Hao-Jui Kuan 官顥叡

Tidal resonances and premerger transients

During inspiral the orbital frequency sweeps through a neutron star's oscillation spectrum, and resonant excitation of g-, f-, and shear modes can stress the crust to failure, redistribute angular momentum, and amplify the magnetic field. I developed the general-relativistic framework for these resonances and use precursor flare timings — including quasi-periodic features observed in short gamma-ray burst precursors — to perform asteroseismology on the flaring star, constraining its spin and the nuclear equation of state.

Recent nonlinear simulations further reveal mode-driven differential rotation, parametric instability, and spin-up, strengthening the case for premerger magnetic amplification.

Precision waveforms in numerical relativity

Numerical accuracy is part of the physics: a waveform cannot reveal a subtle tide or a modification of gravity unless its error budget is smaller than the effect. I quantify uncertainties from grid resolution, wave extraction, initial-data solver, and evolution code in binary neutron star simulations, and use fully relativistic evolutions of tidal resonance to test where linear-response descriptions of the dynamical tide cease to hold. Residuals against analytic approximants then become diagnostics of missing physics rather than of numerical noise.

Strong-field gravity and scalarization

Dynamical compact stars probe gravity in regimes inaccessible to weak-field experiments. I study scalarization and descalarization in massive scalar-tensor and scalar-Gauss-Bonnet theories: their formation through core collapse and accretion, their nonlinear stability and nonuniqueness, and their imprint on quasiequilibrium binaries, merger waveforms, and postmerger remnants. Because a scalar field and an uncertain equation of state can shift the same observables, I emphasize combining inspiral, collapse threshold, and postmerger spectrum over any single anomalous frequency.

Dense matter, structure, and stability

The equation of state enters as a set of measurable consequences rather than a label: composition gradients set buoyancy and the g-mode spectrum, elasticity determines whether motion penetrates or fractures the crust, tidal deformability shapes the inspiral, and thermal pressure and differential rotation govern whether a massive remnant survives. I follow these observables through a common stellar model so that degeneracies with spin, temperature, magnetic field, and the underlying theory of gravity can be cross-checked rather than assumed away.