Why is there no sound in space?

Sound is a mechanical wave: it travels when molecules bump into each other, transferring energy from one to the next. In Earth’s atmosphere, about 25 quintillion molecules per cubic centimetre carry sound at roughly 343 metres per second. In deep space there may be only a few atoms per cubic centimetre, far too few to sustain a pressure wave. An explosion in space would produce no bang for a nearby astronaut. However, in dense nebulae or galaxy clusters, extremely low-frequency pressure waves can propagate through the hot gas. NASA “sonified” these vibrations in 2022, converting them into audible sound.