The discovery of a rich cluster of hundreds, possibly thousands, of galaxies in deep space suggests the universe evolved into its present form far sooner than was once thought, astronomers say.
The sphere-like cluster of galaxies is the most distant massive structure yet detected in the universe, say the European Space Agency (ESA) and NASA.
The research, which will be published in the Astrophysical Journal, describes a huge cluster some nine billion light years away, in the constellation Pisces Australis (the Southern Fish).
That's about half a billion light years further than the previous record holder for a formed galaxy.
The universe is calculated to be about 13.7 billion years old, born from the Big Bang, the explosion that 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," says US astronomer Dr 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."
Dr Piero Rosati, an astronomer at the European Southern Observatory (ESO), based in Germany, agrees.
"We have underestimated how quickly the early universe matured into its present-day incarnation," he says. "The university has grown up fast."
Galactic clusters in the making
Until now, the earliest evidence for the timetable of galactic development has come from proto-clusters, galactic clusters in the making. Analysis of their light shows they are up to 10 billion years old.
But this yardstick gives no indication about 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.
These galaxies are also 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.
Information from multiple telescopes
The newly-discovered cluster has been named XMMU J2235.3-2557, after ESA's orbiting telescope, the XMM-Newton.
The 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.
The researchers 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," say the space agencies.
"Other clusters undoubtedly lie hidden in the data archive waiting to be discovered."