Objects roll quickly towards it as they approach the steep slope. A neutron star creates a dent with very steep sides. Objects rolling in reach half the speed of light. A Black Hole makes such a deep dent, that it forms a well. The sides of this gravitational well are so steep that even light can not escape.
Light rays approaching a black hole are bent around by steeply curved space.
Rays that come closer may go into orbit around the black hole. Light that comes dangerously close to the black hole is inevitably drawn in. Once inside the event horizon, light spirals down the steep sides of the gravitational well. A black hole acts as a gravitational lens when it comes between an object and an observer. With perfect alignment the image right becomes a ring known as an Einstein Ring.