Final answer:
In the interstellar space of the Milky Way Galaxy, there is on average about one atom per cubic centimeter. The air on Earth is vastly more dense, with about 1019 atoms per cubic centimeter. Although sparse, the significant volume of interstellar space results in a considerable total mass of gas and dust.
Step-by-step explanation:
The Galaxy, which we refer to as the Milky Way, is composed primarily of empty space, with incredibly low densities of matter.
In the interstellar space of our Galaxy, the average is approximately one atom per cubic centimeter.
By contrast, the air we breathe on Earth has about 1019 atoms in each cubic centimeter, which signifies a drastically higher density than what you find in outer space.
The material between stars, which includes gas and dust, is distributed in a patchy, irregular manner, with interstellar matter and dust being especially sparse.
Despite the low density, the vast volume of space in the Galaxy means the total mass of interstellar gas and dust is substantial.
Astronomers estimate this mass represents about 15% of the mass contained in stars within the Milky Way.
This suggests that there is an abundance of material available in the Galaxy to form new stars, planets, and potentially even future astronomers.