Show from the effective potential corresponding to the Schwarzschild metric that if \(U_{\text {eff }}\) can be used for arbitrarily small radii, there are actually two radii at which a particle can be in a circular orbit. The outer radius corresponds to the usual stable, circular orbit such as a planet would have around the Sun. Find the radius of the inner circular orbit, and show that it is unstable, so that if the orbiting particle deviates slightly outward from this radius it will keep moving outward, and if it deviates slightly inward it will keep moving inward.