19 September 2005

Astrophysicists have long debated the existence of "dark galaxies" – giant clouds of hydrogen and dark matter, which are the building blocks of stars – that fail to form stars.

But a new study by a University of Queensland researcher has gone some way to disproving the dark galaxy theory.

Marianne Doyle, a postgraduate student with UQ’s Astrophysics Research Group and part of the international HI Parkes All Sky Survey (HIPASS) collaboration, has recently completed a catalogue of the whole of the southern sky and has failed to find any evidence of dark galaxies.

“There should be loads of them but we didn’t find any,” she said.

In 1976 astrophysicist Mike Disney predicted there should be a large population of previously undetected very faint galaxies, some being dark galaxies that do not form stars.

To date all but one dark galaxy claim have been proven incorrect, with a possible dark galaxy find in the Virgo cluster still being hotly debated.

Ms Doyle’s research, published recently in Monthly Notices of the Royal Astronomical Society, was part of a radio/optical catalogue she produced as part of her PhD.

Ms Doyle spent two-and-a-half years searching radio data obtained by CSIRO`s Parkes radio telescope and cross-checking it with optical data from the Anglo-Australian Observatory`s UK Schmidt Telescope at Siding Spring Observatory in New South Wales.

The radio data (from the HIPASS catalogue) revealed clouds of hydrogen in space, while the optical data (from the SuperCOSMOS surveys and 6dF Galaxy Survey) showed the positions of the galaxies that had formed stars.

"All the hydrogen clouds seem to be associated with galaxies that have stars," Ms Doyle said.

While not ending the debate about whether dark galaxies exist or not, she said the research would add weight to those who argue against the theory.

“I would have loved to have found one but it didn’t happen,” she said.

Ms Doyle said her research also proved valuable by providing a catalogue of the whole of the southern sky that contained not just bright optical galaxies but fainter galaxies detected using the CSIRO’s Parkes radio telescope.

Ms Doyle came to the world of astrophysics late as a mature-age student, but her passion for the science was sparked as a child when she first wondered what was up in the night sky.

“I always wanted to be an astronomer since I was six, but I never did much about it,” she said.

That was until she spent six weeks on crutches at 36, after chasing her son’s kite that was heading towards a tree.

“When I broke my leg, I thought I’d go insane if I didn’t do something and that was when I thought about studying again.”

“So thanks to that $2 kite, which I did save, I’m doing what I’ve always wanted to do – study the stars.”

Media inquiries: Marianne Doyle (07 3346 9727, Email: mtdoyle@physics.uq.edu.au or visit: http://www.physics.uq.edu.au/people/doyle/) or Andrew Dunne at UQ Communications (07 3365 2802).