 In order to understand what is going on in and around a black hole, we need to cover the twisting effect of rotating masses on the space surrounding them. The name given to the twisting is frame-dragging. The space is literally dragged along with the rotating mass. The effect was derived in 1918 by physicist Joseph Lenz and Hans Thering. It is known as the Lenz-Thering effect. They predicted that the rotation of a massive object would distort the spacetime metric, making the orbit of a nearby test particle precess like a gyroscope. This does not happen with Newtonian gravity, where the gravitational field of a body depends only on its mass, not on its rotation. It wasn't until 1963 that a mathematician named Roy Kerr discovered the significantly more complicated metric for rotating bodies that made it possible to calculate the precession one can expect from a given mass and rotation of an object like the Earth. To test this effect, NASA developed a satellite called Gravity Probe B and put it into orbit 264 kilometers above the Earth in 2004 where it operated for a year. It used a set of super-sensitive gyroscopes to measure precession due to frame-dragging. It also included a non-gravitational drag identification gyro and compensation micro thrusters to maintain a non-gravitational drag-free environment. It compensated for solar radiation drag and atmospheric disturbances drag. By 2011, data analysis had confirmed that frame-dragging did occur and measured it to within 15% of the amount predicted by the Kerr metric for Einstein's field equations.