Question

why do astronomers have difficulty locating black holes and use observations of stars to detect their presence? they do not give off light. they give off too much light. they are invisible. there is too much gas

Explanation:

Black - holes are regions of space with extremely strong gravitational fields. Light cannot escape from them, so they do not emit light. Astronomers detect their presence through the gravitational effects on nearby stars.

Answer:

They do not give off light.