Final answer:
Dark matter constitutes the majority of the mass in the Milky Way Galaxy, significantly outweighing the mass of visible matter such as stars, gas, and dust.
Step-by-step explanation:
The majority of the mass in the Milky Way Galaxy is made up of dark matter. While the visible matter, which includes stars, gas, and dust, emits electromagnetic energy, they do not contribute as much to the galaxy's total mass.
Astronomers have gathered evidence, such as the rapid revolution of stars in the outer regions of the Milky Way and the gravitational effects on them, as well as gravitational lensing effects, to support the presence of a significant amount of dark matter.
This invisible component proves to be dominant over normal luminous matter, and our Galaxy is thought to contain about ten times more dark matter than the luminous matter. Gas and dust, although important for the formation of new stars and planets, make up only about 15% of the mass of the stars, amounting to about 10 billion times the mass of the Sun. Therefore, dark matter is crucial for maintaining the structure and evolution of galaxies and ultimately the universe.