Located or originating beyond the Milky Way.(adjective)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "extragalactic" in a sentence
"I thought that the article implied that the 'extragalactic' GCs joined our galaxy through the Milky Way cannibalising other, smaller dwarf galaxies."
"Some people reach for the stars, but my reach is extragalactic."
"Or not; the general topic is a hot one in extragalactic astronomy, so there's a lot of research being done."