Graviton

The graviton applies a tiny force as it impacts the nuclei of atoms.
All atoms themselves have these graviton particles in orbit around them. If you gather a lot of atoms together the population of orbiting gravitons increases proportionately. As a result, a large asteroid for example will have more gravity than a small one.
Because the graviton is a particle that has force (gravity), it is classed as a gauge boson. Other gauge bosons include the photon, the gluon, and the W and Z particles.

If someone found one, it could lead to a theory which would join the four main physical forces: electromagnetism, gravity, strong force and weak force.

References

Category:String theory
Category:Relativity
Category:Subatomic particles