It’s Algore’s mothership. Please take him back.
1. It was a small black hole caused by turning on that atom-smasher :)
OR
2. It was a test of a Russian missile with some new type of antimissile countermeasure.
OR
3. It was a very powerful blue-green laser show projecting onto a fogbank or ice crystal fog. But I’ve never seen a system that could actually project an image onto a plane (which this seemed to do). It’s possible that it could be done with interference (of the optical kind).
In any case, it was pretty spectacular from the pictures and videos I’ve seen.