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.
In August of 2007 astronomers located a gigantic hole in the universe. This empty space, stretching nearly a billion light-years across, is devoid of any matter. A radical and controversial theory proposes that it is a "Universe-in-mass Black hole"