Answer:
Large spherical regions from which no light is detected
Step-by-step explanation:
A black hole is an object that has an extremely high density such that it possesses very powerful gravitational force that prevents the escape of all objects including light from it, and consumes nearby objects.
Due to the power of the gravitational force of a black hole, at the center, objects are infinitesimally compressed resulting in the inapplicability of the concept of space and time and the location is known as a singularity
Therefore, the search for black holes involves searching for large spherical regions from which no light is detected.