It's important to clarify that the concept of "sources of gravity" is a bit misleading. Gravity is not something that is "sourced" in the same way that light is emitted from a star. Instead, gravity is a fundamental force of nature that exists everywhere in the universe.

However, we can talk about the main contributors to the gravitational field in our galaxy:

1. Stars: Stars are the most visible and obvious contributors to the galaxy's gravity. They are massive objects and therefore have a strong gravitational pull. The combined gravity of all the stars in the Milky Way keeps the galaxy together and influences the motion of everything within it.

2. Dark Matter: While we cannot directly observe dark matter, its gravitational influence is undeniable. Astronomers estimate that dark matter constitutes the majority of the galaxy's mass. It is thought to be spread out throughout the galaxy, contributing significantly to its overall gravitational pull.

3. Gas and Dust: While less massive than stars or dark matter, the interstellar gas and dust that fills the Milky Way also contributes to its overall gravity. Although its individual gravitational pull is relatively weak, the sheer vastness of the interstellar medium adds up to a significant force.

Therefore, while there are not three specific "sources" of gravity, the primary contributors to the gravitational field in our galaxy are stars, dark matter, and interstellar gas and dust.