What force to scientist think was responsible for clumping matter together to form the first stars after the Big Bang?

Answer : Gravity
Explanation : Matter comes together to form stars under the force of gravity. Gravity is a force that causes all object to attract each other . This force dependent on their masses and their distance.
So, we can say that scientist know the force of gravity is responsible for clumping matter together to form the first stars after the big bang.