Active Galactic Nuclei: Boon or Bane for Biota?
  Active Galactic Nuclei (AGNs) emit substantial fluxes of high-energy
electromagnetic radiation, and have therefore attracted some recent attention
for their negative impact on galactic habitability. In this paper, we propose
that AGNs may also engender the following beneficial effects: (i) prebiotic
synthesis of biomolecular building blocks mediated by ultraviolet (UV)
radiation, and (ii) powering photosynthesis on certain free-floating planets
and moons. We also reassess the harmful biological impact of UV radiation
originating from AGNs, and find that their significance could have been
overestimated. Our calculations suggest that neither the positive nor negative
ramifications stemming from a hypothetical AGN in the Milky Way are likely to
affect putative biospheres in most of our Galaxy. On the other hand, we find
that a sizable fraction of all planetary systems in galaxies with either
disproportionately massive black holes ($\sim 10^{9-10}\,M_\odot$) or high
stellar densities (e.g., compact dwarf galaxies) might be susceptible to both
the beneficial and detrimental consequences of AGNs, with the former
potentially encompassing a greater spatial extent than the latter.
