This artist's impression shows the thick dust torus that astronomers believe surrounds many supermassive black holes and their accretion discs. When the torus is seen edge-on as in this case, much of the light and radiation emitted by the accretion disc is blocked, creating a "hidden" black hole.

Credit: ESA

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PARIS: A haul of hundreds of expanding supermassive black holes have been found buried deep inside numerous galaxies on the edges of the universe.

The astounding discovery is the first direct evidence that most huge galaxies in the far reaches of the universe generated cavernous black holes during their youth, around 10.5 billion years ago.

Scientists generally agree that the universe as we perceive it came into being about 14 billion years ago.

"Tip of the iceberg"

The findings – reported in the November edition of the Astrophysical Journal – more than double the total number of black holes known to exist at that distance, and suggests that there were hundreds of millions more growing in the early universe.

"We had seen the tip of the iceberg before in our search for these objects. Now, we can see the iceberg itself," said Mark Dickinson of the U.S. National Optical Astronomy Observatory in Tucson, Arizona.

Black holes are among the most powerful forces in the Universe. They are believed to be concentrated fields of gravity that are so powerful that nothing, not even light, can escape them.

Astronomers have long assumed that there were far more so-called 'active' black holes than had been observed, but were unable to find any trace of them.

These supermassive entities are known as high-energy quasars. These are a type of black hole, found in young galaxies, that are surrounded by a thick halo of gas and dust, which produces X-rays as it is sucked into the void.

The presence of X-rays, even when the quasars themselves cannot be seen, is what tipped off the scientists to the fact they had stumbled across something extraordinary.

"We knew from other studies from about 30 years ago that there must be more quasars in the universe, but we didn't know where to find them until now," said astrophysicist Emanuele Daddi, of the Atomic Energy Commission in France, who led the research.

Galactic evolution

Daddi and his team set out to study some 1,000 galaxies – about the same mass as the Milky Way – which are in the process of making stars, but were thought to lack quasars.

At nine to 10 billion light years distant, what we see today actually occurred 10 billion years ago, when the universe was still a fledgling between 2.5 to 4.5 billion years old.

The newfound quasars will help answer fundamental questions about how massive galaxies evolve. Astronomers now know, for example, that most of these galaxies steadily generate stars and black holes simultaneously until the latter become too big and impede star formation.

The observations also suggest that collisions between galaxies may not, as once thought, play a critical role in galaxy evolution.

"Theorists thought that mergers between galaxies were required to initiate this quasar activity, but we now see that quasars can be active in unharassed galaxies," said co-author David Alexander of Durham University in England.

Two telescopes were needed to see the black holes. One is NASA's Spitzer space telescope, which picks up infrared light, and the other is the Chandra telescope, which relays X-ray data.