Effect of a tide on the Parker-Jeans instability

By performing a linear stability analysis in the presence of an external tidal field, we have obtained a generalized dispersion relation for the Parker-Jeans instability. We have found that a compressive tidal field helps in initiating the collapse of the interstellar cloud towards star formation. This effect is present even when the Jeans mass is more than the mass of the system under consideration. In such cases, of course, it is the magnetic field that makes the compressive tidal force effective via the Parker instability. We argue that this effect can be of importance in overcoming the disrupting effect of a random magnetic field.