An isolated black hole in empty intergalactic space would be difficult to detect because

Question

Quizplus · Accepted Answer

All of the given options make it difficult to detect an isolated black hole in empty intergalactic space. Gravitational lensing requires a background object whose light is bent by the black hole's gravity, but in empty space, there are no stars behind it to provide that. Black holes cannot emit light from inside their event horizon, so we cannot detect them by observing their radiation. Companion stars usually reveal the presence of a black hole through their orbits and other gravitational effects, but in empty space, there would be no such stars. Finally, X-ray emissions often indicate the presence of black holes, but without matter falling into them to create an accretion disk, such emissions would not occur.

An Isolated Black Hole in Empty Intergalactic Space Would Be