What does "active galaxy" mean?

A galaxy where a significant fraction of the energy output is not emitted by the normal components of a galaxy.

What is a synonym for "active galaxy"?

Common synonyms include: seyfert.

noun

noun ·Rare ·Advanced level

Noun

1
A galaxy where a significant fraction of the energy output is not emitted by the normal components of a galaxy.
2
A galaxy with an active nucleus (AGN, active galactic nucleus)