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How Do You Know That a Black Hole is a Black Hole?

-- Eileen Kennedy | October 28, 2019

EHT image of event horizon in the central supermassive black hole of M87

Question:

How do you know that you are looking at a black hole through a telescope? I think these photos looks like eclipses. How do you know it is a black hole?.

-- Eileen Kennedy

Answer:

Black holes give us clues as to there existence by how they influence the motions of other objects, such as stars and gas, that happen to be near a black hole. For example, stars that pass near a black hole have their motions bent in such a way as to tell us that there must be a very large mass that is pulling on the star. Since we see no light coming from the region of the mass which perturbed the star’s motion, we know that it must be a black hole. We can also see black holes by how they capture gas and dust from stars that are near a black hole. When gas and dust is drawn into a black hole it gets heated to very high temperatures, which causes it to glow. The properties of that glowing gas also give us strong clues as to the presence of a black hole.

-- Jeff Mangum

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