Black hole (Wikipedia)A black hole is a region of spacetime where gravity is so strong that nothing, including light or other electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of no escape is called the event horizon. Although it has a great effect on the fate and circumstances of an object crossing it, it has no locally detectable features according to general relativity. In many ways, a black hole acts like an ideal black body, as it reflects no light. Moreover, quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is of the order of billionths of a kelvin for stellar black holes, making it essentially impossible to observe directly.
Guards! Guards! (Wikipedia)Guards! Guards! is a fantasy novel by British writer Terry Pratchett, the eighth in the Discworld series, first published in 1989. It is the first novel about the Ankh-Morpork City Watch. The first Discworld point-and-click adventure game borrowed heavily from the plot of Guards! Guards!.
Terry Pratchett (Wikipedia)Sir Terence David John Pratchett OBE (28 April 1948 – 12 March 2015) was an English humourist, satirist, and author of fantasy novels, especially comical works. He is best known for his Discworld series of 41 novels.