Extragalactic astronomy is the branch of astronomy concerned with objects outside the Milky Way galaxy. In other words, it is the study of all astronomical objects which are not covered by galactic astronomy.

What is the meaning of the phrase extragalactic material?

Situated, occurring, or originating outside the Milky Way galaxy.

What do extragalactic astronomers do?

Center for Astrophysics | Harvard & Smithsonian extragalactic astronomers study galaxies in a wide variety of ways: ... Mapping stars, gas, and dust within galactic disks to understand how galaxies grow and make new stars.