Astronomers glimpse birth of mega-stars

Using a CSIRO radio telescope, astronomers have caught an enormous cloud of cosmic gas and dust in the process of collapsing in on itself. They hope the discovery could help establish how massive stars form.

Dr Peter Barnes from the University of Florida says astronomers have a good grasp of how stars such as our sun form from clouds of gas and dust. But for heavier stars – ten times the mass of the sun or more – they are still largely in the dark, despite years of work.

“Astronomers are still debating the physical processes that can generate these big stars,” says Barnes.

“Massive stars are rare, making up only a few per cent of all stars, and they will only form in significant numbers when really massive clouds of gas collapse, creating hundreds of stars of different masses. Smaller gas clouds are not likely to make big stars.”

Most regions in space where massive stars are forming are well over 1,000 light-years away, making them hard to spot.

But using CSIRO’s ‘Mopra’ radio telescope – a 22m dish near Coonabarabran, New South Wales – the team discovered a massive cloud made mostly of hydrogen gas and dust, three or more light-years across, that is collapsing in on itself and will probably form a huge cluster of stars.

Dr Stuart Ryder of the Anglo-Australian Observatory said the discovery was made during a survey of more than 200 gas clouds. Called BYF73, it’s about 8,000 light years away, in the constellation of Carina in the Southern sky.

“With clouds like this we can test theories of massive star cluster formation in great detail,” says Ryder.

Evidence for ‘infalling’ gas came from the radio telescope’s detection of two kinds of molecules in the cloud – HCO+ and H13CO+. The spectral lines from the HCO+ molecules in particular showed the gas had a velocity and temperature pattern that indicated collapse.

The research team calculates that the gas is falling in at the rate of about three per cent of the Sun’s mass every year – one of the highest rates known.

Follow-up infrared observations made with the 3.9-m Anglo-Australian Telescope showed signs of massive young stars that have already formed right at the centre of the gas clump, and new stars forming.

Star-formation in the cloud also showed up in archival data from the Spitzer and MSX spacecraft, which observe in the mid-infrared.