The Study of Astrophysical Magnetized Flows

Abstract

A detailed study of magnetized astrophysical ows has been carried out in the magnetohydrodynamic and special relativistic magneto- hydrodynamic regime. We have considered the thermodynamics of the ow to be described with a xed as well as, a variable adiabatic index equation of state (EoS). As examples of MHD ow, we have studied (i) funnel accretion onto neutron stars and white dwarfs, (ii) magnetized equatorial out ows from around a compact magne- tized star, and (iii) magnetized relativistic out ows about the axis of symmetry from compact objects like black holes. Possibly for the rst time, we obtained semi-analytical magnetized accretion solutions onto compact objects with a hard surfaces such as neutron stars which satis es the inner boundary condition, where the accreting matter gently settles onto the surface of the star. We also compared these solutions in Newtonian & pseudo-Newtonian regime. We assumed that neutron star has a strong dipole magnetic eld whose dipole moment is aligned along the rotation axis of the star. We have included cooling processes like bremsstrahlung and cy- clotron. Depending on the Bernoulli parameter of the ow and the rotation period of the star, we obtain various solutions which may possess a single sonic point or multiple sonic points. We have also studied the dependence of accretion solutions on plasma composi- tions. All types of accretion solutions undergo a very strong primary shock which forms near the star surface. The strength of the pri- mary shock increases with the rotation period of the star, but the shock location is weakly dependent on the period. Due to the pres- ence of multiple sonic points, we can nd a secondary shock within a very small region of the parameter space but this shock is weak and the shock location, the shock strength, and the compression ra- tio depends signi cantly on the rotation period of the star and the total energy of the ow. We also calculate the total luminosity of the magnetized accretion solution which is in good agreement with observations. We have also studied a case of white dwarf where our results match with the observations. We have found that cyclotron cooling and bremsstrahlung cooling are necessary to obtain a consis- tent accretion solution i.e., a solution which connects the ow from the accretion disk to the star surface. We studied the e ect of plasma composition on the equatorial wind out ow with variable adiabatic index EoS. We have found that ter- minal velocity depends upon the plasma composition. Lepton domi- nated winds with higher values of Bernoulli parameter have high ter- minal speeds. We have also studied solutions for di erent energies, angular momenta and in di erent gravity i.e., Newtonian & pseudo- Newtonian potential. For the same values of the Bernoulli parameter (energy) and the total angular momentum, a wind in strong gravity is more accelerated, compared to wind in Newtonian gravity. We showed that ow variables like the radial, azimuthal velocity compo- nents, temperature, etc all depend on the composition of the ow. We continue our out ow study in case of collimated out ows or jets in special relativistic magnetohydrodynamic regime with vari- able adiabatic index EoS. We found that plasma composition mainly a ects the velocity and the temperature of the jet but the collimation of jet and fast critical point location appears to have no dependence on plasma composition. We explore all out ow solutions and found that the solution depends on the current distribution parameter, the magnetization parameter, the inclination angle of eld lines with re- spect to the disk plane, and Alfv en point radius. Fast point location can be related to collimation shock location because the super-fast

ow is causally disconnected from the ow which is behind.