The sphere-like cluster of galaxies is "the most distant massive structure yet detected in the Universe," the European Space Agency (ESA) and NASA declared.

The huge cluster is located some nine billion light years away, in the constellation Pisces Australis (the Southern Fish) -- about half a billion light years farther out than the previous record holder for a formed galaxy, they said in separate press releases.

The Universe is calculated to be about 13.7 billion years old, born from a "Big Bang," the explosion which spewed out the hot matter that later formed the galaxies and everything in them.

As the light from the newly-discovered cluster has taken nine billion years to reach us, its galaxies were already formed when the Universe was a mere youth of five billion years old.

"We are quite surprised to see that exquisite structures like this could exist at such early epochs," said US astronomer Christopher Mullis of the University of Michigan.

"We see an entire network of stars and galaxies in place at just a few billion years after the Big Bang, like a kingdom popping up fast."

"We have underestimated how quickly the early Universe matured into its present-day incarnation," said Piero Rosati, an astronomer at the European Southern Observatory (ESO), headquartered in Garching, Germany. "The University has grown up fast."

Until now, the earliest evidence for the timetable of galactic development has come from "proto-clusters" -- galactic clusters in the making -- that have been dated by analysis of their light to be up to 10 billion years old.

However, this yardstick gives no indication as to how long it takes for these wild, chaotic adolescents to mature into galaxies as we know them today.

In the cluster observed by Mullis' team, the galaxies are smoothly elliptical -- a sign that gravitational force and the outward expulsion of the Big Bang gently sculpted them over what could be several billion years.

In addition, these galaxies are filled with stars emitting light in the red part of the spectrum, an unmistakeable sign of stellar old age.

Galaxy clusters contain hundreds to thousands of galaxies that are bound to each through the invisible tendrils of gravitational force. Our own galaxy, the Milky Way, is a relatively "low-density" region of the Universe.

The newly-discovered cluster has been named XMMU J2235.3-2557, after ESA's orbiting telescope, the XMM-Newton.

The hi-tech observatory, launched in December 1999, detects radiation in the X-ray part of the energy spectrum that is invisible to optical telescopes.

It was by trawling through archived material of XMM-Newton observations, made over the past four years, that the team spotted tantalising evidence of a very distant galactic cluster.

They then turned the eyes of ESO's Very Large Telescope in Chile's Atacama Desert onto the discovery, finding optical evidence to back the X-ray emissions.

"This discovery might be just the tip of the iceberg," ESA and NASA said. "Other clusters undoubtedly lie hidden in the data archive waiting to be discovered."

The research will be published in a fortchoming issue of a US publication, the Astrophysical Journal, the ESA press release said.

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