SAN DIEGO -- Astronomers have found what may be the largest structure in the observable universe -- an immense concentration of quasars and galaxies clustered across more than 600 million light-years.
The structure, which would include billions upon billions of stars like the sun, is 6.5 billion light-years away, which means the cluster existed when the universe was just a third of its present age of about 10 billion years. The light that revealed the cluster actually started its long journey before formation of the solar system, which includes the Earth.
"We have found nothing bigger in the [astronomy] literature and nobody has brought to our attention anything bigger," said Gerard Williger, a National Optical Astronomy Observatories researcher now working at NASA's Goddard Space Flight Center in Greenbelt, Md. He presented his study yesterday at the national meeting of the American Astronomical Society.
When viewed from Earth, the structure is just below the center of the constellation Leo the Lion. It spans an area of the sky of two degrees by five degrees, an area about 40 times that of the full moon as seen from Earth.
Williger said it is not known if the gathering of quasars and galaxies is bound together gravitationally or if it is a chance cluster formed by a ripple in the smooth expansion of the universe that followed the Big Bang, which is thought to have set off the formation of the universe.
"This may be an artifact of the Big Bang," he said. Conditions at that point in space, he said, may have been uniquely ripe for the quick formation of stars, galaxies and quasars.
That such a large structure could form so quickly after the Big Bang calls into question some of the traditional theories of how the universe evolved, Williger said, since it is difficult to explain how gravity could pull together such an immense cluster in a relatively short time. …