galactic nucleus

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The center of a galaxy, usually small, very bright, and containing a high density of stars and other objects.♦ An active galactic nucleus is a nucleus that emits more radiation than can be explained in terms of stars alone. Blazars and quasars are thought to be active galactic nuclei; the nuclei of Seyfert galaxies are also active, and are thought to contain an extremely massive black hole.
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“Was” is used for the indicative past tense of “to be,” and “were” is only used for the subjunctive past tense.
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