But the reason for this is still not clear. The main goal of the project was to study the Universe when it was 7 billion years old or around half its current age. The recently completed infrared sky survey has detected over 50,000 galaxies in a patch of sky covering roughly the area of a full Moon. Although the Cambridge team has so far analysed only one fifth of the data, they have already found that there are three times as many very red galaxies as expected. One possibility is that these galaxies have more old stars in them than expected.
Old stars tend to be large and relatively cool - hence the red colour.
A second possibility is that the galaxies are very dusty. Just as dust in the atmosphere creates red sunsets, so dust clouds in galaxies scatter red light and change the light they emit. A second significant result is the discovery that these red galaxies seem to clump together much more than galaxies in the nearby Universe. One possible explanation is that these red galaxies are merging with each other to form single more massive galaxies. This merging process would explain why the astronomers are seeing more galaxies in the past than they expected.