Astronomers see galaxy ancestors shine

An international team of astronomers that includes Dr Andy Bunker of the Anglo-Australian Observatory has for the first time detected faint light from the "building blocks" of galaxies in the early Universe.

The "building blocks" are clouds of hydrogen gas that existed when the Universe was about 2.7 billion years old—a fifth of its present age.

Until now, such clouds had been known only by the "shadows" they cast as they absorbed light from even more distant quasars.

"For the first time we can tell that there were stars in at least some of these gas clouds," said Dr Bunker, Head of Astronomy at the Anglo-Australian Observatory.

"And for the first time we can estimate the sizes of the clouds."

The astronomers describe their work as the most sensitive observations ever made of the Universe.

Using the 8-m VLT telescopes of the European Southern Observatory in Chile, they repeatedly observed the same small patch of sky for a total of 92 hours.

They found 27 gas clouds, at a distance of 11 billion light years. Because light takes time to travel through the Universe, looking far out into space is equivalent to looking back in time, and so the clouds existed about 11 billion years ago, or about 2.7 billion years after the Universe formed.

"The number of clouds we’ve found is in line with our theory of how galaxies form—small proto-galaxies merging over time to build up big ones," Dr Bunker said.

"This discovery opens the door to finding large numbers of these building blocks and so being able to study in detail how galaxies like our own have come together," he said.

 More information

Dr Andy Bunker
Anglo-Australian Observatory, Sydney, Australia
+61 2 9372 4851


M. Rauch et al. "A population of faint extended line emitters and the host galaxies of optically thick QSO absorption systems." Astrophysical Journal, 1 March 2008. Online at

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