Researchers are going on about the interaction of photons with gravity.
Photons are considered to be massless particles and gravitational force is by the virtue of mass. So, it can be explained on the basis of the mass factor.
But, many experiments show that photons or light beams tend to bend by the influence of a strong gravitational force.
Well, that is a concept of a higher level but for now two things should be kept in mind.
1) Photons are considered to be massless.
2) Gravity acts by the virtue of mass.