Accuracy of numerical relativity waveforms with respect to space-based gravitational wave detectors

As with the laser interferometer gravitational-wave observatory(LIGO),the matched filtering technique will be critical to the data analysis of gravitational wave detection by space-based detectors,including LISA,Taiji and Tianqin.Waveform templates are the basis for such matched filtering techniques.To construct ready-to-use waveform templates,numerical relativity waveforms are a starting point.Therefore,the accuracy issue of numerical relativity waveforms is critically important.There are many investigations regarding this issue with respect to LIGO.But unfortunately there are few results on this issue with respect to space-based detectors.The current paper investigates this problem.Our results indicate that the existing numerical relativity waveforms are as accurate as 99%with respect to space-based detectors,including LISA,Taiji and Tianqin.Such an accuracy level is comparable to that with respect to LIGO.

Evidence for False Vacuum States inside the Cores of Massive Pulsars and the Ramification on the Measurements of Their True Masses

Based on the theory and observations of glitching pulsars, we show that the ultra-cold supranuclear dense matter inside the cores of massive pulsars should condensate in vacua, as predicated by non-perturbative QCD. The trapped matter here forms false vacuums embedded in flat spacetimes and completely disconnected from the outside world. Although the vacuum expectation value here vanishes, the masses and sizes of these incompressible superfluid cores are set to grow with cosmic times, in accord with the Onsager-Feynman superfluidity analysis. We apply our scenario to several well-studied pulsars, namely the Crab, Vela, PSR J0740+6620 and find that the trapped mass-contents in their cores read {0.15,0.55,0.64}, implying that their true masses are {1.55,2.35,2.72} , respectively. Based thereon, we conclude that: 1) The true masses of massive pulsars and neutron stars are much higher than detected by direct observations and, therefore, are unbounded from above, 2) The remnant of the merger event in GW170817 should be a massive NS harbouring a core with 1.66 .

Gravitational Radiation of Binaries Coalescence into Intermediate Mass Black Holes

This paper discusses the gravitation waveforms of binaries coalescence into intermediate mass black holes(about 30 times of the solar mass).We focus on the non-spinning intermediate mass black hole located less than 100 Mpc from earth.By comparing two simulation waveforms(effective one body numerical relativity waveform(EOBNR),phenomenological waveform),we discuss the relationship between the effective distance and frequency;and through analyzing large amounts of data in event,we find that the phenomenological waveform is much smoother than EOBNR waveform,and has higher accuracy at the same effective distance.

Why the Spacetime Embedding Incompressible Cores of Pulsars Must Be Conformally Flat?

The multi-messenger observations of the merger event in GW170817 did not rule out the possibility that the remnant might be a dynamically stable neutron star with . Based on this and other recent events, I argue that the universal maximum density hypothesis should be revived. Accordingly, the central densities in the cores of ultra-compact objects must be upper-limited by the critical density number ncr, beyond which supranuclear dense matter becomes purely incompressible. Based on the spacetime-matter coupling in GR, it is shown that the topology of spacetime embedding incompressible quantum fluids with n=ncr must be Minkowski flat, which implies that spacetime at the background of ultra-compact objects should be bimetric.

The Remnant of GW170817: A Trapped Neutron Star with a Massive Incompressible Superfluid Core

Our bimetric spacetime model of glitching pulsars is applied to the remnant of GW170817. Accordingly, pulsars are born with embryonic incompressible superconducting gluon-quark superfluid cores (SuSu-matter) that are embedded in Minkowski spacetime, whereas the ambient compressible and dissipative media (CDM) are imbedded in curved spacetime. As pulsars cool down, the equilibrium between both spacetime is altered, thereby triggering the well-observed glitch phenomena. Based thereon and assuming all neutron stars (NSs) to be born with the same initial mass of , we argue that the remnant of GW170817 should be a relatively faint NS with a massive central core made of SuSu-matter. The effective mass and radius of the remnant are predicted to be and Rrem=10.764 Km, whereas the mass of the enclosed SuSu-core is . Here, about 1/2Mcore is an energy enhancement triggered by the phase transition of the gluon-quark-plasma from the microscopic into macroscopic scale. The current compactness of the remnant is , but predicted to increase as the CDM and cools down, rendering the remnant an invisible dark energy object, and therefore to an excellent black hole candidate.

New results on the dynamics of critical collapse

We study the dynamics of the critical collapse of a spherically symmetric scalar field.Approximate analytic expressions for the metric functions and matter field in the large-radius region are obtained.In the central region,owing to the boundary conditions,the equation of motion for the scalar field is reduced to the flat-spacetime form.

Energy in critical collapse

We study the energy issue in critical collapse.It is found that in critical collapse,the contribution from the material energy is greater than that from the gravitational energy.The quantity m/r plays an important role in identifying the formation of an apparent horizon in gravitational collapse,where m is the Misner-Sharp mass and r is the areal radius.We observe that in critical collapse,the maximum value of m/r fluctuates between 2/15 and 4/15.This denotes a large gap between critical collapse and black hole formation for which the criterion is m/r=1/2.

The Gravitational-wave physics Ⅱ: Progress

It has been a half-decade since the first direct detection of gravitational waves, which signifies the coming of the era of the gravitational-wave astronomy and gravitational-wave cosmology. The increasing number of the detected gravitational-wave events has revealed the promising capability of constraining various aspects of cosmology, astronomy, and gravity. Due to the limited space in this review article, we will briefly summarize the recent progress over the past five years, but with a special focus on some of our own work for the Key Project "Physics associated with the gravitational waves" supported by the National Natural Science Foundation of China. In particular,(1) we have presented the mechanism of the gravitational-wave production during some physical processes of the early Universe, such as inflation, preheating and phase transition, and the cosmological implications of gravitational-wave measurements;(2) we have put constraints on the neutron star maximum mass according to GW170817 observations;(3) we have developed a numerical relativity algorithm based on the finite element method and a waveform model for the binary black hole coalescence along an eccentric orbit.

IMEX Evolution of Scalar Fields on Curved Backgrounds

Inspiral of binary black holes occurs over a time-scale of many orbits,far longer than the dynamical time-scale of the individual black holes.Explicit evolutions of a binary system therefore require excessively many time-steps to capture interesting dynamics.We present a strategy to overcome the Courant-Friedrichs-Lewy condition in such evolutions,one relying on modern implicit-explicit ODE solvers and multidomain spectral methods for elliptic equations.Our analysis considers the model problem of a forced scalar field propagating on a generic curved background.Nevertheless,we encounter and address a number of issues pertinent to the binary black hole problem in full general relativity.Specializing to the Schwarzschild geometry in KerrSchild coordinates,we document the results of several numerical experiments testing our strategy.