What exactly are black holes? A black hole is a region of space with a gravitational pull so powerful that nothing can escape from it, not even light. The visualization simulates the appearance of a black hole where infalling matter has collected into a thin, hot structure called an accretion disk. Credit: Event Horizon Telescope Collaboration How do black holes develop? A large star collapsing in on itself creates a region of space with a very high gravitational pull, which is how black holes are created. Artist's conception depicting the growth channels of black holes in the nearby and distant universe. In the nearby universe, smaller black holes grow by accretion while larger black holes grow by mergers. In the distant universe, the opposite is true. Credit: M. Weiss How large can black holes grow? Black holes can be as big as billions of times the mass of the Sun or just a few times it. Black holes are some of the most fascinating objects in space. (Image credit: solarseven vi...