Two stars interact with each other. Star 1 has a mass $2 \times 10^{30}$ kg, and Star 2 has a mass $1 \times 10^{30}$ kg. At a certain instant ($t = 0$), Star 1 is at the origin with zero velocity, and Star 2 is at ($-1.50 \times 10^{11}$, 0, 0) m with a velocity (0, $-3.50 \times 10^4$, 0) m/s. Later, at $t = 7.5 \times 10^6$ s, Star 1 has a velocity ($-1.20 \times 10^4$, $-1.69 \times 10^4$, 0) m/s. Define the system as Star 1 and Star 2. It is an isolated system, far from other stars.