Mass accretion by the nuclei of disk galaxies, II

Abstract

Repeated explosions in the nuclei of galaxies are now accepted as observationally established phenomena. Each explosion leads to the ejection of gas from the central region of a galaxy with velocities depending on the strength of the explosive event. In the process the nucleus temporarily becomes gas-deficient. It is suggested that the mass los is replenished by the accretion of the mass which is shed by those evolved stars in the galactic bulge that possess relatively low rotational velocities. The gas to be accreted is assumed to be magnetized. In the present model, the accretion rate has been assumed to be a function of both radial distance and time. The cross-radial equation of motion has been solved to derive the expression for the rotational velocity which is found to bealmost linear with the radial distance from the centre. The radial equation has been solved to calculate the time-scale over which the nucleus accumulates sufficient mass to undergo instability and suffer explosion. The calculated time-scale range from few multiples of 10⁷ to a few multiples of 10⁸ yr. This range agrees very well with that as has been suggested on the basis of observation in the case of our own Galaxy.