Hello again Hazoc,
Sorry for the delay, hard week for me : here is a first scene, pretty raw, where I have a sphere (symbolizing the black hole, will be black), a null and a plane parented to the camera: this plane is receiving the blackhole shader.
you will find in the material tab a material_builder with a simple snippet: the script is in it, but I don't know in Houdini what to link to what.
Hope you'll find out
thank you in advance
snippet_blackhole_shader.hip