First light at dawn of the universe

The blue objects in these pictures are thought to be the earliest galaxies to form in the universe, and they could overturn a long-standing theory that the cosmos is filled with "dark matter".

The research, published today in the science journal Nature by scientists from the University of Durham, shows that the first galaxies formed when the universe was about 5 billion years old, one-third of its current age. The galaxies are blue because the stars in them are very young; older stars would be redder.

But at the same time, the theory of "cold dark matter" - which suggests that interstellar space is filled with matter which cannot be observed directly because it does not give off light or heat - will come under strain from these results, according to the researchers.

Cosmology theory suggests that after the "Big Bang" 15 billion years ago, the matter in the Universe clumped together under gravity to form stars, and that these then clumped into larger groups of stars - the galaxies.

"In the standard version of `cold dark matter', the galaxies continue to form under gravity up to the present day," said Tom Shanks, who led the team at Durham's department of physics. "But these galaxies [in the picture] have formed rather early for that model."

Nigel Metcalfe, another team member, said "The dark matter theorists can squirm about, but it's a solid problem - there are too many of these young massive galaxies for the simple cold dark matter theory."

The pictures were produced using the William Herschel Telescope in the Canary Islands and the UK Infrared Telescope in Hawaii. They can see a million faint galaxies in an area of sky the size of the Moon, each one a million times too faint to be seen with the naked eye.

The galaxies' age was worked out by determining the "redshift" of their light - caused by them receding as the universe expands. The further away, and older, something is, the more its light is reddened.

Dark matter theory has developed because astronomical observations of the movements of galaxies suggest that something invisible is affecting them. Cold dark matter theory says this is caused by as-yet undetected particles, though other explanations, such as planet-sized objects which do not radiate heat, have been proposed.