Simplify the following text for a Grade 8 native English-speaking person.
Original: Such a shock wave would have also caused the nebula to rotate and gain angular momentum .
Simplified: Then , about 4.68 109 years ago , the solar nebula began to contract , rotate and gain angular momentum . This may have been triggered by a star in the region exploding as a supernova , and sending a shock wave through the solar nebula .