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PA & G. Lipunova "Simulating the shock dynamics of a neutron star accretion column"
Numerical one-dimensional study of the dynamics of an accretion column, reproducing the classic Basko-Sunyaev's solution, predicting a fundamental applicability limit for the mass accretion rate and an oscillation mode related to the vertical motions of the matter.
The figure shows variations of the local normalised radiation flux during the settling stage.
PA & O. Bromberg. "Interface instabilities in hydrodynamic relativistic jets"
3D special-relativistic study of Rayleigh-Taylor and Richtmyer-Meshkov instabilities in a steady-state relativistic jet. To reach the steady-state, we used a novel 'dynamic cocoon' approach: the ambient medium is moving in the same direction as the jet.
The picture shows cross-sections of the relativistic Bernoulli parameter, see the paper for details.
PA & A. Biryukov 2021 "Magnetic angle evolution in accreting neutron stars"
Analytic study of the equilibrium surfaces in the bead-on-a-wire motions inside a rotating dipolar magnetospheres.
The videos show how the surface change with changing magnetic angle (left) and how it looks like when viewed from different perspectives.
A. Biryukov & PA 2021 "Magnetic angle evolution in accreting neutron stars"
A unique study of the effect of accretion and spin-up in a binary system on the magnetic obliquity of a neutron star. The picture shows the evolution of the spin, its inclination with respect to the spin-up torque α, and magnetic angle χ.
PA & J. Poutanen 2021 "Mechanical model of a boundary layer for the parallel tracks of kilohertz quasi-periodic oscillations in accreting neutron stars"
A study that reproduces the "parallel-tracks" effect observed for kHz QPOs with a simple accretion boundary layer model.
The picture shows how the frequency and instantaneous luminosity of the boundary layer change with time (the time is colour-coded). Frequency and flux are correlated on short time scales, but the parameters of the correlation change with time, that produces the "parallel tracks" effect.
PA, J. Nättilä, J. Poutanen 2020 "Kilohertz quasi-periodic oscillations from neutron star spreading layers"
Numerical study of the spreading layer on the surface of an accreting non-magnetised neutron star. One of the results is a double inertial mode suspiciously similar to kHz QPOs in low-mass X-ray binaries.
The pictures show a quasi-3D representation of the spreading layer (to the left: the surface represents the vertical scale height of the layer, and the colour shows its effective temperature) and four stages of the evolution of the layer, including development of shear instabilities and excitation of the inertial modes.
Rusakov, PA, and Bromberg 2025 "Numerical approach to compressible shallow-water dynamics of neutron-star spreading layers"
A more advanced numerical approach to the spreading layer dynamics, using an irregular-grid code SPLASH developed by Alexandr Rusakov. The pictures show a surface density and velocity maps (left) and simulated dynamic power-density spectra, compared to different characteristic frequencies of the system. Depending on the viewing angle, different frequency peaks dominate the spectra.
PA, Bromberg, Levinson, and Nakar 2025 "Tidal disruption of a magnetized star"
Numerical study making use of Athena++, aimed on connecting the initial magnetic fields embedded in a star with the fields that develop during the fallback and accretion disc formation.
The main amplification site for the field is the system of nozzle shocks near the pericentre of the initial orbit. Shocks cause turbulence, and turbulence amplifies the fields through the kinematic dynamo mechanism.
The pictures above show 3D-renderings of the field lines during the disruption (2.5 days after the initial flyby) and during the formation of the disc (65 days after). On the right is a link to an animation of density evolution in the equatorial plane.
Biryukov, PA, and Levinson 2025 "Rotational evolution of deformed magnetized neutron stars: implications for obliquity distribution and braking indices statistics"
A deep dive into rotation of deformed neutron stars involved in free precession and spun down by pulsar losses. Even tiny deformation creates a variety of complicated evolutionary paths, thus broadening the distribution in magnetic angles. Free precession has the potential of modulating magnetic angles on the time scales much shorter than the characteristic times, but longer than the observational time spans. Some observational properties of radiopulsars, most importantly their braking indices, are neatly explained by a population of deformed, effectively rigid-body, neutron stars.
The picture shows two sample evolutionary tracks of the rotational axis in the reference frame of the stellar crust. The only difference between the two curves is in the initial orientation of the rotation axis, which leads to a drastically different track and a different final value of the magnetic angle.
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