Science: A warm glow from the universe's distant past

The entire night sky is actually awash in infrared light, some of which was emitted when the universe was just one billion years old - a time when the first stars and galaxies began to light up an otherwise dark cosmos.

The latest finding, from the Cosmic Background Explorer (COBE) satellite, "represents a really exciting era in the history of the universe," said Eli Dwek of Nasa. The results were presented yesterday to the American Astronomical Society in Washington.

The picture on the left, above, shows the total intensity of infrared light in every direction in the sky - a total of some two billion individual measurements. The middle picture shows it after subtracting the "local" effects of light scattered from debris in the Solar System. The right picture shows what's left after subtracting the glow of the Milky Way galaxy.

What is left appears as a nearly uniform background "glow" of infrared radiation. The researchers compared the task to listening for a quiet background hum in a noisy shopping mall.

Astronomers say the findings will help explain how the first stars and galaxies formed after the Big Bang, the colossal explosion which marked the beginning of the universe some 15 billion years ago. Though the initial Big Bang fireball was unimaginably bright, it eventually faded to black as the visible light gave way to invisible infrared rays.

The COBE result "is telling us about the first activity that occurred [in the early universe] - what I would call the end of the dark age," said Sir Martin Rees, a Cambridge astrophysicist and the current Astronomer Royal. "This is an important clue to when the first stars formed, and how many stars formed before the galaxies we observe were actually assembled.

Eli Dwek added: "For the first time, we've detected a significant fraction of all the light that was emitted by all the stars over the entire history of the universe."