This is something I just made as a little challenge, one of my teachers showed me a similar concept in unreal so I decided to try it in unity.
The way this material works is by projecting a cube map that is captured(possibly real-time) by a camera that is located elsewhere. The sphere surface is manipulated in the shader as well to make it look more interesting.
There is also a script attached to the sphere to make it pull in players that get to close and teleport them once they are fully sucked in.