Super Massive Black Holes by PHD Comics. Sagittarius A*, the super massive black hole at the center of the Milky Way, has a mass million times the mass of our sun, and a diameter equal to the distance between the sun and Mercury.
The age of the universe and its vast number of stars suggests that extraterrestrial life should be common. If that’s the case, then where is everyone? In this infographic we explore some possibilities.