BlackHole

From 911Encyclopedia:

The so called "black hole" refers to a picture, which shows a hole outside the attacked North Twin Tower, where one can recognise, that the fire didn't burn anymore. This points on the fact, that there wasn't enough oxygen to increase the fire. This official photo didn't appear again in the media, but circulated heavily on the internet. (-> Twin Towers, attack) (See MeltingSteel)