Astronomers have identified and measured the most massive black hole to date, which tops out at a mass of 36 billion solar masses. This ultramassive black hole is close to the theoretical upper limit of what is possible in the Universe and is roughly 10,000 times heavier than Sagittarius A*, a supermassive black hole at Milky Way’s center. This Hubble image shows the Cosmic Horseshoe gravitational lens (to the right from the center): the newly-discovered...