There is a couple of questions that have arisen after i read about the general theory of relativity. 1. Should it be possible in principle for a photon to circle a star? 2. Do binary stars rotating around a center of mass radiate gravitation waves? 3. How are gravitational waves emitted? 4. The twin trip example of the special theory of relativity seems to contradict the general theory of relativity. According to the second stated, a clock near a massive star ticks slower than a clock on a orbiting planet. But the twin trip states that a guy in a spaceship ages more slowly when leaving earth, hence stating that the clock ticks slower than the correspondin one on earth. Isn't gravity stonger on earth?