By Dr David Whitehouse BBC News Online science editor

Astronomers have discovered three of the oldest, most distant objects yet found in the Universe.

They are quasars - compact but luminous galaxies thought to be powered by supermassive black holes

Xiaohui Fan, of Arizona's Steward Observatory in Tucson, US, says they reach back to a time when the Universe was just 800 million years old.

Fan says the most distant of the three new quasars is about 13 billion light-years away and was discovered recently in the constellation Ursa Major.

Michael Strauss, of Princeton University, US, added: "These discoveries are giving us the first glimpse of the Universe when it was only 5% of its present age."

'Needle in a haystack'

When an object in space moves away from Earth, the details in its spectrum move toward longer, red wavelengths - a so-called redshift.

Astronomers believe that the most distant objects recede from Earth at the highest velocities, so the farther away an object is, the greater its redshift.

The discovery of the new quasars required a number of different telescopes with a major contribution being made by the Sloan Digital Sky Survey's 2.5-metre telescope at Apache Point Observatory in New Mexico.

Xiaohui Fan: "Like needles in a haystack"

"Finding these rare, high-redshift quasars is a needle in a haystack operation made worse by the fact that a lot of the straw looks like needles at first glance," Fan said.

"That means that there are a lot of stars which look like high-redshift quasar candidates."

Michael Strauss said: "These objects are quite faint and, although the initial spectra suggested we'd found three distant quasars, we needed observations on large telescopes to be certain of our interpretations."

Long distance

Eva Grebel, a Sloan Survey collaborator and staff astronomer at the Max-Planck Institute for Astronomy in Heidelberg, Germany, added: "Verification with larger telescopes is crucial.

"With spectra, we can distinguish distant quasar candidates powered by black holes with a billion times the Sun's mass from tiny nearby stars with only a fraction of the mass of the Sun.

"The spectra show unambiguously that the three quasars have redshifts of 6.4, 6.2 and 6.1," said Don Schneider, of Pennsylvania State University, US.

"Only one quasar had been previously known to have a redshift larger than six."

The previous record holder, with a redshift of 6.28, was discovered in 2001 by the Sloan Digital Sky Survey consortium.

Cosmologist Robert Becker, of the University of California-Davis, US, said: "The Sloan Survey has now discovered the seven most distant known quasars."

James Gunn, of Princeton University, added: "These data will be invaluable for the next major effort of the Sloan Survey quasar team, namely to characterize the evolution of quasars from their formation to the present."