It also doubles
The gravitational force between two masses is expressed as:
F = G*m1*m2/r^2
where
F = Force between the two masses
m1 = Mass of object 1
m2 = Mass of object 2
r = distance between centers of object 1 and object 2
G = Gravitational constant
The exact values of G, m1, m2, and r don't matter since all except for m1 is held constant. And when m1 suddenly doubles, the force attracting the two object to each other also doubles.
