Faster than 'c' measurements that do not violate relativity theory

[FinestHour86]

Homework Statement

Some collections of stars called galaxies release jets of gas. Some of these jets have been measured to travel faster than the speed of light in a vacuum. Explain why relativity theory is not violated.

Homework Equations

This problem requires a qualitative response and no equations are required to answer it.

The Attempt at a Solution

Since according to relativity theory 'c' is a constant, I do not see how it is possible to answer this question. Seemingly this phenomenon does violate relativity theory.

 

[Mindscrape]

Though I know almost nothing about astro, I'll bet the answer has to do with the jets not actually traveling in a vacuum, and with an index of refraction that changes the speed of light in the index to be faster than the speed of light in a vacuum. That should get you started until an astro person comes along.

v=c/n

so you need n<1