We can finally see black holes directly but how
How CAN WE SEE BLACK HOLES?
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Many people have asked me: "If black holes trap light, why do we see a ring of light in the photo of the black hole?". The answer is almost simple (making a few simplifications): the black hole is the black circle in the middle; the bright donut you see in the picture is not part of the black hole. Or rather, not yet. It is matter (mainly gas and cosmic dust) that is falling towards it. So, while matter falls into the black hole, it rotates very fast around it, forming a disc and emitting the light that we see as a ring. The brightest part of the disc is the one where the rotating material is directed towards us observers.
At a certain point, however, the matter gets too close to the black hole, overcoming the so-called Horizon of Events (in the photo it is the immaginary line between the light and the dark) and then it is lost forever.
The last very nice thing, however, is that if you notice the black hole is not perfectly circular: it is oval. This shape is not due to an optical effect, but it is due to the fact that in all probability that black hole rotates on itself like a huge, obscure top.