N.A.S.A.'s Kepler space telescopes recording the imaging of gravitational lensing of a white dwarf star system as reported in an article at physics.org. Gravity is quite interesting for its profound effects upon all life as well as because of its macroscopic observable field. Additionally gravitons or whatever other forces makes gravity a purely attractive power have not been discovered.
If gravitons exist they are believed to be very small-even near the Planck length. They may be tinier even than quarks or photons, travel at the speed of light and possibly faster in extra dimensions because of different distance scales, and may be the result of very, very tiny bits of radiation by quarks and other elementary particles that cumulatively add on to larger particles creating in effect a positive magnetic-like effect on mass and energy. Gravity may act as a binding force upon other mass in proportion to its total local amount and fall off in power as gravity moves away from its mass emanation source. Gravitons may be less interactive than neutrinos and hence very hard to detect. The content of this paragraph is soley conjecture and not intended to be used in prep for any kind of exam.