Scientists are trying to work out what
brought the Universe's 'dark ages' to an
end.
Image: iStockphoto

During a mysterious era, about a billion years after it is estimated to have formed, the universe was flooded with light. A veil of neutral hydrogen gas tore apart and the brilliance of starlight shone through.

Swinburne University of Technology astronomer Dr Emma Ryan-Weber is fascinated by this epic time, the ending of the so-called ‘dark ages’ of the cosmos, and is determined to unravel one of the enduring mysteries of modern astronomy: what brought it about?

In her latest investigations with Professor Max Pettini and Berkeley Zych of Cambridge University, UK, and Professor Piero Madau at the University of California, Santa Cruz, the team has already uncovered part of the explanation – and is now in hot pursuit of the remainder.

The answer has to do with carbon, which, besides being the curse of the 21st century for humans, is also the burnt fuel of the stars, reaching right back to their first generation which formed after the Big Bang. In carbon lurks the secret of universal illumination.

By studying the amount of carbon in the cosmos, astronomers can infer how much starlight there has ever been. But seeing loose carbon atoms floating around in the immensity of space 12 billion years ago or more is not easy. To begin with it requires two of the greatest instruments ever built: the Very Large Telescope of the European Southern Observatory atop a desert mountain in Chile; and the immense 10-metre eye of the Keck telescope in Hawaii. Astronomers queue up for years for a few hours on either.

Coupled with a spectrograph, which reads the elements that comprise the universe like the lines in a barcode, carbon can be seen – but only with difficulty because hydroxyl, a substance in Earth’s atmosphere, obscures it in the spectrum. Dr Ryan-Weber and Professor Pettini must, literally, peer between the bars of earthly hydroxyl to glimpse the distant carbon in the heavens.

“Carbon is normally shed into space when a very large star goes supernova, blasting its contents across the universe. After that, it never goes away. Our idea was that if we measured the amount of carbon visible in this very early era, we could maybe work out whether there was enough energy being shed by the early stars to turn the fog of hydrogen obscuring the early universe transparent and end the darkness,” Dr Ryan-Weber explains. The idea is that at some point sufficient stellar energy was generated to turn the neutral hydrogen into an excited (ionised) state, causing its atoms to shed an electron – and allow light to pass through.

“A very great deal of starlight is needed to lift the fog. It’s like going from a visibility of one metre to being able to see a kilometre down the road,” she adds. The carbon is an indicator of how much light was being generated.

The answer the team has recently found has only caused the mystery of what lit up the early universe to deepen. In observations earlier this year they measured about one-fifth of the carbon reckoned necessary for the ‘dark ages’ to end and light to shine out everywhere. Where was the rest of the carbon?

“We concluded there must be a large, unseen carbon source accounting for as much as 80 per cent of the energy necessary to clarify the hydrogen ‘fog’,” she says. Some of this carbon may exist in a state or states still undetected by telescopes, or additional energy may come from quasars – compact, ultra-energetic objects at the heart of certain galaxies probably powered by black holes – which do not produce carbon.

Thanks to the Swinburne Centre for Astrophysics and Supercomputing’s special access to the world’s largest telescope, the Keck, Dr Ryan-Weber is booked for three nights’ observing around the time of the New Year, when she hopes to track the missing carbon to its source and throw new light on what ended the ‘dark ages’. “We’ll be looking for carbon in another state,” she says.

The detail of what happened during the ‘dark ages’ is one of the remaining frontiers of modern astronomy still to be explored but, with luck and skill, her team’s research will help roll back the curtain and let us see into our remotest past.

Dr Ryan-Weber is one of the rising generation of young astronomers being nurtured at Swinburne. “I adore it,” she says. “I’ve been in love with astronomy ever since my dad took me to see Halley’s Comet when I was 10 years old.” Although she has since witnessed many more astonishing celestial phenomena, she has never lost the enduring thrill that a new insight into our wondrous universe bestows.