NASA, on 16th December, in a news release, said that the Voyager 1 spacecraft, at the edge of the solar system, had experienced three shock waves. The third of these began as along ago as February 2014 and is still in progress as we approach 2015.
A similar kind of shock wave is produced by the Sun when it emits a coronal mass ejection, throwing out a cloud of plasma, generating a wave of energy. A video clip can be seen at www.jpl.nasa.gov/news/news.php?feature=4411. See also www.jpl.nasa.gov/video/details.php for a full list of videos on a variety of space subject.
It is thought Voyager 1 has passed into interstellar space and if so, the density of the plasma is high.