**But is all matter composed of gravitationally trapped energy particles? ** No- only matter captured by black holes. However, if axions exist, they may be gravitationally trapped. But there is no way for them to be detected.

**Is any of matter composed of gravitationally trapped energy particles -- proven for sure? **
Not proven- but the result of the theory of general relativity. There is evidence that black holes exist from the motion of matter outside of the black hole- but no direct evidence of matter within the black hole. There is no theory or data suggesting that ordinary matter traps other matter gravitationally. Gravity is the weakest of the four forces by orders of magnitude.