Flexi Says: Black holes lose energy and mass very slowly over time by a process called Hawking radiation. Throughout space, particle and anti-particle pairs continually pop into and out of existence. One of these particles has positive energy and the other has negative energy. Most often, the two particles recombine and cancel out, disappearing back into the vacuum of space. However, as this occurs around the edges of black holes, the particle of negative energy can fall into the black hole while the particle with positive energy remains outside. Adding a negative energy particle to the black hole removes mass from the black hole in accordance with E=mc2. When the black hole loses enough mass, it can no longer prevent energy and mass from escaping. The black hole sheds its remaining light and energy all at once in a huge flash that moves away on either side, forming a feature known as a light echo.