HOW ARE 'BLACK HOLES' DETECTED?

Black holes do not emit light; in fact, they completely absorb and trap light that is close to them. If this is the case, how can we possibly observe or detect them? 

As it tuns out, while black holes do not emit light or any matter , the effects of black holes can be detected. As matter is pulled into the black hole, it accelerates and heats up. When the temperature of the matter increases, atoms are ionised. Once these atoms reach temperatures of a few million Kelvin, the X-rays that are emitted can be detected and observed by scientists. While there are other possible X-ray sources in the universe - other than black holes- black holes have fluctuating X-ray emission intensity since matter is not pulled inside at a uniform, constant rate. The second way scientists detect black holes is by observing their gravitational influence. For example, at the centre of our galaxy-Milky Way- we see an empty spot where all the stars are circling around as if they are orbiting a really dense, dark mass That's where the black hole is located.