arXiv subjects

Dongze Sun

Publications and source records attributed to Dongze Sun.

9 recordsLinked to original sources

arXiv2026

Convergence of post-Newtonian for quasi-circular non-precessing comparable mass ratios BBHs

Post-Newtonian (PN) theory provides the analytic foundation for modeling the early inspiral of binary black holes. However, as an asymptotic series, successive PN orders do not necessarily improve agreement with the full nonlinear dynamics. While this has been explored in the extreme-mass-ratio limit, comparable-mass systems most relevant to current observations have not been benchmarked as systematically at high PN order. We study the convergence of the PN series for non-spinning and quasi-circular systems by comparing the PN energy flux at future null infinity to a long, high-accuracy numerical relativity (NR) simulation. To enable a gauge-consistent comparison, we place both descriptions in the same BMS frame and calibrate the intrinsic PN parameters by fitting to the NR waveform in the early inspiral. We find that for orbital velocities $v\lesssim0.45$, higher PN orders continue to reduce the PN--NR flux discrepancy, with (incomplete) 6PN providing the best agreement among the orders considered. The improvement with PN order is non-monotonic with local extrema around 2.5PN and 4PN. This implies that the optimal truncation order of the PN series cannot be identified from the first local minimum in the energy flux residuals, contrary to suggestions in earlier work. As $v$ approaches $\sim 0.5$ near the innermost circular orbit, higher PN orders no longer improve the agreement between NR and PN, indicating a loss of convergence. These results motivate continued high-order PN calculations and clarify the NR accuracy needed to validate them.

gr-qc↗

arXiv2025

Parameter matching between horizon quasi-local and point-particle definitions at 1PN for quasi-circular and non spinning BBH systems in harmonic gauge

We investigate how commonly used parameter definitions in Post-Newtonian (PN) theory compare with those from Numerical Relativity (NR) for binary black hole (BBH) systems. In NR, masses and spins of each companion are measured quasi-locally from apparent horizon geometry, whereas in PN they are attributes of point particles defined via asymptotic matching in body zones. Although these definitions coincide in the infinite-separation limit, they could differ by finite-separation corrections that matter for precision modeling. Working entirely in harmonic gauge, we perform asymptotic matching between each companion's inner zone metric -- obtained from black hole perturbation theory -- and the PN two-body metric, and construct the coordinate transformation that preserves the gauge in the strong field region. We solve perturbatively for the apparent horizon (AH) on a group of harmonic inertial time slice and compute its quasi-local areal mass from the horizon geometry. Then we establish the leading order matching between quasi-local (AH based) and PN (point-particle) parameter definitions in harmonic gauge. We find that on a horizon penetrating harmonic slicing, the AH quasi-local mass agrees with the PN point-particle mass at 1PN order. For generic harmonic slicings that deviate from the horizon penetrating condition by a 1PN order perturbation, the AH mass differs from the PN mass also by a 1PN correction. This parameter matching is crucial for hybridizing PN and NR waveforms and for providing better initial conditions in NR and Cauchy-Characteristic Evolution (CCE) simulations. The framework provides a bridge between different descriptions of BBH systems, and it can be extended to spinning and eccentric cases and more general NR gauges.

gr-qc↗

arXiv2025

Gauge Boundary conditions to mitigate center-of-mass drift in BBH simulations

Long-term numerical relativity (NR) simulations of binary black hole (BBH) systems in the Spectral Einstein Code (SpEC) code exhibit an unexpected exponential drift of the center-of-mass (CoM) away from the simulation's origin. In our work, we analyze this phenomenon and demonstrate that it is not a physical effect but rather a manifestation of a gauge artifact. The origin of this drift is the reflection of the gauge waves off the outer boundary of the computational domain. These reflections are introduced by inaccuracies in the gauge boundary condition, specifically, the application of the Sommerfeld condition to the time derivative of the gauge fields. Such an approach fails to completely suppress or correctly absorb the outgoing modes, thereby generating artificial feedback into the simulation. To mitigate this problem, we introduce a modified boundary condition that incorporates an explicit CoM correction source term designed to counteract the CoM motion. Our numerical experiments, performed with the SpEC code, reveal that this new boundary treatment reduces the CoM drift by several orders of magnitude compared to the standard implementation, and does not introduce any unwanted physical artifacts.

gr-qc↗

arXiv2025

The SXS Collaboration's third catalog of binary black hole simulations

We present a major update to the Simulating eXtreme Spacetimes (SXS) Collaboration's catalog of binary black hole simulations. Using highly efficient spectral methods implemented in the Spectral Einstein Code (SpEC), we have nearly doubled the total number of binary configurations from 2,018 to 3,756. The catalog now densely covers the parameter space with precessing simulations up to mass ratio $q=8$ and dimensionless spins up to $|\vec{\chi}|\le0.8$ with near-zero eccentricity. The catalog also includes some simulations at higher mass ratios with moderate spin and more than 250 eccentric simulations. We have also deprecated and rerun some simulations from our previous catalog (e.g., simulations run with a much older version of SpEC or that had anomalously high errors in the waveform). The median waveform difference (which is similar to the mismatch) between resolutions over the simulations in the catalog is $4\times10^{-4}$. The simulations have a median of 22 orbits, while the longest simulation has 148 orbits. We have corrected each waveform in the catalog to be in the binary's center-of-mass frame and exhibit gravitational-wave memory. We estimate the total CPU cost of all simulations in the catalog to be 480,000,000 core-hours. We find that using spectral methods for binary black hole simulations is over 1,000 times more efficient than much shorter finite-difference simulations of comparable accuracy. The full catalog is publicly available through the sxs Python package and at https://data.black-holes.org .

gr-qc↗

arXiv2025

Modeling the BMS transformation induced by a binary black hole merger

Understanding the characteristics of the remnant black hole formed in a binary black hole merger is crucial for conducting gravitational wave astronomy. Typically, models of remnant black holes provide information about their mass, spin, and kick velocity. However, other information related to the supertranslation symmetries of the BMS group, such as the memory effect, is also important for characterizing the final state of the system. In this work, we build a model of the BMS transformation that maps a binary black hole's inspiral frame to the remnant black hole's canonical rest frame. Training data for this model are created using high-precision numerical relativity simulations of quasi-circular systems with mass ratios $q \le 8$ and spins parallel to the orbital angular momentum with magnitudes $\chi_{1}, \chi_{2} \le 0.8$. We use Gaussian Process Regression to model the BMS transformations over the three-dimensional parameter space $\left(q, \chi_{1}^{z}, \chi_{2}^{z}\right)$. The physics captured by this model is strictly non-perturbative and cannot be obtained from post-Newtonian approximations alone, as it requires knowledge of the strong nonlinear effects that are sourced during the merger. Apart from providing the first model of the supertranslation induced by a binary black hole merger, we also find that the kick velocities predicted using Cauchy-characteristic evolution waveforms are, on average, $\sim5\%$ larger than the ones obtained from extrapolated waveforms. Our work has broad implications for improving gravitational wave models and studying the large-scale impact of memory, such as on the cosmological background. The fits produced in this work are available through the Python package $\texttt{surfinBH}$ under the name $\texttt{NRSur3dq8BMSRemnant}$.

gr-qc↗

arXiv2024

Optimizing post-Newtonian parameters and fixing the BMS frame for numerical-relativity waveform hybridizations

Numerical relativity (NR) simulations of binary black holes provide precise waveforms, but are typically too computationally expensive to produce waveforms with enough orbits to cover the whole frequency band of gravitational-wave observatories. Accordingly, it is important to be able to hybridize NR waveforms with analytic, post-Newtonian (PN) waveforms, which are accurate during the early inspiral phase. We show that to build such hybrids, it is crucial to both fix the Bondi-Metzner-Sachs (BMS) frame of the NR waveforms to match that of PN theory, and optimize over the PN parameters. We test such a hybridization procedure including all spin-weighted spherical harmonic modes with $|m|\leq \ell$ for $\ell\leq 8$, using 29 NR waveforms with mass ratios $q\leq 10$ and spin magnitudes $|\chi_1|, |\chi_2|\leq 0.8$. We find that for spin-aligned systems, the PN and NR waveforms agree very well. The difference is limited by the small nonzero orbital eccentricity of the NR waveforms, or equivalently by the lack of eccentric terms in the PN waveforms. To maintain full accuracy of the simulations, the matching window for spin-aligned systems should be at least 5 orbits long and end at least 15 orbits before merger. For precessing systems, the errors are larger than for spin-aligned cases. The errors are likely limited by the absence of precession-related spin-spin PN terms. Using $10^5\,M$ long NR waveforms, we find that there is no optimal choice of the matching window within this time span, because the hybridization result for precessing cases is always better if using earlier or longer matching windows. We provide the mean orbital frequency of the smallest acceptable matching window as a function of the target error between the PN and NR waveforms and the black hole spins.

gr-qc↗

arXiv2023

Asymmetric eROSITA bubbles as the evidence of a circumgalactic medium wind

The eROSITA bubbles are detected via the instrument with the same name. The northern bubble shows noticeable asymmetric features, including distortion to the west and enhancement in the eastern edge, while the southern counterpart is significantly dimmer. Their origins are debated. Here, we performed hydrodynamic simulations showing that asymmetric eROSITA bubbles favor a dynamic, circumgalactic medium wind model, but disfavor other mechanisms such as a non-axisymmetric halo gas or a tilted nuclear outflow. The wind from the east by north direction in Galactic coordinates blows across the northern halo with a velocity of about 200 km s$^{-1}$, and part of it enters the southern halo. This creates a dynamic halo medium and redistributes both density and metallicity within. This naturally explains the asymmetric bubbles in both the morphology and surface brightness. Our results suggest that our Galaxy is accreting low-abundance circumgalactic medium from one side while providing outflow feedback.

astro-ph.GA↗

arXiv2019

Pattern of lensed chirp gravitational wave signal and its implication on the mass and position of lens

We prose a new measurement strategy of the estimation of the lens mass, as well as the actual amplification, of the lens through the modulation patten of lensed gravitational wave signals alone. This can be done by measuring the frequency and amplitude ratio of peaks and valleys of the modulation pattern of CBC signals, known as "beat", which is a time domain phenomenon of strong lens effect.

gr-qc↗

arXiv2018

The Bending Feature of the Fermi Bubbles: A Presumed Horizontal Galactic Wind and Its Implication on the Bubbles' Age

There are two spectacular structures in our Milky Way: the {\it Fermi} bubbles in gamma-ray observations and the North Polar Spur (NPS) structure in X-ray observations. Because of their morphological similarities, they may share the same origin, i.e., related to the past activity of Galactic center (GC). Besides, those structures show significant bending feature toward the west in Galactic coordinates. This inspires us to consider the possibility that the bending may be caused by a presumed global horizontal galactic wind (HGW) blowing from the east to the west. Under this assumption, we adopt a toy shock expansion model to understand two observational features: (1) the relative thickness of the NPS; (2) the bending of the {\it Fermi} bubbles and NPS. In this model, the contact discontinuity (CD) marks the boundary of the {\it Fermi} bubbles, and the shocked interstellar medium (ISM) marks the NPS X-ray structure. We find that the Mach number of the forward shock in the east is $\sim$ 1.9-2.3, and the velocity of the HGW is ~ 0.7-0.9 $c_{s}$. Depending on the temperature of the pre-shock ISM, the velocity of the expanding NPS in Galactic coordinates is around 180-290 km/s, and the HGW is ~ 110-190 km/s. We argue that, the age of the NPS and the {\it Fermi} bubbles is about 18-34 Myr. This is a novel method, independent of injection theories and radiative mechanisms, for the estimation on the age of the {\it Fermi} bubble/NPS.

astro-ph.GA↗