 Gravitational field null between two point masses

Two positive point masses $M_1,M_2$ separated by $D$ have a unique intervening gravitational field zero. At distance $x$ from $M_1$, Newton's law of universal gravitation gives $M_1/x^2=M_2/(D-x{)}^2$, hence the displayed value. The signed offset towards $M_2$ from their centre of mass is $x-D{M}_2/(M_1+M_2)$. This instantaneous cancellation is distinct from a Lagrange point, which includes the centrifugal force of a co-rotating description. Along the joining line the zero is unstable: the derivative of the signed acceleration is $2G{M}_1/x^3+2G{M}_2/(D-x{)}^3>0$.