|Artist's concept of a black hole.|
Still more X-ray light is generated when some of the material swirling into the black hole doesn't fall in but rather is spit out at incredibly fast speeds (close to the speed of light). To understand why some material is spit out, think of the analogy of someone trying to eat too much food at once. Such a messy eater will have food fall from their mouth.
Black holes are like such messy eaters. Some material won't reach the event horizon but instead is caught up in powerful magnetic fields existing around the black hole. These "jets" not only shoot some material away. They also emit prolific amounts of energy from radio waves to visible light to X-ray light.
The jets of material shooting out from the central black hole of the Perseus cluster have blown out large holes (cavities) in the nearby gaseous medium and -- like waves propagating on a pond surface -- have set up ripples throughout the entire cluster medium. These ripples are the sound waves.