Binary Black Hole Collisions
Grazing Black Holes
These images, produced in 1999, represent an important intermediate step in the development of numerical simulations of black hole collisions. Prior to that time, the only detailed simulations available were of direct head-on collisions an especially simple situation. Yet astrophysical black holes are expected to orbit each other before they collide as they orbit, the system emits energy in the form of gravitational waves, which leads to the or bit becoming ever closer and faster, until finally the black holes merge within a few milliseconds to form a single larger black hole. The merger releases a formidable burst of gravitational waves. While this simulation did no t follow orbiting black holes, it was the first to simulate a more realistic grazing collision. Since head-on collisions are axisymmetric and, as such, can be described with a mere two space variables, this was the first det ailed three-dimensional simulation of a black hole collision. It is an inevitable problem of such simulations that they become unstable and break down after a certain time has elapsed this is due to the extreme changes in th e gravitational field inside the black hole. The simulation shows the apparent horizons the boundary (at a given time of the evolution) separating the outside world from the inside of the black hole, from which no light can escape to the outside. The horizons can be se en as bubble-like surfaces in the center of the simulation; the different colours indicate surface patches of various curvature. The gravitational waves are represented by different colours for different intensities.
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