Colliding Black Holes

A new type of astronomical observatory came into existence in the past decade and in the past several years has produced amazing results. These are the gravitational wave observatories - LIGO in the United States and VIRGO in Italy. These observatories are looking for and now are frequently finding minute disturbances in space-time. The sources of these disturbances have proven to be the results of collisions and mergers of black holes - a process which propagates shivers in gravity throughout the universe. What is a black hole? How do we know they exist? Where are they? And how are these new observatories finding them? What are NASA’s plans for building a gravitational wave observatory in space?