Thu December 29, 2011 By:

how are black holes detected. They don't emit light and so spectroscopy can't be used. Then how are they detected.

Expert Reply
Thu December 29, 2011
Black holes are detected as surrounding material (like gas) is funnelled by the force of gravity into a disc around the black hole. The gas molecules in the disc swirl around the black hole so fast that they heat up and emit X-rays. These X-rays can be detected from Earth.
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