Cosmic Crumbs 'May Have The Numbers'

December 25, 1997

Tiny 'dwarf' galaxies may dominate the Universe, CSIRO astronomers suggest. After analysing only 2% of the data from a pioneering survey with the Parkes radio telescope, the astronomers have found far more dwarf galaxies than they expected.

A hundredth the size of our Galaxy, dwarfs may be 'crumbs' left over when bigger galaxies formed.

Dwarfs are faint and hard to find. They and other faint galaxies are turning up as the Parkes telescope hunts for hydrogen gas, the raw material of stars, with a special new instrument.

"Galaxies like our own - the so-called 'normal' galaxies - aren't normal at all," said CSIRO's Dr Lister Staveley-Smith, the project's leader. "In fact they are vastly outnumbered by the dwarfs."

Dwarf galaxies are more evenly spread through space than the big bright ones.

"The bright stuff is the just tip of the iceberg," said Dr Staveley-Smith. "The dwarfs show us much better how the mass of the Universe, especially the invisible 'dark matter', is distributed."

'Dark matter' may make up 90% of the stuff in the Universe.

"The dwarfs may also have the lion's share of the dark matter," said Dr Staveley-Smith. "They seem to have most of the hydrogen gas, and some astronomers think that's linked to the dark matter."

In a related search the Parkes telescope has found more than 100 galaxies hidden behind the stars and dust of the Milky Way. They cannot be seen by ordinary optical (light) telescopes.

Dr Staveley-Smith likened the search for these hidden galaxies to filling in a jigsaw puzzle with a large section missing.

"Structures are gradually appearing through the murk of the Milky Way," he said. "Long lines and sheets of galaxies."

"These are joining up with structures we already knew about," he said.

The astronomers are trying to pin down "the Great Attractor". This is supposed to be a concentration of galaxies right behind the Milky Way whose gravity is dragging nearby galaxies towards it.

"People have argued for decades about whether the Great Attractor is real or not," said Dr Staveley-Smith. "We will settle the question one way or the other."

The searches for faint and hidden galaxies started in March this year.They rely on a new 'multibeam' instrument on the Parkes telescope. Like the wide-angle lens of a camera, this increases the telescope's field of view 13-fold. Developed by CSIRO, it is the most powerful instrument of its kind in the world.

The searches are being done by CSIRO in collaboration with the Universities of Sydney, Western Sydney and Melbourne, Mt Stromlo and Siding Spring Observatories, and overseas institutions.
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CSIRO Australia

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