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active galaxy

British  

noun

  1. Also called: active galactic nucleus.  a galaxy that emits usually large amounts of energy from a very compact central source, such as Seyfert galaxies, radio galaxies, and quasars

"Collins English Dictionary — Complete & Unabridged" 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
active galaxy Scientific  

  1. A galaxy emitting unusually high quantities of radiation from an active galactic nucleus at its center. Some active galaxies emit more energy in radio wavelengths than they do visible light. Seyfert galaxies are examples of active galaxies.

  2. See more at galactic nucleus

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

NGC 4945 is an active galaxy about 13 million light-years away in the southern constellation Centaurus.

From Science Daily • Jan. 12, 2024

An active galaxy has an unusually bright and variable center powered by a supermassive black hole that heats a surrounding disk of gas and dust through gravitational and frictional forces.

From Science Daily • Jan. 12, 2024

The detection of neutrinos ostensibly coming from this active galaxy is a big deal.

From Scientific American • Dec. 20, 2022

“Where exactly in the active galaxy, the neutrinos are produced will be a matter of debate,” he added in an email.

From New York Times • Jul. 12, 2018

Why could the concentration of matter at the center of an active galaxy like M87 not be made of stars?

From Textbooks • Oct. 13, 2016

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.