Material that falls into a black hole can be seen by the electromagnetic radiation it emits before it reaches the event horizon.

Question

Quizplus · Accepted Answer

This is known as the "last gasp" or "final fireworks" of matter as it is pulled into a black hole. The intense gravitational forces generate high-energy radiation, including X-rays, which can be detected by scientists observing telescopes outside the black hole's event horizon. However, once the material passes the event horizon, it is no longer visible as it is trapped within the black hole's singularity.

Material That Falls into a Black Hole Can Be Seen