 One of the most interesting consequences of general relativity is the structure and impact of a black hole. In the Milky Way segment of the How Far Away Is It? video book, we discussed how they are formed from collapsing massive stars too big for neutron pressure to halt their collapse to a point called a singularity. The Schwartzschild metric showed that if a mass of a body should contract to a small enough radius it could capture light itself. This radius is known as the Schwartzschild radius and forms a sphere known as the event horizon. One of the best illustrations of a black hole was created for the 2015 movie Interstellar with the help of theoretical physicist Kip Thorne. This black hole, called Gargantua, was given a mass of 100 million suns and a super high rotation rate of 99.8% of the speed of light. With this kind of rotation we see that Gargantua is indeed a curr black hole. At 100 million solar masses the Schwartzschild radius is around the distance from the sun to the earth. That's far enough away to make the tidal forces at the horizon quite unnoticeable. We'll use Gargantua to illustrate the properties of general relativity that we have discussed in this segment. So let's build this black hole from the ground up. We are viewing it from the equatorial plane and the object is rotating in on the left and out on the right. Its center is dark out to the Schwartzschild radius. The curr metric shows that light can also be captured in stable orbits outside the event horizon. For a rapidly rotating black hole the orbital volume around the black hole would be significant. This would produce a photon sphere shell encasing the black hole with light from all the stars in the universe accumulated over the entire age of the universe. It would be a sight to see. But given that the light is trapped in orbit we can only see what leaks out. This thin ring around the black hole represents the cross section of this shell we'd see because of light that leaks out in our direction. It is flattened on the left because light rotating with the black hole's rotation can get closer to the horizon than light rotating against the black hole's rotation. Next we see a dense sprinkling of stars with a pattern of concentric shells. This is the pattern produced by the gravitational lensing. Further out we see the dislocation of star positions due to the bending of light by the gravity of the black hole. This black hole has the remnants of an accretion disc that is no longer feeding the black hole. If the disc were not gravitationally lensed the black hole should have looked like this. But because of gravitational lensing the massive amount of light rays emitted from the disc's top face travel up and over the black hole and light rays emitted from the disc's bottom face travel down and under the black hole. This combination gives us the full image of how the black hole would actually look.