Free Astronomy Magazine July-August 2020

43 JULY-AUGUST 2020 ASTROBIOLOGY so-called “principle of mediocrity.” According to this principle, if an element is randomly extracted from a well-defined category of elements, it is very likely that it is representative of the whole category. Ap- plied to astronomy, the principle of mediocrity tells us that there are no privi- leged realities in the uni- verse and, in the absence of contrary evidence, the evolution of our solar sys- tem, our planet, and all life on it have to each be con- sidered typical scenarios of the reference classes to which they belong. An example will clarify the concept. Three famous as- tronomers of the past, James Gregory, Isaac New- ton and Christiaan Huygens (also known for the optical schemes they each gave N GC 5128, in the constellation Centaur, is an inter- mediate class be- tween ellipticals and spirals. The photo above, taken in visi- ble light with the 2.2-meter MPG/ESO telescope at La Silla Observatory, does not show the violent activity of the SMBH evident in other wavelengths (right). [ESO/WFI (Optical); MPIfR/ESO/APEX/ A.Weiss et al. (Submillimetre); NASA/CXC/CfA/R. Kraft et al. (X-ray)] lar medium with metals. The latter would favor the formation of planets, while the shortage (or absence) of supernovae would preserve any life forms present on those planets from being cut down by the radiation re- leased in the explosions. The surprising results reached by Dayal’s team have obviously been the subject of discussion among astronomers, and just recently their hypoth- esis has regained the lime- light thanks to a critical reworking based on the