A black hole is a region of space-time, the gravitational attraction of which is so great that they cannot even leave it.
Objects moving with the Speed of Light, including quanta of the light itself. The boundary of this area is called the event horizon, and its characteristic size is called the gravitational radius. In the simplest case of a spherically symmetric black hole, it is equal to the Schwarzschild radius.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.