Current-sheet Evolution near a Hyperbolic Magnetic Neutral Line in Hall Magnetohydrodynamics: An Exact Solution

\large{\bf Abstract-} Unsteady Hall Magnetohydrodynamics (MHD) near a hyperbolic magnetic neutral line is investigated. An exact analytical solution describing a self-similar evolution is given. This solution shows a negligible impact on the current-sheet formation process near the hyperbolic magnetic neutral line at small times by the Hall effect but, subsequently, a quenching by the Hall effect of the finite-time singularity exhibited in ideal MHD and, hence a prevention of the current density blow-up at large times. The asymptotic result given by this time-dependent solution is in full quantitative agreement with the formulation of \textit{steady} Hall MHD near a $X$-type magnetic neutral line (Shivamoggi [23]). The latter formulation showed that this asymptotic result indeed corresponds to a hyperbolic configuration of the magnetic field lines in the \textit{steady} case.