|The Big Bang theory is being challenged|
|March 24th 1999
An Australian-led team of astronomers has challenged conventional Big Bang theory by finding that large numbers of stars may be living unseen in the space between the galaxies.
Team leader Professor Ken Freeman of the Australian National University will describe the finding tomorrow [24 March] at a meeting in Sydney hosted by CSIRO's Australia Telescope National Facility and the Anglo-Australian Observatory.
"All these extra stars mean that there is too much normal ('baryonic') matter in the Universe to fit well with the current version of the Big Bang theory," Professor Freeman says.
Galaxies live in great clusters, like swarms of bees. The astronomers have been hunting for stray stars in two clusters, Virgo and Fornax.
"Galaxies jostle and harass each other, and you'd expect that a lot of stars get flung out of them," says Dr David Malin of the Anglo-Australian Observatory, another member of the observing team. "But although people looked for these 'lost sheep' before, they didn't find them. The amount of space between the galaxies is so big that the stars are very spread out and therefore look quite dim overall."
"Our approach, which is new, is to look for stars near the end of their lives, when for a short time they shed a lot of their material," says Professor Freeman.
"When they're in this so-called 'planetary nebula' phase you can detect them as individual objects up to 50 million light-years away - the oxygen they contain puts out a very distinctive signal."
"We and another group have between us found more than 160 of these objects. From that, we can work out how many ordinary stars there are in the underlying population," he says.
"There may be as many stars living out in the 'wilderness' of intergalactic space as live in the 'cities' - the galaxies."
Having all these extra stars is a problem.
"Conventional Big Bang theory tells us how much of the light chemical elements, such as helium and deuterium, were formed when the Universe began. The amount of these elements we can see tells us how much baryonic matter (ordinary matter, made of protons and neutrons) there is in the Universe," explains Professor Freeman.
"Even before this finding, it looked like we might have had a bit too much baryonic matter in the Universe to fit well with the theory. It was a borderline problem. But the extra stars we've found make the problem even worse."
Where the intra-cluster stars come from is unclear.
"Perhaps they were formed far out in space, at the same time the galaxies were forming. But I think it's more likely they were ripped from their home galaxies as the galaxies 'rubbed shoulders'," Professor Freeman says.
"We are testing this idea by measuring the velocities of the stray stars we've detected. That will tell us if those stars are spread out in very faint long streamers behind the galaxies."
Could these intra-cluster stars account for some of the Universe's 'missing mass' - dark stuff that shows up through its gravitational effects? No. "The stars don't have enough mass to even 'touch the sides' of that problem," says Professor Freeman.
The overall study was made with the Anglo-Australian Telescope in New South Wales, the New Technology Telescope of the European Southern Observatory in Chile, and the William Herschel Telescope in the Canary Islands. The velocities of the individual stars are being measured with the two-degree-field (2dF) instrument on the Anglo-Australian Telescope, which is the best instrument in the world for doing this work.