News in Science

Dust clouds reveal how quickly stars form

Starburst A new and more accurate way of predicting star birth rates, one of the most fundamental processes in the universe, has been developed by researchers.

The study reported in the journal Science, will help astronomers researching galactic evolution, and provide a first step in defining where new stars and planets are likely to form.

Stars are born deep inside giant molecular clouds which can be hundreds of light years wide, and spread across a galaxy.

Star birth takes place when the cold gas and dust in these clouds reaches a high enough density.

Astronomers currently determine star formation rates by estimating the density distribution of gas in each cloud.

However, these estimates are based on theoretical 3D models of what are actually 2D images of clouds.

The new research, which included Dr Christoph Federrath of Melbourne's Monash University, provides a way of estimating the true 3D structure of these clouds.

"For the first time we can directly compare predictions of star formations theories and test them with real data," says Federrath.

Federrath and colleagues at the Max-Planck Institute for Astronomy in Germany, looked at 16 molecular clouds within 1500 light years of Earth, which were actively forming stars.

The researchers measured how infrared light from the background stars dimmed as it passed through the dust clouds.

"The key to measuring the amount of gas and dust between us and each of those stars, is knowing the intrinsic luminosity [brightness] of the star," says Federrath.

By measuring the drop in infrared light, the researchers were able to reconstruct the density of the material in the clouds.

Critical mass

After plugging their calculated density distributions into the existing models, Federrath and colleagues were able to identify the point at which star formation would occur.

"We found the critical density above which stars form is about 5000 hydrogen molecules per cubic centimetre," says Federrath.

"This density figure had been predicted in theory for some years, but now we can reconstruct the estimated 3D structure of these clouds and test the theory."

The next step will be trying to determine how massive a star is likely to be when it forms at a specific location inside a cloud, and how many stars are likely to form there.

"We are at the stage where we can predict the rate at which this gas will form some stars, but we can't really say how many stars and with what mass," says Federrath. "The next step is to get their numbers and masses right."