3 ms·
It means that the plasma itself is traveling faster than sound waves would in that plasma. That it is not very dense doesn't change much here.
by fhars 6y ago
It means that the plasma itself is traveling faster than sound waves would in that plasma. That it is not very dense doesn't change much here.
- vl 6y ago> That it is not very dense doesn't change much here. It does matter, because at some density there are no sound waves anymore. You can’t have sound waves if particles do not collide with each other. And also speed of sound goes down as density goes down. So for this extremely non-dense plasma it’s unclear how “sound wave” is defined.
- fhars 6y agoThat, again, doesn't change the speed of sound, only the maximal frequency / minimal wavelength of sound waves in the medium. In the intergalactic medium, only wave lengths longer than several light seconds are possible, but there is enough space for them to propagate.