from The American Heritage® Dictionary of the English Language, 5th Edition.
- noun A galactic nucleus that emits more radiation than can be accounted for solely by light from the stars it contains.
from Wiktionary, Creative Commons Attribution/Share-Alike License.
- noun astronomy A compact region at the center of a
galaxythat has a much higher than normal luminosityover at least some portion, and possibly all, of the electromagnetic spectrum.
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