Explanation:
The electro magnetic force is given by
F =
where and
are charged particles
k =Coulombs constant
r = distance between two charges
And gravitational force is given by
F =
where and
are masses
G =Garvitation constant
r = distance between two masses
Now since the planets, stars and galaxies are electrically neutral, therefore they have zero electrical charge and so electro magnetic forces have no affect on these planets, stars and heavenly bodies.
Whereas the masses of the heavenly bodies are very large, so they are largely affected by the gravitational force since Gravitational force is directly proportional to the product of the masses of a body.
Therefore, though the electromagnetic force is stronger than the gravitational force, the electromagnetic force does not dominate the forces in the heavenly bodies as they as not electrically charged.