A black hole with the mass 12 billion times that of our sun has been discovered and appears to have attained that size by the time the universe was less than a billion years old, going against current theories of black hole formation, astronomers say.

The black hole, 12.8 billion light years from Earth, is powering a quasar with a luminosity of 420 trillion suns, the brightest quasar in the early universe ever observed, they say.

Current theories hold that the black hole and its quasar could not have grown so large and so bright so soon following the birth of the universe in the Big Bang around 13.7 billion years ago, astronomers say.

"We don't currently have a satisfactory theory to explain it," says study lead author Xue-Bing Wu of Peking University and the Kavli Institute of Astronomy and Astrophysics.

The researchers suggest that to reach such a staggering size in just 900 million years, the black hole must have been gobbling up surrounding interstellar mass at the maximum possible rate during that entire time.

However, the radiation energy of the quasar created by the black hole, powered by gas heated to glowing as it falls into the hole, should have begun to limit that eating frenzy before such a size was reached, they say, by forcing new material out of the gravitational pull of the black hole.

"How can a quasar so luminous, and a black hole so massive, form so early in the history of the universe, at an era soon after the earliest stars and galaxies have just emerged?" says study co-author Xiaohui Fan, a University of Arizona astronomy professor. "And what is the relationship between this monster black hole and its surrounding environment, including its host galaxy?"

Astronomers are trying to come up with the solution to the puzzle of a black hole so big forming so early after the birth of the universe, which goes against the growth limits posited by current assumptions, the astronomers say.

"It either requires very special ways to grow the black hole, or requires that a huge seed black hole existed when the universe was less than 300 million years old," Wu says.

The researchers say they'll mount a campaign of follow-up observations in the months ahead, including the use of powerful instruments like the Hubble Space Telescope in an attempt to peer even further back into the universe's history to study this strange and confounding cosmic phenomenon.