Gravity couples with anything that carries energy (in more precise terms with the energy-momentum tensor). Photons carry energy. Therefore there is interaction

Gravity couples with anything that carries energy (in more precise terms with the energy-momentum tensor). Photons carry energy. Therefore there is interaction between photons and gravity. In particular, you can write Feynman diagrams for the interaction between a quanta of gravity (a graviton) and a photon. Some of the simplest ones look like this: https://www.researchgate.net/figure/Tree-level-Feynman-diagrams-of-graviton-photon-transitions-3-Wavy-lines-represent_fig3_328933275 https://www.researchgate.net/figure/Tree-level-Feynman-diagr... There you can see different ways in which a pair of gravitons can interact leading to a pair of photons. If you want to dig deeper in the math behind it: https://physics.stackexchange.com/questions/335917/how-do-i-derive-the-feynman-rules-for-graviton-photon-coupling https://physics.stackexchange.com/questions/335917/how-do-i-... Regarding Hawking radiation, it's not gravity itself that causes it. It's a consequence of the existence of an event horizon. In fact, you can have a similar effect in flat spacetime (i.e. no gravity), an accelerating observer will see an event horizon and it will feel itself immersed in a thermal bath of particles at certain temperature that has to do with its acceleration. This is called the Unruh effect. Further reading: https://en.wikipedia.org/wiki/Unruh_effect https://en.wikipedia.org/wiki/Unruh_effect