What it is: The study of objects outside our galaxy. like other galaxies, super novae, pulsars, extra galactic black holes, and other stellar objects, and some even do the possibility of life in other galaxies.

What it does: branch of astronomy concerned with the formation and evolution of Galaxies; their morphology and classification; and the examination of active galaxies, and the groups and clusters of galaxies.

There are galaxies that have other things as well not just stars, they may have life giving worlds, they may have exotic looking nebulae, and the famous Black hole.

Galaxies are extremely beautiful objects but like all things they are fairly unknown and in reality very dangerous.