The unusual whistles and crackles caused by some of the meteors appearing in the sky may finally have a definitive explanation.
These quiet sounds are likely formed when bright pulses of light from the direction of a meteor heat up objects on the ground below it, according to a new study. These objects - such as leaves or hair - radiate heat energy into the air around them, resulting in pressure waves - which is essentially sound.
“We think our version is pretty compelling,” said co-author of the new study, William Sweatt, of Sandia National Laboratories, USA.
People hear these mysterious sounds when very bright meteors appear in the sky, the apparent size of which is comparable to the size of the full moon. As a rule, the mass of an object must be at least 0.5 kilograms in order for its appearance in the sky to be accompanied by such a sound. Since the meteor that flashed in the sky is very far from us, the sound coming from it would take quite a long time to reach the observer's ear, while in fact, the observers of large meteors hear the quiet crackling and whistling almost immediately when the appearance of flashes of fire in the sky.
The explanation offered by the research team, which includes Swatt, is based on the phenomenon of the so-called "photoacoustic coupling". The essence of the phenomenon is that the light emitted by a distant object heats a distant object, which, as a result of heating, itself becomes a source of radiation in the infrared range, as a result of which the surrounding air heats up and density waves are formed in it. The authors of the work conducted an experiment confirming the presence of the acoustic pairing effect: they recorded a musical composition and turned it into a sequence of light pulses, which irradiated a distant object, including a tree, leaves, and even a wig that imitates human hair. In all cases, the researchers recorded, using a microphone for this purpose, the "playback" of the transmitted audio recording (however,with very serious distortions) using an object irradiated with these light pulses.
The research is published in Scientific Reports.
