Astronomers believe they have uncovered the mystery surrounding ancient black holes, which rapidly grew into supermassive objects around 12 billion years ago.
An international team of researchers have identified a "food source" that fuels these enigmatic phenomena made of dense matter at the heart of galaxies.
In a study published in The Astrophysical Journal, the team reported that the so-called "black hole food" was made up of reservoirs of interstellar gas and dust that surrounds galaxies.
This fuel allowed these cosmic monsters to grow rapidly at a time when the universe was still young.
The scientists believe their findings add "a fundamental piece to the puzzle" on how cosmic structures, featuring galaxy clusters and voids, were formed.
Dr Emanuele Paolo Farina, of the Max Planck Institute for Astronomy in Germany, said: "The presence of these early monsters, with masses several billion times the mass of our Sun, is a big mystery.
"We are now able to demonstrate, for the first time, that primordial galaxies do have enough food in their environments to sustain both the growth of supermassive black holes and vigorous star formation."
The astronomers used the European Southern Observatory's Very Large Telescope, including an on-board instrument known as Muse, to gather data on the ancient black holes.
They surveyed 31 quasars - extremely bright nuclei in active galaxies.
The astronomers found 12 of those quasars were surrounded by enormous reservoirs made up of cool, dense hydrogen gas.
These gas halos were tightly bound to the galaxies which, according to the researchers, provided "the perfect food source" to sustain the growth of supermassive black holes.
Dr Farina said: "In a matter of a few hours per target, we were able to delve into the surroundings of the most massive and voracious black holes present in the young universe.
"While quasars are bright, the gas reservoirs around them are much harder to observe.
"But Muse could detect the faint glow of the hydrogen gas in the halos, allowing astronomers to finally reveal the food stashes that power supermassive black holes in the early universe."
