Scientists believe black holes exist according to evidence as determined by Einstein’s Theory of Relativity. Experts use Einstein’s understanding of gravity to determine the immense gravitational pull of a black hole. In this image, information from the Chandra X-ray Observatory is combined with images from the Hubble Space Telescope. NASA believes these two black holes are spiraling toward each other and have been doing so for 30 years. NASA thinks they will eventually become one big black hole.