The effect of host cluster gravitational tidal forces on the internal dynamics of spiral galaxies

New empirical observation by Bidin, Carraro, Mendez \& Smith finds ``a lack of dark matter in the Solar neighborhood" (2012 \emph{ApJ} \textbf{751}, 30). This, and the discovery of a vast polar structure of Milky Way satellites by Pawlowski, Pflamm-Altenburg \& Kroupa (2012 \emph{MNRAS} \textbf{423}, 1109), conflict with the prevailing interpretation of the measured Galactic rotation curve. Simulating the dynamical effects of host cluster tidal forces on galaxy disks reveals radial migration in a spiral structure and an orbital velocity that accelerates with increasing galactocentric radial coordinate. A virtual ``toy model,'' which is based on an Earth-orbiting system of particles and is physically realizable in principle, is available at \textbf{GravitySim.net}. Given the perturbing gravitational effect of the host cluster on a spiral galaxy disk and that a similar effect does not exist for the Solar System, the two systems represent distinct classes of gravitational dynamical systems. The observed `flat' and accelerating rotation curves of spiral galaxies can be attributed to gravitational interaction with the host cluster; no `dark matter halo' is required to explain the observable.