Galactic Black Holes and Other Mysteries

In tonight's sleepy story, we take a look at three scientific topics that retain a part of the mystery: - The existence of supermassive black holes at the center of galaxies, that are several million times more massive than "regular" black holes born from supernovas. Did these gigantic black holes appear as such, did they become so big by absorbing other bodies for billions of years, or is it something else? - Deep-sea gigantism, the fact that many species living deep underwater become much bigger than their shallow waters relatives, despite living in an environment that offers much less food. - The climate on Venus: was it always as harsh, or did this planet once look more like Earth before its atmosphere shifted dramatically?