Artist's concept of a black hole.

A black hole is an object whose gravitational pull is so intense that nothing, not even light, can escape it once inside a certain region called the event horizon. As gas and dust (or even entire stars) are sucked in, the material is accelerated and heated to very high temperatures. This in turn results in the emission of X-ray light. Black holes containing lots of nearby gas and dust such as this Perseus cluster galaxy produce tremendous amounts of X-ray light.

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.