Even if in the Earth we can hear many sounds and we communicate verbally, in the space it doesn’t happen the same thing. In the space sounds can’t be heard, and if they exist, they are too low so that our ears can hear it. The sounds in the space will never be possible to be heard by our ears.
To what is it due?
The sound is a pressure wave, and for this reason it needs an elastic medium in order to spread away. This medium is proportioned by the gas molecules. The space isn’t an elastic medium, and it is for this reason that it isn’t very likely that we could hear any sound in it. However, this doesn’t mean that there isn’t sounds.
When an object moves, either a guitar string or fireworks, acts onto the air molecules which are nearby to it. These molecules collide against those that are the nearest to them, which at the same time hit against the following. This movement, which is spread along the air as a wave, is the one that, when it arrives to the ears, it is interpreted as a sound.
Could sounds in the space be heard?
Even if in a small quantity, in the space there is some gas, which permit the sound waves to propagate, but the interstellar gas is a lot less dense than the Earth’s atmosphere. The air of the Earth atmosphere has approximately 30 trillions of millions of atoms per cubic centimetre. In comparison, in the space there is an average of 2 atoms per cubic centimetre.
Even if we were situated beside a gas cloud, which contain many atoms, and a sound moved closer towards us, only some atoms per second would arrive to our eardrums, thing which wouldn’t be sufficient for us to hear anything.
This phenomenon also takes place on Mars. The density of Mars’ atmosphere is only of 1% in comparison to our atmosphere. On the Earth, due to its big air density, a sound can go across a kilometre distance before to be extinguished by the air, but in Mars a sound would be inaudible after it had traversed 15 metres.
The space is never in silence, there always are different sounds, even if they are too low for us to hear them. This is the case of the black holes, which emit their one sounds. One of them, the black hole named Chandra, situated in the Perseus galaxies, at about 250 million light years from the Earth, emits a that sound detected by the X-ray observatory-satellite belonging to the NASA in 2003.
But in spite of being “seen”, this sound will never be heard. Indeed, it is 57 octaves deeper than a medium do: more than one thousand million times deeper than a human can hear. The deepest sound a human can hear has a cycle of approximately an oscillation every 1/20 seconds. In the case of the Chandra black hole, the cycle is of about one oscillation every 10 million years.