• Unification model: Have accretion disk around central supermassive black hole, nearby broad line region, farther out narrow line region, dusty torus, and in some cases also jets.
• Type 1: Observe from above, looking down on disk. Unabsorbed, see both broad and narrow lines. If jet is present, is reasonably bright
• Type 2: Observe from side, looking through dusty torus. Absorbed, see only narrow lines, no broad. If jet is present, it is much less bright than lobes
• Cosmic lighthouses: Can study material between us and distant quasar by looking at absorption against bright quasar spectrum
• Superluminal motion: Jet can appear to move faster than light; effect is caused by jet pointing towards us, and blobs moving at rapid (but sublight) speeds towards us

• Active galactic nucleus: Bright center of galaxy: emission fueled by accretion onto supermassive black hole
• Quasar: Traditionally used to refer to particularly luminous AGN
• Blazar: Radio-loud source viewed right down the jet. Optical spectrum is featureless (jet dominated), radio morphology is core-dominated
• Microquasar: Star plus stellar-mass black hole, with accretion disk and jets similar to quasars but on smaller scale. Useful to study because events occur more rapidly with microquasars

This famous object is a so-called planetary nebula that represents a phase of stellar evolution that the Sun should experience several billion years from now. When a star like the Sun begins to run out of fuel, it becomes what is known as a red giant. In this phase, a star sheds some of its outer layers, eventually leaving behind a hot core that collapses to form a dense white dwarf star. A fast wind emanating from the hot core rams into the ejected atmosphere, pushes it outward, and creates the graceful filamentary structures seen with optical telescopes. Chandra's X-ray data (colored in blue) of NGC 6543 shows that its central star is surrounded by a cloud of multi-million-degree gas.