  The Fermi paradox has given rise to various attempts to explain why no
evidence of extraterrestrial civilisations was found so far on Earth and in our
Solar System. Here, we present a dynamical model for the development of such
civilisations, which accounts for self-destruction, colonisation and
astrophysical destruction mechanisms of civilisations including gamma-ray
bursts, type Ia and type II supernovae as well as radiation from the
supermassive black hole. We adopt conservative estimates regarding the
efficiency of such processes and find that astrophysical effects can influence
the development of intelligent civilisations and change the number of systems
with such civilisations by roughly a factor of 2; potentially more if the
feedback is enhanced. Our results show that non-equilibrium evolution allows
for solutions in-between extreme cases such as "rare Earth" or extreme
colonisation, including scenarios with civilisation fractions between 10^{-2}
and 10^{-7}. These would imply still potentially large distances to the next
such civilisations, particularly when persistence phenomena are being
considered. As previous studies, we confirm that the main uncertainties are due
to the lifetime of civilisations as well as the assumed rate of colonisation.
For SETI-like studies, we believe that unbiased searches are needed considering
both the possibilities that the next civilisations are nearby or potentially
very far away.
