The soul orbs in Portal

Solution 1:

It seems that those orbs are indeed a bug from the game. Looking at this guide, it is explained how they are created:

I came across this glitch completely by accident. These "orbs" don't do anything to you or your game and you can walk straight through them with no effect. If you have a slow computer or one that can't handle a lot of moving entities/animations, don't spawn too many. They'll slow down your framerate quite a bit. Other than that, these things just look cool!

It's possible to see blue and orange versions of those orbs, like you can see in the guide above. Some other people have been reporting about this bug, for instance in this Reddit thread:

It's a Orange Portal bullet. This is definitly a bug. You actually shooted the Orange Portal 2 times on a material that not allow's that! So in the First stage comes the effect, and in stage 2 comes the static effect that destroys the Orange Portal and crashes the code. Then it will become static ;)