Although most of space is essentially a vacuum providing no medium for sound waves to propagate through, a Galaxy cluster, on the other hand, has ample amounts of gas drifting between the hundreds or even thousands of galaxies within it.

虽然太空的大部分本质上是真空，没有提供介质让声波传播，但另一方面，一个星系团，拥有大量气体在其内部数百甚至数千个星系之间漂移。