Right now, there is a piece of NASA equipment called the Laser Interferometer Space Antenna (LISA) hurtling out in space, designed to detect the gravitational waves that result when large, stellar-mass black holes or neutron star binaries smash into one another. LISA is a complimentary instrument built to work with the ground-based Laser Interferometer Gravitational Wave Observatory (LIGO); whereas LIGO can listen to gravitational waves that are between the frequencies of 10 and 1000 Hertz (very close to the human ear’s capabilities), LISA is able to pick up the quietness of space, listening to frequencies between 0.03 milliHertz and 1 Hertz. If the floating receiver can detect gravitational waves, it would be the first direct proof of Einstein’s theory of relativity.
Craig Hogan, a researcher on the LISA project, told Nature that “so far we’ve turned snapshots of the universe into a silent movie. Detecting gravitational waves would be like adding a soundtrack—and that is potentially much more transformative to science as a whole than discovering dark energy.” Against all previous assumptions, it turns out that the universe is not silent and sound waves (of sorts) do travel along gravitational waves.
In this instance, astrophysics is not a visual discipline, but an aural one. We cannot see black holes—even ones the size of a million solar masses—but we can “listen” to the sound-like vibrations in space-time that occur when these stellar and galactic events occur.
Black Hole 1 A 10 solar mass black hole with an initially circular orbit slowly spirals into a million solar mass black hole
Black Hole 2 A 10 solar mass black hole with a highly eccentric orbit rapidly spirals into a million solar mass black hole.
Here on Earth, similar natural radio waves can be heard in the form of sferics, a group of radio atmospheric effects that occur as the result of lightning. Labeled whistlers, hooks, and tweaks, the rising and falling bird-like calls are the result of the electromagnetic energy created by lightning shooting up and down the planet at unfathomable speed, to be picked up by a special receiver. The unique sound pattern created by the electromagnetic field of Earth has also influenced many musicians and composers, especially Alvin Lucier, whose 1981 sound installation, Sferics, directly included these ionospheric disturbances.
Steven P. McGreevy, a member of the radio and plasma research group at the University of Iowa, has been studying and recording these natural radio patterns:
ManitobaRecorded on August 23, 1996 in Manitoba, Canada—listen for the initial static lightning burst and then a series of whistlers shooting around the planet.