Quotes from the news wire:
This is the first time that such a large population of massive galaxies was confirmed during the first 2 billion years of the 13.7-billion-year life of the universe. These were previously invisible to us, this finding contravenes current models for that period of cosmic evolution and will help to add some details, which have been missing until now.
Previous studies have found extremely active star-forming galaxies in the early Universe, but their population is quite limited, star formation in the dark galaxies we identified is less intense, but they are 100 times more abundant than the extreme starbursts. It is important to study such a major component of the history of the Universe to comprehend galaxy formation.