To an astrobiologist: A black hole was once a fiery sun. But then its fire went out. Eventually, it collapsed upon itself, rendering it a mass of tremendous density. And now, a star that once shone brightly holds its light within, even pulling in any surrounding light. In the place of light, a star now creates darkness. A person, too, may end up a black hole. Someone who is meant to shine and teach others—but has burned out and collapsed inward, absorbed in his own self. Now, rather than shining light for others, he absorbs all energy that passes his way...