Keywords

I estimate the frequencies of gravitational waves from jittering jets that explode core collapse supernovae (CCSNe) to crudely be 5–30 Hz, and with strains that might allow detection of Galactic CCSNe. The jittering jets explosion mechanism (JJEM) asserts that most CCSNe are exploded by jittering jets that the newly born neutron star (NS) launches within a few seconds. According to the JJEM, instabilities in the accreted gas lead to the formation of intermittent accretion disks that launch the jittering jets. Earlier studies that did not include jets calculated the gravitational frequencies that instabilities around the NS emit to have a peak in the crude frequency range of 100–2000 Hz. Based on a recent study, I take the source of the gravitational waves of jittering jets to be the turbulent bubbles (cocoons) that the jets inflate as they interact with the outer layers of the core of the star at thousands of kilometers from the NS. The lower frequencies and larger strains than those of gravitational waves from instabilities in CCSNe allow future, and maybe present, detectors to identify the gravitational wave signals of jittering jets. Detection of gravitational waves from local CCSNe might distinguish between the neutrino-driven explosion mechanism and the JJEM.

In this work, we present the probabilities of mergers of binary black holes (BBHs) and binary neutron stars (BNSs) as functions of stellar mass, metallicity, specific star formation rate (sSFR), and age for galaxies with redshift z ≤ 0.1. Using the binary-star evolution (BSE) code and some fitting formulae, we construct a phenomenological model of cosmic gravitational wave (GW) merger events. By using the Bayesian analysis method and the observations from Advanced LIGO and Virgo, we obtain the relevant parameters of the phenomenological model (such as the maximum black hole mass is ${93}_{-22}^{+73}\,{M}_{\odot }$). Combining the above model results with the galaxy catalog given by the EMERGE empirical galaxy model, we find the normalized probability of occurrence of a merger event varying with ${\mathrm{log}}_{10}(\mathrm{sSFR}/{\mathrm{yr}}^{-1})$ for galaxies with z ≤ 0.1 is different from that in previous studies, that is, two peaks exist in this work while there is only one peak (log₁₀(sSFR/yr ⁻¹) = −10) in the previous work. The sSFR value corresponding to the new peak is log₁₀(sSFR/yr ⁻¹) = −12 and in line with the value (${\mathrm{log}}_{10}(\mathrm{sSFR}/{\mathrm{yr}}^{-1})=-{12.65}_{-0.66}^{+0.44}$) of NGC 4493, the host galaxy of BNS merger event GW170817. The new peak is caused by today's quenched galaxies, which give a large contribution to the total SFR at high redshift in the EMERGE empirical galaxy model. Moreover, we find that the BNS mergers are most likely detected in galaxies with age ∼11 Gyr, which is greater than previous results (6−8 Gyr) and close to the age of NGC 4993, ${13.2}_{-0.9}^{+0.5}$ Gyr.

Observing and timing a group of millisecond pulsars with high rotational stability enables the direct detection of gravitational waves (GWs). The GW signals can be identified from the spatial correlations encoded in the times-of-arrival of widely spaced pulsar-pairs. The Chinese Pulsar Timing Array (CPTA) is a collaboration aiming at the direct GW detection with observations carried out using Chinese radio telescopes. This short article serves as a "table of contents" for a forthcoming series of papers related to the CPTA Data Release 1 (CPTA DR1) which uses observations from the Five-hundred-meter Aperture Spherical radio Telescope. Here, after summarizing the time span and accuracy of CPTA DR1, we report the key results of our statistical inference finding a correlated signal with amplitude $\mathrm{log}{A}_{{\rm{c}}}=-14.4{\,}_{-2.8}^{+1.0}$ for spectral index in the range of α ∈ [ − 1.8, 1.5] assuming a GW background (GWB) induced quadrupolar correlation. The search for the Hellings–Downs (HD) correlation curve is also presented, where some evidence for the HD correlation has been found that a 4.6σ statistical significance is achieved using the discrete frequency method around the frequency of 14 nHz. We expect that the future International Pulsar Timing Array data analysis and the next CPTA data release will be more sensitive to the nHz GWB, which could verify the current results.

GW170817 is the unique gravitational-wave (GW) event associated with the electromagnetic (EM) counterpart GRB 170 817A. NGC 4993 is identified as the host galaxy of GW170817/GRB 170 817A. In this paper, we focus on the spatially resolved properties of NGC 4993. We present the photometric results from the comprehensive data analysis of the high spatial-resolution images in the different optical bands. The morphological analysis reveals that NGC 4993 is a typical early-type galaxy without significant remnants of a major galaxy merger. The spatially resolved stellar population properties of NGC 4993 suggest that the galaxy center has passive evolution with the outskirt formed by gas accretion. We derive the merging rate of the compact object per galaxy by a co-evolution scenario of a supermassive black hole and its host galaxy. If the galaxy formation is at redshift 1.0, the merging rate per galaxy is from 3.2 × 10⁻⁴ to 7.7 × 10⁻⁵ within the merging decay time from 1.0 to 5.0 Gyr. The results provide vital information for ongoing GW EM counterpart detections. The Hubble space telescope data analysis presented in this paper can be also applied to Chinese Space Station Telescope research in the future.

The braking indices of pulsars may contain important information about the internal physics of neutron stars (NSs), such as neutron superfluidity and internal magnetic fields. As a subsequent paper of Cheng et al., we perform the same analysis as that done in the previous paper to other young pulsars with a steady braking index, n. Combining the timing data of these pulsars with the theory of magnetic field decay, and using their measured magnetic tilt angles, we can set constraints on the number of precession cycles, ξ, which represents the interactions between superfluid neutrons and other particles in the NS interior. For the pulsars considered in this paper, the results show that ξ is within the range of a few ×10³ to a few ×10⁶. Interestingly, for the Crab and Vela pulsars, the constraints on ξ obtained with our method are generally consistent with that derived from modeling of the glitch rise behaviors of the two pulsars. Furthermore, we find that the internal magnetic fields of pulsar with n < 3 may be dominated by the toroidal components. Our results may not only help to understand the interactions between the superfluid neutrons and other particles in the interior of NSs but also be important for the study of continuous gravitational waves from pulsars.

The range of the U bosonic coupling constants in neutron star matter is a very interesting but still unsolved problem which has multifaceted influences in nuclear physics, particle physics, astrophysics and cosmology. The combination of the theoretical numerical simulation and the recent observations provides a very good opportunity to solve this problem. In the present work, the range of the U bosonic coupling constants is inferred based on the three relations of the mass–radius, mass-frequency and mass-tidal deformability in neutron stars containing hyperons using the GM1, TM1 and NL3 parameter sets under the two flavor symmetries of SU(6) and SU(3) in the framework of the relativistic mean field theory. Combined with observations from PSRs J1614-2230, J0348+0432, J2215-5135, J0952-0607, J0740+6620, J0030-0451, J1748-2446ad, XTE J1739-285, GW170817 and GW190814 events, our numerical results show that the U bosonic coupling constants may tend to be within the range from 0 to 20 GeV⁻² in neutron star containing hyperons. Moreover, the numerical results of the three relations obtained by the SU(3) symmetry are better in accordance with observation data than those obtained by the SU(6) symmetry. The results will help us to improve the strict constraints of the equation of state for neutron stars containing hyperons.

The binary population in field stars and star clusters contributes to the formation of gravitational wave (GW) sources. However, the fraction of compact-object binaries (CBs), which is an important feature parameter of binary populations, is still difficult to measure and very uncertain. This paper predicts the fractions of important CBs and semi-compact object binaries (SCBs) making use of an advanced stellar population synthesis technique. A comparison with the result of N-body simulation is also presented. It is found that most CBs are formed within about 500 Myr after the starburst. The fractions of CBs and SCBs are demonstrated to correlate with stellar metallicity. The higher the metallicity becomes, the smaller the fraction of black hole binaries (BHBs), neutron star binaries (NSBs) and SCBs. This suggests that the GW sources of BHBs and NSBs are more likely to form in metal-poor environments. However, the fraction of black hole-neutron star binaries is shown to be larger for metal-rich populations on average.

The observed electromagnetic radiation from some long and short gamma-ray bursts, and neutron stars (NSs), and the theoretical models proposed to interpret these observations together point to a very interesting but confusing problem, namely, whether fall-back accretion could lead to dipole field decay of newborn NSs. In this paper, we investigate the gravitational wave (GW) radiation of newborn magnetars with a fall-back disk formed in both the core-collapse of massive stars and the merger of binary NSs. We make a comparison of the results obtained with and without fall-back accretion-induced dipole-field decay (FADD) involved. Depending on the fall-back parameters, initial parameters of newborn magnetars, and models used to describe FADD, FADD may indeed occur in newborn magnetars. Because of the low dipole fields caused by FADD, the newborn magnetars will be spun up to higher frequencies and have larger masses in comparison with the non-decay cases. Thus the GW radiation of newborn accreting magnetars would be remarkably enhanced. We propose that observation of GW signals from newborn magnetars using future GW detectors may help to reveal whether FADD could occur in newborn accreting magnetars. Our model is also applied to the discussion of the remnant of GW170817. From the post-merger GW searching results of Advanced LIGO and Advanced Virgo we cannot confirm the remnant is a low-dipole-field long-lived NS. Future detection of GWs from GW170817-like events using more sensitive detectors may help to clarify the FADD puzzle.

The space-borne gravitational wave detectors will observe a large population of double white dwarf binaries in the Milky Way. However, the search for double white dwarfs in the gravitational wave data will be time-consuming due to the large number of templates involved and antenna response calculation. In this paper, we implement an iterative combinatorial algorithm to search for double white dwarfs in MLDC-3.1 data. To quickly determine the rough parameters of the target sources, the following algorithms are adopted in a coarse search process: (1) using the downsampling method to reduce the number of original data points; (2) using the undersampling method to speed up the generation of a single waveform template; (3) using the stochastic template bank method to quickly construct the waveform template bank while achieving high coverage of the parameter space; (4) combining the FFT acceleration algorithm with the stochastic template bank to reduce the calculation time of a single template. A fine search process is applied to further determine the parameters of the signals based on the coarse search, for which we adopt the particle swarm optimization. Finally, we detect ${ \mathcal O }({10}^{4})$ double white dwarf signals, validating the feasibility of our method.

Motivated by the determination of black hole masses with gravitational-wave observations, we calculate the evolution of massive stars through presupernova stages and obtain the mass distribution of black holes. In the first part, we calculate the evolution of He stars with masses of 30–120 M_⊙. We study in detail how convective carbon shell burning controls pair-instability pulsations before and during oxygen burning and determine their final fates. In the second part, we calculate the evolution of H-rich stars with initial masses of 13–80 M_⊙ until Fe core collapse and obtain the possible black hole mass range by applying the criterion of the compactness parameters. From these models, we predict the mass distribution of black holes for stars that undergo Fe core collapse and pair-instability pulsation. The predicted masses for black holes range from 4.2 to 46 M_⊙, which are consistent with the gravitational-wave observations.