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12 Cards in this Set

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  • Back
active galactic nuclei (AGN)
The centers of active galaxies that are emitting large amounts of excess energy. See also active galaxy. (p. 306)
active galaxy
A galaxy whose center emits large amounts of excess energy, often in the form of radio emission. Active galaxies are suspected of having massive black holes in their centers into which matter is flowing. (p. 306)
BL Lac objects
Objects that resemble quasars. Thought to be highly luminous cores of distant active galaxies. (p. 313)
See BL Lac objects.
cold dark matter
Mass in the universe, as yet undetected except for its gravitational influence, which is made up of slow-moving particles. (p. 311)
double-exhaust model
The theory that double radio lobes are produced by pairs of jets emitted in opposite directions from the centers of active galaxies. (p. 308)
double-lobed radio source
A galaxy that emits radio energy from two regions (lobes) located on opposite sides of the galaxy. (p. 308)
hot spot
In geology, a place on Earth's crust where volcanism is caused by a rising convection cell in the mantle below. In radio astronomy, a bright spot in a radio lobe. (p. 310)
quasar (quasi-stellar object, or QSO)
Small, powerful sources of energy believed to be the active cores of very distant galaxies. (p. 315)
radio galaxy
A galaxy that is a strong source of radio signals. (p. 304)
Seyfert galaxy
An otherwise normal spiral galaxy with an unusually bright, small core that fluctuates in brightness. Believed to indicate the core is erupting. (p. 306)
unified model
An attempt to explain the different types of active galactic nuclei using a single model viewed from different directions. (p. 313)