Even if a black hole emitted no light, we can still detect it:
A) from sound waves produced by material falling onto the black hole
B) by tides produced on the Earth's oceans
C) through its Hawking radiation
D) through its gravitational effect on surrounding gas or stars
E) by looking for dark patches on the sky where the black hole swallows background light

Question

Quizplus · Accepted Answer

We can detect black holes through their gravitational effect on surrounding gas or stars. As material falls towards the black hole and spirals in, it heats up and emits radiation which we can observe. Additionally, the strong gravitational forces of a black hole can cause nearby stars to orbit around it in unusual ways, giving us indirect evidence of its presence.

Even If a Black Hole Emitted No Light, We Can