Astronomers, assisted by a gigantic "cosmic lens", have discovered a young galaxy in which hundreds of new stars were being born every year - at a time when the Universe was young.
By Dr David Whitehouse
BBC News Online science editor
"This unique look into a very distant, young galaxy gives us an unprecedented insight into the process that produced both tremendous numbers of stars and supermassive black holes in forming galaxies," says Chris Carilli, of the National Radio Astronomy Observatory (NRAO) in Socorro, New Mexico, US.
Peering into the heart of a quasar
"This work strongly supports the idea that the stars and the black holes formed simultaneously," he adds.
The researchers studied the active galaxy, or quasar, PSS J2322+1944, about 12 billion light-years from Earth. At the distance of this quasar, the scientists see the object as it was when the Universe was less than two billion years old, about 15% of its current age.
To detect the star-forming disc buried deep inside the quasar, the astronomers needed to observe radio emission from the carbon monoxide (CO) molecule, an important component of the gas that forms stars.
They used the multiple telescopes of the Very Large Array (VLA) in New Mexico.
Unfortunately, this molecule emits radio waves at frequencies much higher than the VLA is capable of receiving.
However, the expansion of the Universe helped. At PSS J2322+1944's distance, the Doppler effect caused by the expansion of the cosmos reduced the frequency of the radio waves to a value that is within the VLA's range.
But even that was not enough. The object was too far away for the VLA to see the detail required to show the stellar disc.
Two of the VLA's many dishes
Once again, nature stepped in to help, providing another galaxy directly between the quasar and Earth to form a gravitational lens that amplified the light from the distant quasar.
"What we needed wasn't just any old gravitational lens, but a nearly perfect alignment of the distant quasar, mid-distance galaxy, and Earth - and that's what we got," says Geraint Lewis of the University of Sydney, Australia.
"We never would have seen the disc of CO gas near the centre of this galaxy without the gravitational lens," says Carilli.
"The lens boosted the signal and magnified the image to reveal the disc's structure in unprecedented detail."
The importance of the observation is that, for several years, astronomers have noted that the masses of black holes are linked in some way to the sizes of central bulges of stars in galaxies, leading to speculation that formation of the black holes and of the stars are somehow related to each other.
The idea was that the gas was being drawn towards a galaxy's central black hole is the same gas from which large numbers of stars are formed.
"This new observation gives strong support to the idea that large numbers of stars were forming in young galaxies at the same time that their central black holes were pulling in additional mass," says Pierre Cox of the University of Paris, France.
The astronomers believe that galaxies in the early Universe were frequently disrupted by nearby encounters with other galaxies, "feeding" the central black hole with gas.
The gas formed an extensive, spinning disc around the galaxy's centre, some of it eventually falling into the black hole and some of it forming new stars.
In PSS J2322+1944, the astronomers believe that new stars with a total mass equal to about 900 times that of our Sun were forming in the 13,000-light-year-diameter disc every year.