Astronomers say they have heard the sound of a black hole singing. And what it is singing, and perhaps has been singing for more than two billion years, they say, is B flat —a B flat 57 octaves lower than middle C.
The ''notes'' appear as pressure waves roiling and spreading as a result of outbursts from a supermassive black hole through a hot thin gas that fills the Perseus cluster of galaxies, 250 million light-years distant. They are 30,000 light-years across and have a period of oscillation of 10 million years. By comparison, the deepest, lowest notes that humans can hear have a period of about one-twentieth of a second.
The black hole is playing ''the lowest note in the universe,'' said Dr. Andrew Fabian, an X-ray astronomer at the Institute for Astronomy at Cambridge University in England.
https://www.nytimes.com/2003/09/16/science/music-of-the-heavens-turns-out-to-sound-a-lot-like-a-b-flat.html
