Explanation :
Our solar system was formed about 4.6 billion years ago. It is formed when gravity exerted low-density cloud of interstellar gas and dust. The massive cloud of gas and dust is called as Orion Nebula.
In a small area, the overdensity of clouds occurs. This caused the contraction, to begin. Due to this contraction the potential energy gets converted into kinetic energy of individual gas particles.
Hence the correct option is " materials were pulled together by the gravity". This is the one of the evidence used to indicate the beginning of the solar system.