spin >0.05. While previous searches targeted sources that are representative of observed neutron star binaries in the Galaxy, it is already known that neutron stars can regularly be spun up to a dimensionless spin of ∼0.4, and in principle reach up to ∼0.7 before breakup would occur. Furthermore, there may be primordial black hole binaries or exotic formation mechanisms to produce light black holes. In these cases, it is possible for the binary constituent to be spun up beyond that achievable by a neutron star. A single detection of this type of source would reveal a novel formation channel for compact binaries. To determine whether there is evidence for any such sources, we use pycbc to conduct a targeted search of LIGO and Virgo data for light compact objects with high spin. Our analysis detects previously known observations GW170817 and GW200115; however, we report no additional mergers. The most significant candidate, not previously known, is consistent with the noise distribution, and so we constrain the merger rate of spinning light binaries.