Since the divergence is a scalar, what does the vectors in the corresponding graph means and how are the directions and magnitudes of the vectors relate to the divergence?

Divergencecan represent the rate of change per unit volume when the fluid is in motion. Simply put, the area where the fluid is concentrated in motion is the spoke, and the area where it is dispersed in motion is the divergence. A negative divergence value is an irradiation

In a vector field, the divergence represents the amount of vector field flow that originates from or converges towards a given point. While the divergence itself is a scalar quantity, it is often visualized using a vector plot where each vector represents the direction and magnitude of the flow at a specific point in the field. The direction of the vectors indicates the direction of the flow, while the length of the vectors represents the magnitude of the flow. When the vectors are close together or pointing towards a central point, it indicates a high degree of convergence or compression, resulting in a positive divergence value.