Destruction of the central black hole gas reservoir through head-on galaxy collisions

A massive black hole exists in almost every galaxy. They occasionally radiate a vast amount of light by releasing gravitational energy accreting gas, with cumulative active period only few $10^8$ years, so-called the duty cycle Active Galactic Nuclei. Namely, many galaxies today host starving hole. Although galaxy collisions have been thought to enhance nucleus activity, origin cycle, especially shutdown process, is still critical issue. Here we show that are also capable suppressing fueling using an analytic model and three-dimensional hydrodynamic simulations, applying well-determined parameter sets for galactic collision Andromeda Our models demonstrate central can strip torus-shaped gas surrounding hole, putative source. The derived condition switching-off indicates significant fraction currently bright nuclei become inactive, reminiscent fading/dying phenomena associated merging events. Galaxy may therefore be responsible both turning-on depending on orbit (head-on or far-off-centre).