4 ms·

>This is a constant supersonic wind of ionised plasma that streams out from the Sun in all directions.... Can someone tell me what "supersonic" means in a near

• brundolf 6y ago
  [deleted]
  • noxer 6y ago
    Everything that moves, moves supersonic if the speed of sound is 0. >I assume it's being compared to the speed of sound through Earth's air. That roughly 1.2 km/h in space that is nothing. Solar wind are like a 1.6 million km/h
    • deleted 6y ago
      [deleted]
• 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 ago
      That, 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.