The graviton is a theoretical particle that scientists believe carries the gravitational force. Just like photons carry electromagnetic force, gravitons would carry gravity between masses. Though never directly observed, this particle is central to our understanding of quantum gravity.
The graviton has several key theoretical properties. It is predicted to be massless, allowing it to travel at the speed of light. Unlike photons which have spin-1, gravitons have spin-2, making them unique among force carriers. This spin-2 nature is what gives gravity its attractive character and distinguishes it from other fundamental forces.
In the Standard Model of particle physics, each fundamental force has its own force carrier particle. The electromagnetic force is carried by photons, the strong nuclear force by gluons, and the weak nuclear force by W and Z bosons. All of these have been experimentally detected. The graviton would be the force carrier for gravity, but unlike the others, it remains hypothetical and undetected.