London, Dec 12 (ANI): A new research has suggested that "nanodiamonds", tiny diamond deposits preserved in meteorites, are not much visible in the Universe because they are hidden within "carbon onions", which are exotic structures made up of concentric layers of graphite.
Since the 1980s, researchers have puzzled over the origin of nanodiamonds, such as the Allende meteorite that landed in Mexico in 1969.
These tiny diamonds make up roughly 3 percent of the carbon in the rocks. That suggests nanodiamonds should abound in clouds of interstellar gas and dust, possibly forged in the fiery blasts of previous supernovae.
But so far, signs of diamonds have only been found in the dusty discs around three young stars.
Strangely, the diamonds are found close to the stars, as opposed to being distributed more evenly in the space around them.
That hints that they were not left over from ancient stellar explosions, but may have formed near the stars, at comparatively low pressures.
Now, researchers led by Miwa Goto of the Max Planck Institute for Astronomy in Heidelberg, Germany, say they have come up with an explanation.
Nanodiamonds may be hidden from view in many places because they form within "carbon onions", exotic structures made up of concentric layers of graphite that can form in dusty material that is blasted with high-energy particles, according to the researchers.
Carbon onions have been used to forge nanodiamonds on Earth. At high temperatures, researchers bombard the layered graphite with electrons.
This knocks atoms out of the onions' outer shells, forcing the remaining atoms in the shells to rearrange and close ranks.
The shells therefore squeeze inwards, eventually creating enough pressure at the centre of the onion to form diamond.
But, conditions must be just right to produce diamonds in carbon onions around stars. A star must eject enough charged particles to turn onions into pressure cells.
Then, in order for astronomers to see the diamonds, one of two conditions must be met.
There must either be a nearby source of X-rays that could slough off the outer layer of the onion to reveal the underlying gems, or the onions themselves must be warm enough - more than 300 degrees Celsius - for the entire carbon onion to be turned into a nanodiamond.
The three stars that boast signs of diamonds are all massive young stars called Herbig Ae/Be stars.
"Notably, they all seem to have the required conditions to create carbon onion diamonds," Goto said. (ANI)