Black holes cannot be studied directly because they do not emit light

However, they can be studied by observing the interactions of objects in their vicinity

Astronomers do this by using x-rays and radio waves to measure the objects near the black hole

Laplace was studying escape velocity when he calculated how large the earth would be if the escape velocity was the speed of light. Thus the idea of the black hole was born.

Black Holes: How is it Studied?