A very simple scene...........C&C welcome.
I think because where ever that gate leads to is only black in the background, I wouldn't recognize it as a gate. It also has no depth.
Some form of wormholey thing would bring it over more. Some lines giving some speed indication (even if that's physically incorrect) would give some hint that the triangle came from the object.
If you would not have written gate I would have assumed that is a galaxy or something.
I have to agree that it needs depth or possibly a view to what is on the other side.