Article Posted on : - Sep 01, 2009

Star formation in distant clusters of galaxies. A file photo

NEW DELHI (BNS): A team of researchers have debunked one long held believe about the formation of stars.

According to a report in Science Daily, since the 1950s astronomers have thought that in a family of new-born stars the ratio of massive stars to lighter ones was always pretty much the same � for instance, that for every star 20 times more massive than the Sun or larger, you�d get 500 stars the mass of the Sun or less.

�This was a really useful idea, unfortunately it seems not to be true,� said team research leader Dr Gerhardt Meurer of Johns Hopkins University.

Stating that the different numbers of stars of different masses at birth is called the �initial mass function� (IMF), they said most of the light we see from galaxies comes from the highest mass stars, while the total mass in stars is dominated by the lower mass stars.

�By measuring the amount of light from a population of stars, and making some corrections for the stars� ages, astronomers can use the IMF to estimate the total mass of that population of stars,� they said.

The team said this ratio of high-mass to low-mass newborn stars differs between galaxies. To arrive at this finding, they used galaxies from the HIPASS Survey (HI Parkes All Sky Survey) done with CSIRO�s Parkes radio telescope.

�All of these galaxies were detected with the Parkes telescope because they contain substantial amounts of neutral hydrogen gas, the raw material for forming stars, and this emits radio waves,� said Dr Baerbel Koribalski, a member of Dr Meurer�s team.

The team found that the ratio, of H-alpha to UV emission, varied from galaxy to galaxy, implying that the IMF also did, at least at its upper end.

�This is complicated work, and we�ve necessarily had to take into account many factors that affect the ratio of H-alpha to UV emission, such as the fact that B stars live much longer than O stars,� Dr Meurer said.

The study now gives a better understanding of other recently observed phenomena that have been puzzling astronomers, such as variation of the ratio of H-alpha to ultraviolet light as a function of radius within some galaxies.