An artist's illustration of the longest black hole jet system ever observed. Nicknamed Porphyrion after a mythological Greek giant, these jets span roughly 7 megaparsecs, or 23 million light- years. That is equivalent to lining up 140 Milky Way galaxies back-to-back. Credit: E. Wernquist / D. Nelson (IllustrisTNG Collaboration) / M. Oei

Astronomers have observed three types of black holes in the universe. Stellar-mass black holes formed from the collapse of a massive star, intermediate mass black holes found in some star clusters, and supermassive black holes that lurk in the centers of galaxies.