My friend believe that light is a type of matter. He thinks that light is a matter because it can be sucked into the black hole. So, I've wondered this. Is light a type of matter, or is it just a wave. If it is a wave, how can it be sucked into the black hole. Is light effected by the gravity? How can light travels through vacuum. What is the differences between the sound wave and the light wave, apart from sound wave need medium to travel.