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03/27/2013

How the biggest stars are born: U of T research offers new clues

Stars should not be able to grow any larger than eight times the size of our own sun. Yet they do: astronomers have observed stars larger than this, leading to the puzzling question of how they have managed to achieve such an abnormally high mass.

In new research announced Wednesday, scientists at the University of Toronto have discovered clues as to how these high-mass stars are created: by having the luck to be born in a region where they can feed off the gases of other, older high mass stars.

Stars are born in clouds of galactic dust. They grow by feeding off gas, but at a certain size, they begin to push gas away. That's why scientists calculated a theoretical limit to the size of newborn stars: at a certain point they drive away their own food source.

The U of T researchers -- led by Alana Rivera-Ingraham, who was a graduate student at U of T when she led the study and is now at the Institut de Recherche en Astrophysique et Planétologie in France -- used data from the Herschel Space Observatory, a telescope launched by the European Space Agency three years ago. The telescope records high-resolution images in the far-infrared spectrum, light that is invisible to the naked eye.

Rivera-Ingraham and the team observed one area 6,500 light years away from Earth called Westerhout 3, and noticed that one particularly dense part of the region was surrounded by a number of high-mass stars.

They theorize that as a young star becomes large enough and starts to push gas away, the older, very large stars push the gas back towards it, allowing it to grow to an abnormally large size.

The research is published in April in The Astrophysical Journal and was supported by the Canadian Space Agency and NSERC.

 Kate Allen is the Star's science and technology reporter. Find her on Twitter at @katecallen.

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