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active galactic nuclei (AGN)

The innermost regions of young galaxies can be very active and radiate considerable amounts of energy. Examples for such active galactic nuclei are radio galaxies and quasars.

In current models, the energy source powering activities of such nuclei, is a supermassive black hole in the galactic centre.

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nuclei (nucleus)

Extremely dense central region of an atom, consisting of protons and neutrons held together by nuclear forces. The number of protons determines what chemical element a nucleus represents. Typical diameter for atomic nuclei are in the region of a quadrillionth of a metre= 10^-15 metres. This makes nuclei about a hundredth of a thousandth as large as atoms.

energy

Physical quantity with the special property that, in physical processes, energy is neither destroyed nor created, simply transformed from one form of energy to another. Some of the different forms of energy that are defined separately are kinetic energy, thermal energy and the energy carried by electromagnetic radiation. Processes that transform one form of energy into another take place in all machines we use in everyday life, from the engine of a subway train (electrical energy into kinetic energy of the train) to an electric blanket (electrical energy into thermal energy). One important consequence of special relativity is that energy and mass are completely equivalent - two different ways to define what is, on closer inspection, one and the same physical quantity. See the keyword equivalence between mass and energy.

current

Matter in coordinated, flowing motion - think of water flowing in a pipe. An important example is the electric current associated with moving electric charges. Electric currents are the sources of magnetic fields.

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active galactic nuclei (AGN)

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