Eerie Howls from Dunes, Black Holes
Marco Polo once described the roar of sand dunes as the call of desert spirits who "at times fill the air with the sounds of all kinds of musical instruments." Thanks to some new research, now we know why. At the same time, astronomers using extra-sensitive ears have discovered an enormous black hole, 250 million light years away, that's humming the lowest note ever heard -- a B-flat, 57 octaves below middle C.

The September 2003 issue of Discover reports that researchers Stephane Douady and Bruno Andreotti accidentally triggered a sand avalanche and were captivated by the strange rumble it created. So they carted 160 pounds of Moroccan sand back to their Paris laboratory to investigate further.

It turns out that when sand moves, expanding and contracting air holes create sound waves. Random movements create waves that tend to cancel each other out, but a flow in unison -- such as an avalanche -- creates distinct musical tones. The scientists are still puzzled by why so many grains tend to move in such a synchronized manner when they fall.

According to a September update from the journal Nature, it is these jets that are creating the deep sound -- bubbles of gas that oscillate and ripple with a wavelength of 36,000 light years. (Discover reports that it would take a piano almost 50 feet long to create such a low note; we suspect that it would have to be much bigger.) The energy equivalent of 100 million supernovas -- exploding stars -- is being used to create these massive bubbles of gas, and the black hole has been doing this for quite a while. In a September 16, 2003 New York Times article, Dr. Andrew Fabian of Cambridge University remarked, "It's the longest-lasting symphony we know of."

Read about the musical dunes in Discover magazine

Find out more about the black hole sound from NASA's web site, a NASA news release, or from the journal Nature