Hi Aditi,

actually, we can detect meteors without seeing them by satellites and atmosphere alerts that detect if a meteor even if hours away from the earth are coming our way. And so Black holes are detected as surrounding material (like gas) is funneled by the force of gravity into a disk around the black hole. The gas molecules in the disk swirl around the black hole so fast that they heat up and emit X-rays. These X-rays can be detected from Earth. 

Hope you understand and if you have any further points that you'll like to add, feel free to do so.