In theories of quantum gravity, the graviton is the hypothetical elementary particle that mediates the force of gravity. While there is no complete quantum field theory of gravitons, they play a huge role in understanding physics and gravitation.
Gravitons are massless, but they do carry energy. They can create more gravitons, and like other quantum particles, they carry a lot of energy, or momentum.
In theory, gravitons could be detected. However, in practice, they cannot. The problem is because gravitons interact extraordinarily weakly with matter, there is simply no physically realistic equipment to detect a single graviton.
In this TED talk, Claudia de Rham, an assistant professor of physics at Case Western Reserve University, talks about her research in theoretical cosmology, and exploring field theory models of gravity. Her theory is that gravitons could account for the accelerated expansions of the Universe. Listen to her talk about the nature of gravitons.