Dictionary of Space Concepts

Short definition: An active galactic nucleus, or an AGN, is an extremely bright compact region in the center of a galaxy. The brightest, most powerful AGNs are classified as quasars. The galaxy hosting an AGN is called an active galaxy.

Detailed definition: Active galactic nuclei have a much higher luminosity than any star could produce. They emit radiation across the whole electromagnetic spectrum, from gamma rays to radio waves. Due to their extreme luminosity they can be used as a means of detecting distant objects in space.
This extreme, non stellar radiation is thought to result from the accretion of matter by a Supermassive Black Hole at the center of an active galaxy. Accretion is the process of accumulating particles into a massive object by gravitationally attracting more and more matter.

Etymology: AGN is the commonly used acronym for Active Galactic Nucleus.

Sample sentence(s): Using active galactic nuclei to measure cosmic distances could lead to a breakthrough in cosmology.

Translations:

French: Galaxie active

German: Aktiver Galaxienkern

Italian: Galassia attiva

Polish: aktywne jądro galaktyczne

Swedish: Aktiv galaxkärna

Links to Videos/Articles:

Active Galactic Nucleus. ESA/Hubble | ESA/Hubble. https://esahubble.org/wordbank/active-galactic-nucleus/

What Are Active Galactic Nuclei? (n.d.). WebbTelescope.org. https://webbtelescope.org/contents/articles/what-are-active-galactic-nuclei