Strange but True: Black Holes Sing

Authough sound cannot be heard in space ,it can some times be seen.

In the dark heart of the Perseus galaxy cluster, 300 million light -years from earth,a supermassie black hole has been singing the same note for 2.5 billion years.Its tone registers 57 octaes below middle C and according to scientists at NASA's Chandra X-Ray Center, is a resounding B-flat.YEt ,how is this possible in the vacuum of space?

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