The High and Low Notes of the Universe

The Cornell nano-guitar, first built in 1997 but only now played for the first time, twangs at a frequency of 40 megahertz, some 17 octaves (or a factor of 130,000) higher than a normal guitar (see figure). Researchers at Cornell University used laser light to set the 10-micron-long silicon "strings" (actually slender planks of silicon) of the guitar in motion. There is no practical microphone available for picking up the guitar sounds, but the reflected laser light could be computer processed to provide an equivalent acoustic trace at a much lower frequency. The laser light could excite more than one string, creating megahertz "chords." The playing of the nano-guitar will be described by Lidija Sekaric (now at IBM) at the AVS meeting (paper MM-WeM1; 914-945-1802). If the nano-guitar's natural tones are among the most high-pitched sounds in the universe, some of the lowest pitched are to be found in the vicinity of the black hole in the Perseus galaxy cluster. The Chandra x-ray telescope recently saw concentric circles in the inter-galactic gas cloud surrounding the cluster core; some astronomers interpret the ripples as being sound waves (with a frequency some 57 octaves below human hearing, and possibly "the deepest note ever detected from an object in the universe") caused by jets from the black hole shooting outwards into the nearby matter. (see Chandra press release)