lowest note in the known universe is the rumbling of a black hole in the Perseus galaxy.
In musical terms, the pitch of the sound generated by the black hole translates into the note of B flat. But, a human would have no chance of hearing this cosmic performance because the note is 57 octaves lower than middle-C. For comparison, a typical piano contains only about seven octaves. At a frequency over a million billion times deeper than the limits of human hearing, this is the deepest note ever detected from an object in the Universe.
