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Part of Hall of the Universe.
An active galaxy emits up to thousands of times more energy than a normal galaxy. Most of this energy is released not in visible light but in other wavelengths, from radio waves to gamma rays. In addition, long jets of gas can spew forth from the galaxy at nearly the speed of light. This activity is driven by a supermassive black hole in the galaxy’s nucleus.
Supermassive black holes power active galaxies. No other known object could provide so much energy from so small a region. Ordinary black holes, which arise from the death of a single star, contain about ten times the Sun's mass. But supermassive black holes range from millions to billions of times the mass of the Sun. They are found at the centers of galaxies, and consume stars and gas clouds that wander too close.
When stars and gas clouds spiral into a supermassive black hole, they typically form a rapidly rotating disk, jets develop when some of the material is flung off along magnetic fields that are perpendicular to the disk.
These active galaxies send forth jets of high-energy particles that plow into the surrounding material at nearly the speed of light. When the particles slow down, their energy of motion is converted to radio waves.