Any dictionary will tell you that a galaxy is a vast collection of stars,
floating deep in space. But this definition may need revision following new
research by an ANU graduate student who has discovered galaxies that consist
mostly of gas, rather than stars.

In research to be presented to the General Assembly of the International
Astronomical Union in Sydney today, Brad Warren will reveal his discovery of
twenty gassy galaxies, which have very few stars.

"When you look for gas [in these galaxies] the signal just booms in," Mr Warren
said. "But when you look for stars, all you see is a barely recognisable smudge."

The galaxies are vast discs of hydrogen, tens of thousands of light years
across, weighing more than a billion suns, with a tiny number of barely visible
stars in their centre.

For an unknown reason, they have not transformed their rich source of hydrogen
gas into masses of stars like their brilliant, twinkling counterparts.

"Hydrogen is the most common element in the Universe and it forms the building
blocks for stars," Mr Warren said.

"Most galaxies, like our own Milky Way, have transformed most of their gas but
the galaxies we have discovered have held back and we are not sure why.

"Discovering this missing link will give us important insights into how, when
and why galaxies, such as our own, formed."

Although the existence of gassy galaxies has been documented in the past, it is
the first time they have been discovered with such prominent discrepancies
between the amount of hydrogen gas and stars.

"This research throws up a further challenge in the ongoing quest to discover
the secrets of the Universe," Mr Warren said.

Mr Warren, from the Research School of Astronomy and Astrophysics, collaborated
with fellow ANU researcher, Dr Helmut Jerjen, and Dr Barbel Koribalski, from the
CSIRO’s Australia Telescope National facility.

The team used three of Australia’s most powerful telescopes for their research
— the Parkes Radio Telescope; the Australia Telescope Compact Array near
Narrabri and the University’s 2.3 metre telescope at Siding Spring Observatory,
Coonabarabran.