A two-dimensional analog of four-dimensional spacetime curvature. The yellow area indicates the presence of mass. When the mass density becomes too great for a given radius, the surface will "break" and the yellow area will disappear—indicating the mass has now become a black hole.
An embedding diagram may be visualized as a stretched rubber sheet onto which a heavy mass is placed, causing the sheet to curve in the vicinity of the mass to form a depression in the sheet. This model is based on the Schwarzschild solution of the Einstein field equations of general relativity for the gravitational field of a non-rotating, spherically symmetric body.