Image caption Quasar impression: The giant black hole shreds the gas and dust in the disc that surrounds it, making this material shine out across the cosmos

Astronomers have spied a monster black hole - the brightest object yet seen in the early Universe.

Detected by a UK telescope in Hawaii, the hole is seen as it was a mere 770 million years after the Big Bang.

This means its light has taken an astonishing 12.9 billion years to reach us here on Earth.

Scientists report the discovery in the journal Nature. They say it will help them understand better the conditions that existed in the early cosmos.

It should also provide new insights on how so-called super-massive black holes come into being.

As has become clear from a number of recent observations, these giants seem to have established themselves very early on in the Universe.

"Technically, this object is what we call a quasar," explained Dr Daniel Mortlock, the lead author of the Nature paper from Imperial College London.

"The super-massive black hole itself is dark but it has a disc of gas or dust around it that has got so hot that it will outshine an entire galaxy of stars."

As bright as it was in the early Universe, the object appears now to us on Earth as just a faint dot in the infrared.

It glows in this part of the electromagnetic spectrum because the brilliant ultraviolet light with which it once shone has been stretched to longer wavelengths on its passage through the expanding cosmos.

Image caption We detect ULAS J1120+0641 on Earth as a faint dot in the infrared part of the light spectrum

The UKIRT Infrared Deep Sky Survey (UKIDSS) has been trawling the sky looking for such light sources, knowing that any detection is likely to be a very distant object.

The newly identified quasar has been designated ULAS J1120+0641. It is not the most distant object seen in the Universe - that record probably goes to a gamma-ray burst (GRB), the light from an exploded star. But the quasar is hundreds of times brighter than the GRB, and certainly bright enough to allow scientists to start to probe the object and its surroundings in some detail.

Theory holds that the very young cosmos would have been filled with neutral hydrogen. Then, as the first stars burned bright, they would have "fried" this neutral gas, ripping electrons from protons to produce the diffuse intergalactic plasma we detect between nearby stars today.

The transition between these periods is dubbed the "epoch of re-ionization", and is considered to be a milestone in cosmic history and astronomers are very keen to tie down the timing of when it occurred.

The light from ULAS J1120+0641 displays the characteristic signature of neutral gas, indicating that, at 770 million years after the Big Bang, the process of re-ionization had some way to go before the process was complete.

Image caption The UK Infrared Telescope (UKIRT) is sited on a mountain top in Hawaii

Dr Mortlock told BBC News: "This is the first time we have seen a quasar that we are sure is sitting in a significantly neutral Universe - it might be 10%, it might be 50% of the hydrogen is neutral - but all the other ones we've seen, even a 100 million years later, had a fraction of the neutral gas we see in our quasar. Others we've detected had more like 1% or 0.1% of neutral hydrogen. So we see this quasar before the epoch of re-ionization has ended."

What is a puzzle is the scale of the black hole driving this quasar. It has a mass two billion times that of the Sun.

Its detection is one of a number lately that have indicated the presence many super-massive objects in the early cosmos. Scientists are struggling to explain how these objects could have evolved so big, so fast.

"It is safe to say that the existence of this quasar will be giving some theorists sleepless nights," observed Chris Willott from the Canadian Astronomy Data Centre in a News and Views article in Nature.

Jonathan.Amos-INTERNET@bbc.co.uk