The lowest note in the universe is coming from a black hole in the Perseus Cluster, about two hundred fifty million light years away.
What's happening out there is that intergalactic gas has concentrated around a cluster of galaxies, forming a cloud. A massive black hole is sending out jets of particles that crash into the cloud, causing pressure waves to ripple outward.
Some astronomers interpret these as sound waves. Of course, even if you call it sound, it's too low for anyone to hear. They estimate the note to be a "B flat," about fifty-seven octaves lower than middle C.
Researchers now think that many black holes may produce such waves, which can affect the way galaxies, and even galaxy clusters, behave.