Jongmann Yang

Signatures of field induced spin polarization of neutron star matter in seismic vibrations of paramagnetic neutron star

A macroscopic model of the dissipative magneto-elastic dynamics of viscous spin polarized nuclear matter is discussed in the context of seismic activity of a paramagnetic neutron star. The source of the magnetic field of such a star is attributed to Pauli paramagnetism of baryon matter promoted by a seed magnetic field frozen into the star in the process of gravitational collapse of a massive progenitor. Particular attention is given to the effect of shear viscosity of incompressible stellar material on the timing of non-radial torsional magneto-elastic pulsations of the star triggered by starquakes. By accentuating the fact that this kind of vibration is unique to the seismology of a paramagnetic neutron star we show that the high-frequency modes decay faster than the low-frequency modes. The obtained analytic expressions for the period and relaxation time of this mode, in which the magnetic susceptibility and viscosity enter as input parameters, are then quantified by numerical estimates for these parameters taken from early and current works on transport coefficients of dense matter. It is found that the effect of viscosity is crucial for the lifetime of magneto-torsion vibrations but it does not appreciably affect the periods of this seismic mode which fall in the realm of periods of pulsed emission of soft gamma-ray repeaters and anomalous x-ray pulsars—young super-magnetized neutron stars, radiating, according to the magnetar model, at the expense of the magnetic energy release. Finally, we present arguments that the long periodic pulsed emission of these stars in a quiescent regime of radiation can be interpreted as a manifestation of weakly damped seismic magneto-torsion vibrations exhibiting the field induced spin polarization of baryon matter.

Magnetoelastic pulsations of neutron stars

We discuss non-radial pulsations of a non-rotating neutron star brought to equilibrium in the state of superparamagnetic magnetization of stellar material. High-lighted are equations of magneto-elastodynamics underlying macroscopic description of large-scale motions of magnetically anisotropic neutron matter possessing properties of elastic Fermi-solid. It is shown that incompressible permanently magnetized nuclear matter can transmit perturbations by transverse magnetoelastic waves. The unique feature of oscillatory behavior of superparamagnetic neutron star is its capability of supporting torsional, differentially-rotational magnetoelastic pulsations. Based on the energy variational principle, analytic form is derived for period of non-radial magnetotorsion pulsations triggering Alfvenic hydromagnetic waves in the neutron star magnetosphere. Our order of magnitude estimates for period of this axial, odd parity magnetotorsion mode, referred to as m/t-mode, suggest that magnetoelastic pulsations may affec...

Quasistatic waves of hydrogravity generated in the galactic interstellar medium by a pulsating neutron star

Based on principles of classical hydrodynamics and Newtonian gravity, the theory of hydrogravity, formulated in the manner of hydromagnetic theory, is developed to account for the gravitational effect of global pulsations of a star on the motions of the ambient gas-dust interstellar medium. Analytic derivation of the dispersion relation for canonical gravity waves at the free surface of an incompressible in viscid liquid is presented, illustrating practical usefulness of the proposed approach, heavily relying on the concept of classical gravitational stress introduced long ago by Fock and Chandrasekhar, and accentuating the shear character of this mode. Particular attention is given to gas-dynamical oscillations of a similar physical nature generated by a pulsating neutron star in an unbounded spherical shell of gas and dust promoted by circumstellar gravitational stresses and damped by viscosity of the interstellar matter. Computed in the long-wavelength approximation, the periods of these gravity-driven shear modes, referred to as quasistatic modes of hydrogravity, are found to be proportional to periods of the gravity modes in the neutron star bulk. Given that collective oscillations of cosmic plasma in the wave under consideration should be accompanied by electromagnetic radiation and taking into account that only the radio waves of this radiation can freely travel through the galactic gas-dust clouds, it is conjectured that the considered effect of gravitational coupling between seismic vibrations of a neutron star and fluctuations of the galactic interstellar medium should manifest itself in the radio range of pulsar spectra. Some useful implications of the theory developed here to a number of current problems of asteroseismology are briefly discussed.

Velocities of Magneto-Elastic and Magneto-Electron Waves in Dark Molecular Clouds

We present analytic and numerical estimates for group velocity of wave motions in two models of cold interstellar medium presumably constituting the interior of cores of magnetically supported dark molecular clouds. Namely, in the model of gas-based ferrocolloidal soft matter and in the model of noncompensated electron magnetoplasma. The predictions of these models are given in juxtaposition with data on recent Zeeman measurements of the molecular linewidths detected from dark central regions of star-forming interstellar clouds.

Spiral magneto-electron waves in interstellar gas dynamics

We discuss possible observational consequences resulting from the propagation of transverse magneto-electron waves in the interstellar medium. We briefly describe a magnetohydrodynamic model for the cyclotron waves with emphasis on their analogy with hydrodynamic inertial waves. It is shown that the cyclotron waves are heavily damped in the interstellar medium and, therefore, cannot affect the gas dynamics of star-forming molecular clouds. We developed an analytical model of the helicoidal magneto-electron waves based on the electromagnetic induction equation for the magnetic flux density driven by the Hall and Ohmic components of the electric field generated by flows of thermal electrons. It is established that the helicons can propagate in the interstellar medium without any noticeable attenuation. The presented numerical estimates for the group velocity of the intercloud helicons suggest that spiral circularly polarized magneto-electron waves of this type can be responsible for the broadening of molecular lines detected from dark interstellar clouds.