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New star formation 'recipe' uses dust scattering as an ingredient

Elizabeth Howell, News Writer
Apr 10, 2014, 7:00 UTC

Sen—Building a star takes far fewer gas molecules than previously calculated, according to a new model based on observations of molecular clouds around our own Milky Way. If confirmed by other teams, the result could give scientists a better understanding of how stars form.

The new technique gets around the problem of having few observations to make the calculations. Historically speaking, most of our understanding of star formation comes from counting stars in nearby clouds. At distances beyond 1,500 light years, however, these individuals become impossible to see.

Instead of fighting against the clouds of gas and dust that surround and dim the young light of stars, the new technique takes advantage of the situation. Astrophysicists examined how the stars' electromagnetic radiation is scattered, which showed them how dense the region was. Next, the scientists put the density calculation into a standard star-formation calculator, yielding the new result.

Milky Way

The Pipe Nebula (left) and the Rho Ophiuchi cloud backdropped by the Milky Way, in which these are located. The maps are three-dimension reconstructions of cloud structures. Image credit: Background: ESO/S. Guisard / Column-density maps: J. Kainulainen, MPIA

What they found was that star formation can only take place in regions with a "critical density" of more than 5,000 hydrogen molecules per cubic centimeter. This is quite a bit lower than other estimates, and the researchers said the reason for the discrepancy is not yet known.

"This is the first time anyone has determined a critical density for forming stars from observations of cloud structure," stated Jouni Kainulainen, an astronomer from the Max Planck Institute for Astronomy in Germany who led the research. 

"Theories of star formation have long predicted the importance of such a critical density. But our reconstruction technique is the first to allow astronomers to deduce the density structure of these clouds—and to confront star formation theories with observational data."

Star formation

A computer simulation of how stars form in a gas cloud. Star formation is marked in circles, and brighter colours are meant to represent more massive stars. Credit: C. Federrath, Monash University

The calculations rely on a combination of observation and modelling to arrive at the data. This means that as astronomers use new tools to examine the Universe, what we believe is the threshold for star formation could change if better information comes through.

For this reason, the astronomers are pushing for the use of a new telescope that is designed to look at stars being born. Called the Atacama Large Millimeter/sub-millimeter Array (ALMA), the Chilean set of 66 telescopes just reached its full complement of receivers in the last year. 

As ALMA peers at distant gas clouds and results from the telescope become widely available, the astronomers said that it would be possible to estimate star formation based on that information.

"With our technique, we're able to say: Show us your data, and we will tell you how many stars your cloud is forming right now," stated Thomas Henning, director at the Max Planck Institute for Astronomy and co-author of the study.

The study was published today (10 April) in the journal Science.