Washington: Astronomers have discovered the oldest and most distant carbon in the universe, but they claim that there is not enough of it to support the theories of how the universe lit up.
In the early universe, a dark pervasive fog of neutral hydrogen gas lurked everywhere. Planetary scientists believe this fog cleared when the first stars formed to emit light.
There is a close connection between the amount of light and carbon produced in stars. But adding up all the 13-billion-year-old carbon detected, an international team came to the conclusion the amount of carbon, and therefore the number of massive stars, was insufficient to lift the fog.
"So light must come from somewhere else, perhaps an unknown population of quasars, or stars that lock-up more of their carbon, or carbon hidden in unobserved states," Dr Emma Ryan-Weber of Swinburne University of Technology, who led the team, said.
When the universe began with the Big Bang only hydrogen and helium existed. The astronomers know the carbon they have discovered is old because it was detected in infrared wavelength rather than in the ultra-violet as on Earth.
The universe has expanded so much since the Big Bang that the wavelength of the light from carbon atoms has stretched from 155 to 1085 nanometres by the time it reaches the Earth.
Even though astronomers have been observing intergalactic carbon for many years, no-one had tried to detect it in the early Universe, because this involved looking in the near-infra-red.
Observations in the near-infrared are challenging because of the interference of intense 'airglow' lines in the night sky.
The details surrounding the end of the dark Universe, a process know as re-ionisation, are among the last mysteries of modern cosmology.
Astronomers have yet to discover when the starlight from the first galaxies lit up the Universe, ionising the surrounding neutral hydrogen gas. And they don't know how massive these galaxies were, or whether they contained the same types of stars as we see today.
Even measurements suggesting the greatest number of galaxies in the early Universe could only lead to just enough light to lift the fog if the conditions are tweaked in the right way. Emma's survey of intergalactic carbon in the early universe provides a completely independent measure of the amount of starlight.
"A lot more starlight is needed to lift the fog. It's like going from a visibility of a metre to being able to see a kilometre down the road," Ryan-Weber said.