Telescope catches early starlight

By Jonathan Amos
BBC News science reporter, in Birmingham

Nasa's Spitzer infrared telescope More details

Astronomers have seen the light coming from what could be some of the very first stars to shine in the Universe.

These ancient objects burst into life probably no more than 600 million years or so after the Big Bang itself.

The discovery, announced at the UK National Astronomy Meeting, suggests the evolution of galaxies got under way much earlier than previously believed.

"I hope this will scare the theorists," Dr Andrew Bunker, from the UK's Exeter University, told the BBC News website.

"It's always one of the big goals of astronomy to improve our understanding of science."

Different view

Bunker's UK-US group used images from the Hubble Space Telescope and the Keck Observatory in Hawaii to chase down and describe some of the faintest and most distant galaxies yet found.

These are targets that have redshifts of six. This is a measure of the degree to which the light from these galaxies is being "stretched" by the expansion of the Universe.

The greater the redshift, the more distant the object and the earlier it is being seen in cosmic history.

The team then went to the Spitzer space telescope which, with its remarkable infrared detectors, can pull out information that is different from that of Hubble.

"The Hubble images tell us about the new-born stars, but the new infrared images taken with the Spitzer space telescope give us extra information about the light that comes from older stars within these distant galaxies," said Laurence Eyles, who studied the Spitzer data as part of his research for a doctorate at Exeter.

And Dr Bunker added: "There are stars there that formed before the epoch we see them - and we see them about one billion years after the Big Bang. Our evidence indicates these stars formed maybe 300 million years before that."

First light

This goes into redshift 10 territory and asks new questions about the timing of key events in the early Universe.

"The real puzzle is that these galaxies seem to be already quite old when the Universe was only about 5% of its current age," commented Professor Richard Ellis, of Caltech, US.

"This means star formation must have started very early in the history of the Universe - earlier than previously believed."

It is possible the stars seen in the Spitzer data were among the very first populations that ended the so-called "Dark Ages".

The term, coined by the English Astronomer Royal, Sir Martin Rees, refers to the period in cosmic history when hydrogen and helium atoms had formed but had not yet had the opportunity to condense and ignite as stars.

Nobody is quite clear how long this phase lasted and the detailed study of the cosmic sources that brought this period to an end is now a major goal.

"We now know there was some star formation going on at redshift 10. This is the first evidence of that," said Dr Bunker.

A paper written by the UK-US team has been submitted for publication in the Monthly Notices of the Royal Astronomical Society (RAS).

The RAS National Astronomy Meeting is being held at the University of Birmingham.