Spiral Galaxies are collections of dust, gas, and billions of stars forming a flattened disk. But, at the very heart of this galaxy lies a monster. Astronomers have discovered that every major galaxy has, at its core, a huge black hole with millions or even billions of times the mass of our Sun. In a normal, or quiescent, galaxy, this picture is fairly serene. But, not all galaxies are quiet. In some, gas and dust are actively falling onto the central black hole. This material forms a flattened disk called an accretion disk. Friction and other forces heat the disk to millions of degrees - so hot that it emits x-rays. The disk becomes incredibly bright, outshining all the rest of the galaxy. When this happens, the galaxy is said to be "active". Some active galaxies blast out beams of matter and energy emanating from near the central black hole. These jets are powered by the accretion disk - probably focused by the disk's rotation and magnetic fields. But their ultimate nature is still not well understood by scientists.