Deepest note in the universe

The deepest note in the universe is caused by acoustic waves generated by a supermassive black hole in the centre of the Perseus cluster of galaxies, 250 million light years away. The sound, which propagates through the extremely thin gas surrounding the black hole, is a B flat, 57 octaves below middle-C. This is more than a million billion times lower than a human ear can detect. The sound waves are estimated to have been consistently produced by the black hole for around 2.5 billion years.

They were discovered using long-exposure observations by the Chandra X-Ray Observatory, by a team of astronomers led by Professor Andrew Fabian, Cambridge University, Cambridge UK. Their results were announced in Monthly Notices of the Royal Astronomical Society in September 2003