Is NASA telling us something here between the lines? From the article I linked:

"The emissions are paired, going in opposite directions, creating a structure something like giant megaphones set back-to-back."

For the first time, scientists have experimentally demonstrated that sound pulses can travel at velocities faster than the speed of light, c. William Robertson’s team from Middle Tennessee State University also showed that the group velocity of sound waves can become infinite, and even negative.