How Stars Sound

The question of how stars sound arises almost immediately when we theorize about stars and space. But if it is said that there is no sound in space, how is it that scientists are gathering so much information about them and even categorizing them based on how they sound? In this mini-report we tell you.

In Space, No One Can Hear You Scream, but...

In empty space there is no air. "sound", for its part, is nothing more than a series of vibrations in the air. Therefore it could be correctly deduced that in Space we cannot hear anything. Thus, deprived of the possibility of hearing the music of the planets and stars, we would be dissatisfied spectators of an incomplete wonder. However, just because you cannot hear something in Space does not mean that the bodies and phenomena that compose it do not have the potential to produce an audible signal, even if we have to use instruments that convert light and radio waves into sound.

This procedure is the one chosen when transferring the activity of a celestial body to a type of signal that we can interpret as sound, using telescopes, radars and computers. Thanks to this translation of radio and light waves, and the interpretation that our technical and human devices make of them, we were able to form approximate sounds of, for example, how a star sounds. And based on that, deduce some data about its structure, size, gravity and state of evolution.

The previous video shows us the differences in the type of 'whistling' that each star makes (which we remember is based on the light signals they emit, subsequently converted into auditory signals). This is how we can hear the dwarf star, the sub-giant and the red giant. The categorization stems from the conceptualization and quantification of some characteristics. For example, the sound represents variations in the star's brightness; the tonal variations come from the enormous sunspots as the star rotates. The whistle is part of the granulation that exists on the star's surface, based on the rising of hot gas and the descending of cold gas, which creates cold patches that flicker. That flickering is what is detected by the Kepler space telescope and scientists can translate light into sound.

Categorizing Stars by Their Sound

The tonal variations of sunspots indicate the rotation speed of a star, and if there is not too much whistling from granulation, scientists recognize these stars as dwarf stars similar to the Sun. If there is a smaller tonal variety, we are talking about a slow-rotating star, and if at the same time there is a lot of granulation, we are facing a sub-giant star. Finally, with a smaller tonal variation and a huge amount of whistling from granulation, what we are hearing is a star with very low rotation speed and massive size, like a red giant.

The Importance of Listening to Stars

Science regularly seeks ways to make the analysis of the Universe more accessible and less laborious. This does not imply that scientists are lazy, but that there is an imperative need for speed, since our life is short and the Universe seems to be infinite (even though it is not). Faced with the idea of an intelligent extraterrestrial presence and with the hope of finding planets habitable by humans, procedures that shorten distances and times are fundamental, and in this case the categorization of stars can help us find faster some extrasolar planets in the path of these in front of their host star, their Sun.

The Impossible Possibility of Hearing a Star Up Close

Leaving aside the technique and following the theorization that encouraged us in the first place, we wonder about the real possibility of hearing a star without instruments or technical translation. The primitive answer is negative, for the reasons explained above. Now, in the case of a Supernova (a stellar explosion), the scenario could be 'dressed up' a bit so that it is possible to hear a star 'by ear', that is, without any type of technical translation.

The possibility lies in the fact that when a supernova explodes, the detonation expels a massive amount of stellar material into space, and perhaps that material could generate the medium through which sound waves could travel. The first wave would travel at more than 32,186 kilometers per second with a charge of 10^44 joules of energy, which is equivalent to 10^48 (or 10^27 in the American and French system) thermonuclear devices of 2 megatons of power detonated simultaneously, according to Charles Liu from New York University.

This is obviously impossible in a real situation, since there is no way to get close enough to a star to hear the sound it would make if it exploded, because the heat would melt us millions of kilometers before being within an audible range. But well, maybe someday we will find a way to create a material so resistant to heat and stellar explosions that it will let us hear the sound of a supernova, although that would probably be the last thing we do in our lives.