Scientists glimpse embryonic galaxies

American and European astronomers have unveiled snapshots of the universe nearly 90% of the way back to the big bang.

First they obtained images, using a combination of radio, optical and x-ray telescopes, showing the formation of clusters of galaxies when the universe was 5bn years old, a little more than a third of its present age.

They then peered back further in time, to find embryonic galaxies a mere 1.5bn years after the birth of the cosmos. These baby galaxies existed inside a still-developing cluster, the most distant proto-cluster ever found, they report in Nature today.

They used the Hubble space telescope and the Chandra X-ray observatory to study the cluster which is known as RDCS1252 9-2927 and a much older proto-cluster called TNJ1338-1942. In effect, they were collecting light which had been travelling towards Earth for up to 12 billion years.

The visible modern universe seems to be composed of about 200 billion galaxies each with about 200 billion stars, grouped into distinct clusters. Since at its birth the universe must have been one dense ball of unimaginable heat, the puzzle has been when did this clustering begin?

"Until recently, people didn't think that clusters existed when the universe was only about 5 billion years old," said John Blakeslee of Johns Hopkins University in Baltimore, author of a study in the Astrophyical Journal.

George Miley of the Leiden Observatory in the Netherlands, and author of today's paper in Nature said: "Even if there were such clusters, until recently astronomers thought it was almost impossible to find clusters that existed 8 billion years ago. In fact, no one really knew when clustering began. Now we can witness it."

The visible universe is quite literally a mystery. All the stars and planets and the gas and dust in between them add up to about 4% of the whole. About 23% of the mass of the universe is undetectable and has been labelled dark matter. No one knows what it is made of.

In recent years, astronomers have become aware that the remaining 73% is even more mysterious. They propose that it made up of dark energy which pushes the galaxy clusters away from each other at an accelerating rate. The pictures published today are part of a closer look at the early history of the stars and the process which makes them cluster.

"It is a case of the rich getting richer," said Dr Blakeslee. "These clusters grew quickly because they are located in very dense regions so there is enough material to build up the member galaxies very fast."

Dr Miley said: "Massive clusters are the cities of the universe, and the radio galaxies within them are the smokestacks we can use for finding them when they are just beginning to form."

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