Question

main source of helium is

Answer 1

Your answer is here -
Nebula contains the matter from the supernova explosion also, which inturn increase tge force of attraction, as the Gravitational forcw start to increade due to more particles. The temperature of center of star increases, pressure increase so much centre (Core) to start to reach million of degrees, which intiate fusion reaction. Similarly higher atomic particles produces, when the star dies, the half producd particles get through out into space. which are used by formation of another stars or get trapped in atmosphere like in earth..