Fgrav = G*(Mm)/r^2
With Fgrav being the gravitational force
G = Gravitational constant = 6.67*10^-11
M = biggest mass
m = smallest mass
r = distance between the masses
For 2 10kg bowlingballs laying 1 meter apart:
Fgrav = (6.67*10^-11)*(1*1)/(1^2) = 6.67*10^-11 Newton
As you can see, almost nothing, but still something. In space this tiny force will result in an accelaration and thus movement of the balls towards eachother.