Light has mass-energy, and mass-energy both affects and is affected by the gravitational field. Indeed it is theoretically possible to make a black hole out of

Light has mass-energy, and mass-energy both affects and is affected by the gravitational field. Indeed it is theoretically possible to make a black hole out of nothing but photons [1]. [1] https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics) https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics)