arXiv subjects

LingQin Xue

Publications and source records attributed to LingQin Xue.

4 recordsLinked to original sources

arXiv2026

Recoil-regulated extreme mass-ratio inspirals in AGN disks

Extreme mass-ratio inspirals (EMRIs) are among the primary targets of future space-based gravitational-wave observatories, such as LISA, TianQin, and Taiji. Active galactic nucleus (AGN) disks provide a gas-rich environment in which stellar-mass black holes can migrate toward central supermassive black holes and form EMRIs. Previous studies of this ``wet'' channel have largely neglected stellar interactions within the disk. Here we show that binary formation, hierarchical mergers, and recoil kicks fundamentally regulate wet EMRI formation in AGN disks. Using semi-analytical AGN disk models combined with Monte Carlo simulations across supermassive black hole masses of $10^5$--$10^7M_\odot$ and Eddington ratios of $10^{-3}$-1, we find that recoil kicks from mergers and binary--single interactions repeatedly lift stellar-mass black holes out of the disk plane, temporarily interrupting migration and strongly suppressing EMRI formation in much of parameter space. Detectable EMRIs are therefore preferentially produced in young AGNs, typically within $\sim$ 10-20Myr of disk formation, and often involve merger-grown secondary black holes. We predict LISA detection rates of $\sim$ 1-30yr$^{-1}$, with the observable population dominated by low-mass AGNs and sensitive to the poorly constrained demographics of faint active nuclei. Our results identify stellar interactions as a key ingredient in the evolution of compact objects in AGN disks and show that future EMRI observations can probe both AGN disk physics and the low-mass AGN population.

astro-ph.HE↗

arXiv2025

What Determines the Maximum Mass of AGN-assisted Black Hole Mergers?

The origin of merging binary black holes detected through gravitational waves remains a fundamental question in astrophysics. While stellar evolution imposes an upper mass limit of about 50 solar mass for black holes, some observed mergers--most notably GW190521--involve significantly more massive components, suggesting alternative formation channels. Here we investigate the maximum masses attainable by black hole mergers within active galactic nucleus (AGN) disks. Using a comprehensive semi-analytic model incorporating 27 binary and environmental parameters, we explore the role of AGN disk conditions in shaping the upper end of the black hole mass spectrum. We find that AGN disk lifetime is the dominant factor, with high-mass mergers (>200 solar mass) only possible if disks persist for ~40 Myr. The joint electromagnetic observation of an AGN-assisted merger could therefore lead to a direct measurement of the age of an AGN disk.

astro-ph.HE↗

arXiv2025

Reconstructing the origin of black hole mergers using sparse astrophysical models

The astrophysical origin of binary black hole mergers discovered by LIGO and Virgo remains uncertain. Efforts to reconstruct the processes that lead to mergers typically rely on either astrophysical models with fixed parameters, or continuous analytical models that can be fit to observations. Given the complexity of astrophysical formation mechanisms, these methods typically cannot fully take into account model uncertainties, nor can they fully capture the underlying processes. Here, we present a merger population analysis that can take a discrete set of simulated model distributions as its input to interpret observations. The analysis can take into account multiple formation scenarios as fractional contributors to the total set of observations, and can naturally account for model uncertainties. We apply this technique to investigate the origin of black hole mergers observed by LIGO Virgo. Specifically, we consider a model of AGN assisted black hole merger distributions, exploring a range of AGN parameters along with several {SEVN} population synthesis models that vary in common envelope efficiency parameter ($α$) and metallicity ($Z$). We estimate the posterior distributions for AGN+SEVN models using $87$ BBH detections from the $O1--O3$ observation runs. The inferred total merger rate is $46.2 {Gpc}^{-3} {yr}^{-1}$, with the AGN sub-population contributing $21.2{Gpc}^{-3}{yr}^{-1}$ and the SEVN sub-population contributing $25.0 {Gpc}^{-3} {yr}^{-1}$.

astro-ph.HE↗

arXiv2018

$f(T)$ gravity after GW170817 and GRB170817A

The combined observation of GW170817 and its electromagnetic counterpart GRB170817A reveals that gravitational waves propagate at the speed of light in high precision. We apply the effective field theory approach to investigate the experimental consequences for the theory of $f(T)$ gravity. We find that the speed of gravitational waves within $f(T)$ gravity is exactly equal to the light speed, and hence the constraints from GW170817 and GRB170817A are trivially satisfied. The results are verified through the standard analysis of cosmological perturbations. Nevertheless, by examining the dispersion relation and the frequency of cosmological gravitational waves, we observe a deviation from the results of General Relativity, quantified by a new parameter. Although its value is relatively small in viable $f(T)$ models, its possible future measurement in advancing gravitational-wave astronomy would be the smoking gun of testing this type of modified gravity.

gr-qc↗