Free Astronomy Magazine July-August 2020

JULY-AUGUST 2020 T here are at least 2,000 billion galaxies in the observable universe, each of which contains, on average, many bil- lions of stars. Many of these billions of stars are assumed to host planets. This means that, already in the region of the universe closest to us (where the cosmological red- shift, z, is near or at zero), there are proba- bly trillions of planets, and we can expect that a small fraction of them (millions) are very similar to Earth and therefore are hab- I s life more typical in elliptical or spi- ral galaxies? In the background, two worthy representa- tives of those cate- gories: M60 (in the center) and NGC 4647 (top right). [NASA, ESA and the Hubble Heritage (STScI/AURA)] itable by terrestrial life forms. Depending on how hospitable a planet might be, life could evolve to develop technological species, those which by definition are “biological species that have developed electronic de- vices and are capable of significantly influ- encing their planetary environment.” In order for an intelligent species to have the time necessary to evolve up to a tech- nological level, it is necessary that the host star resides in the main sequence for billions