So a galaxy is a collection of stars and planets
kept together by gravity with a black hole in the
middle. Since most of a galaxy is empty space,
there is no air in the vast majority of a
However, the gravitational pull of a planet is
sometimes enough to keep gases on the surface
which we call an atmosphere. If this atmosphere
contains a gas mixture that is the same as on
Earth, we would consider that this planet has air.
It is possible that there are planets in other
galaxies that have air like ours, but at the
moment we haven’t found any for sure.