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

Abstract

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.