The presumed cluster of galaxies is more than 6.5 billion light-years away. Calculating the time it took the light to get here, researchers say it is seen as the universe was about one-third of its present age.

The galaxy cluster is in the largest known group of quasars, remote but intense sources of radio emissions. Quasars are galaxies with bright cores, probably powered by giant black holes. This group of quasars is known to be about 600 million light-years across. A light year is the distance traveled by light in a year -- about 6 trillion miles or 9.7 trillion kilometers.

The galaxies were revealed by light they absorbed from the spectra of even more distant quasars that are located behind the large quasar group.

If the concentration of galaxies and quasars is caused by a larger-than-usual amount of matter in the area, then traditional theories of the evolution of the universe have difficulty explaining how gravity could pull extremely massive structures together over such a large distance in such a relatively short time (keeping in mind that this structure was assembled fairly soon after the Big Bang.)

"The amount of matter connected with quasars and galaxies at such distances and distant times in the past is probably not the same as we would measure in the local universe today, so it's very important to find out how much mass we are actually looking at in the supercluster," said NASA's Gerard Williger, also of the National Optical Astronomy Observatories. "The first step is to look for signs of extra galaxies in the area, and now we have evidence for a surplus of galaxies."

The research was presented January 8 at a meeting of the American Astronomical Society in San Diego.

The massive galaxy concentration is located just south of the heart of the constellation Leo the Lion, in a region spanning some 40 times the area of the full Moon, as seen in the sky from Earth.

Williger and colleagues used the 4-meter (159-inch) telescope at the National Science Foundation's Cerro Tololo Inter-American Observatory in Chile to also find a large number of clouds of gas in the same area, which are thought to originate in the haloes surrounding galaxies.

The galaxies themselves are faint and have not yet been directly seen. However, magnesium atoms in the halo gas of the galaxies absorb light coming from quasars behind the cluster. This produces "shadows" in front of the quasars, thus revealing the existence of the galaxies. So far, 11 such faint absorber galaxies have also been found in the same space as the large group of quasars, which is nearly three times more than expected.

The group cautioned that the results need to pass the test of peer review and that more data needs to be gathered.