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How do massive stars form?

June 2009




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The early stages of the process by which massive stars are formed are governed by the interstellar magnetic fields, in a process similar to the formation of stars like the Sun. A paper on the subject has recently been published in Science, co-authored by the researcher Robert Estalella of the Department of Astronomy and Meteorology. Massive stars (stars that are more massive than 8 solar masses) represent only 1% of our galaxy; however, they dominate the appearance and evolution of the interstellar medium and are responsible for the production of heavy elements. Stars form within molecular clouds, and one of the biggest unknowns has been the role of magnetic fields during the collapse of a molecular cloud. Up until now, the assumption was that turbulence regulates the formation of massive stars.



The scientific team, headed by astronomer Josep Miquel Girart of the Institute of Space Sciences (CSIC-IEEC), used the Submillimeter Array (SMA), located near the summit of Mauna Kea in Hawaii at an altitude of 4,080 metres, in order to analyse an extremely dense, hot gas and dust cloud containing very young massive stars. The cloud is located 23,000 light years from Earth in the Serpens constellation.
The team’s observations were made at submillimetre wavelengths, which allowed detection of the physical properties of the molecular cloud G31.41+0.31 and, in particular, its magnetic field. «From the dust polarized emission detected with the SMA, we derived the structures of the interstellar magnetic field that threads the cloud. We found that it has an hourglass shape, similar to what we found three years ago around a stellar embryo (a future Sun). However, G31.41+0.31 is 20 times larger, 200 times more massive and one hundred thousand times brighter», says the CSIC researcher. «In addition, we found that the magnetic field is the main agent controlling the collapse of the cloud. In fact, we found that its effect is greater than that of turbulence, contrary to what we originally thought», explains expert Maria Teresa Beltrán of the Arcetri Observatory (Italy).
On the future evolution of the cloud, Robert Estalella adds «There are still many questions to answer. But, in our opinion, this massive cloud is very likely to form hundreds of stars, most with characteristics similar to the Sun, although some will be very massive. And how this happens is not clear».
The team of Catalan researchers worked in collaboration with Qizhou Zhang of the Harvard-Smithsonian Centre for Astrophysics, and Ramprasad Rao of the Institute of Astronomy and Astrophysics.


 
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Last update: 22.06.2009