Neutron stars are the densest objects without event horizons. Their interiors compress nuclear matter well beyond the densities reached in atomic nuclei, and their gravitational fields are strong enough that general relativity is the minimum theoretical commitment required to describe them. I use that extremity as leverage. Most of my work lives in two connected areas.

Neutron-star physics

Understanding what dense matter does inside a neutron star and how that physics imprints itself on signals we can measure. I alternate between analytical modelling (stellar-structure equations, relativistic linear perturbation theory for oscillation modes, elastic-crust formalism) and 3D numerical-relativity simulations of binary mergers with the Computational Relativistic Astrophysics group at AEI. For observational questions I work with pulsar timing data and with hierarchical Bayesian methods for population-level inference from gravitational-wave catalogs.

• Binary mergers and post-merger remnants. Hypermassive remnants are hot, differentially rotating, and right on the edge of collapse. I study their hydrodynamical and thermal structure and how that shapes the postmerger gravitational-wave signal, using full numerical relativity across a range of equations of state. Companion simulation movies live on the convection page.
• Oscillation modes and tidal resonances. A neutron star’s equation of state controls the spectrum of modes its interior can support. I characterise those modes for stratified stars with solid crusts, study how resonant and non-resonant tidal excitation deposits energy into the crust, and ask when the resulting elastic strain can break the crust and seed electromagnetic precursors. The crust-strain page has animations of this process.
• Universal relations for neutron stars. EOS-insensitive relations among bulk neutron-star quantities let one cancel the equation-of-state dependence of one observable against another. I derive such relations and work out when they hold or break.
• Pulsars, magnetars, and precession. The complementary electromagnetic view: spin-down, free precession, and polarisation modulations trace a neutron star’s shape, elasticity, and magnetic geometry, and occasionally reveal features (like a freely precessing magnetar) that directly constrain interior physics.
• Exotic compact-object models. What if some of the “neutron stars” we observe aren’t ordinary neutron stars? Quark-star and strangeon-star models remain viable within current constraints and predict subtly different mass–radius relations, oscillation spectra, and gravitational-wave signatures.

Tests of strong-field gravity

Using compact objects as laboratories to look for departures from general relativity that are invisible in the weak-field regime. Depending on the theory, the work involves deriving modified stellar-structure and perturbation equations, computing the resulting post-Newtonian waveform corrections, or propagating them through full numerical-relativity simulations. Observational constraints come from X-ray pulsar pulse profiles and from gravitational-wave catalogs.

• Scalarised neutron stars in modified gravity. Above a critical compactness, neutron stars in scalar-tensor and scalar-Gauss-Bonnet theories pick up a non-trivial scalar field that changes their structure, tidal deformability, and pulse-profile appearance.
• Beyond-GR waveform corrections. Additional propagating degrees of freedom produce dipole radiation on top of GR’s quadrupole and modify the inspiral phasing. Full numerical-relativity simulations of mergers in modified gravity also give access to universal relations that survive beyond GR.
• Lorentz-violation signatures. Minimal Standard-Model-Extension coefficients alter how a rotating, deformed neutron star precesses — and therefore the continuous gravitational-wave spectrum and pulsar-timing signatures it leaves behind.

The publications page has the full chronological list. The convection and crust-strain pages host the numerical-simulation and mode-excitation animations that accompany two recent papers.