"Supermassive black holes inhabit the centers of galaxies. If these black holes are actively accreting material, they too can emit powerful x-rays. One example lies at the center of Centaurus A, where an accretion disk fires a jet of particles 15,000 light-years into space. Hundreds of other x-ray sources—stellar black holes and neutron stars—also inhabit Centaurus A."
From "Super X-ray Vision," December 2002, National Geographic magazine