8. Let $F_{1}, F_{2}$ be the two foci of the ellipse $\frac{x^{2}}{9}+\frac{y^{2}}{4}=1$, and $P$ be a point on the ellipse such that $\left|P F_{1}\right|:\left|P F_{2}\right|=2: 1$. Then the area of $\triangle P F_{1} F_{2}$ is $\qquad$