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When young stars play hide-and-seek

Probing stellar nurseries in the Carina nebula

Munich, 09/19/2011

Lone stars are relatively rare. Stars are gregarious, and tend to occur in clusters or so-called associations. This suggests that pre-existing massive stars play a part in the creation of new stars, but the nature of this role is not entirely clear. LMU astrophysicist Professor Thomas Preibisch leads a research group, based at the LMU Observatory, devoted to elucidating the link between young stars and stellar evolution in their vicinity. The goal is to understand the interaction between young, hot stars and the clouds of gas and dust in which new stars are born. They have now studied the radiation emitted by stars in the Carina nebula at multiple wavelengths, including the X-ray region, and the near and far infrared. “This nebula can provide us with detailed information on the process of star formation, because it contains a particularly high concentration of massive stars,” says Preibisch. “In our latest study we identified and characterized more than 14,000 young stars in the Carina nebula. The next step is to have a closer look at the structure of the clouds of gas and dust that provide the building material for new stars.” The new results appeared in a special supplementary issue of the Astrophysical Journal and were the subject of a commentary in Nature.

Stars prefer company to loneliness. They are most likely to form in large clusters that may contain more than 100,000 stellar objects. The larger the number of stars in such an association, the more massive its members tend to be. “The overall luminosity and, in particular, the flux of ultraviolet radiation produced by a star increases rapidly with its mass,” says Professor Thomas Preibisch of LMU Munich. “As a result, the interaction between young stars and the clouds of gas and dust in which they originate is dominated by the contributions of the most massive stars.”

The exceptionally bright nebula in the constellation Carina, which is located in the Southern sky, lies some 7,500 light-years from Earth. The nebula is home to a large population of very massive stars, i.e., objects with masses more than 50 times that of the Sun. Moreover, the levels of UV radiation emitted by such objects are several million times higher than that produced by the Sun. The huge streams of energy discharged by these stars slam into nearby clouds made up of gas and dust, either ripping them apart – or sowing the seeds of new stars. For if a cloud is located at least a few light years away, the pressure exerted by the UV radiation and the impact of high-energy particles in the stellar wind will compress the material in the cloud sufficiently to initiate star formation.

"Which of these two effects is the dominant one is the subject of intense debate among astronomers,” says Preibisch. “The Carina nebula is ideally suited for answering questions like this, because here it is possible to investigate the influence, or feedback, of giant stars on the clouds in their vicinity in great detail.” However, this does not mean that teasing out the answers will be easy. In optical images of the Carina nebula, it is quite difficult to identify young stars, because most are obscured by opaque clouds of dust or their light is swamped by the glow given off when hydrogen ions in the nebula recombine.

That is why Preibisch and his coworkers focused on the energetic X-rays that young stars send out. As part of the Chandra Carina Complex Project, a collaborative undertaking involving European and American colleagues which is led by Leisa Townsley (Pennsylvania State University), the LMU astronomers were able to study the nebula in detail with the aid of NASA’s X-ray satellite Chandra. “Using an exposure time lasting all of 17 days, we obtained an X-ray image in which we were able to distinguish 14,368 point sources”, says Preibisch. Near-infrared images of the same region, taken with the Very Large Telescope (8 m in diameter) at the European Southern Observatory in Chile, enabled the team to characterize the population of young stars in detail.

In the next stage of the project, attention will turn to the structure of the clouds near these young stars. Preibisch and his team will use Herschel, the European Space Agency’s infrared satellite, to assemble high-resolution images of the Carina nebula. “With the help of these observations in the infrared and other data for other spectral regions, we hope to put together a comprehensive picture of the structure of the clouds in the Carina star-forming region and the physical processes going on within them,” he says. “Once again, we will focus on the interactions between massive young stars and the clouds that surround them.” (suwe/PH)

Publications:
Near-Infrared Properties of the X-Ray-Emitting Young Stellar Objects in the Carina Nebula
Thomas Preibisch et.al.
The Astrophysical Journal, Supplement Series, May 2011
http://dx.doi.org/10.1088/0067-0049/194/1/10

A census of the Carina Complex
Theodore R. Gull
Nature 475:460-461, 28. July 2011
http://www.nature.com/nature/journal/v475/n7357/full/475460a.html

An Introduction to the Chandra Carina Complex Project
Leisa K. Townsley et.al.
The Astrophysical Journal, Supplement Series, May 2011
http://dx.doi.org/10.1088/0067-0049/194/1/1

Deep wide-field near-infrared survey of the Carina Nebula
Thomas Preibisch et al.
Astronomy & Astrophysics, Juni 2011
http://dx.doi.org/10.1051/0004-6361/201116781

Contact:
Professor Thomas Preibisch
LMU Observatory Munich
Phone: 089 / 2180 – 6016
Fax: 089 / 2180 –  6003
Email: preibisch@usm.uni-muenchen.de
Web: www.usm.uni-muenchen.de/people/preibisch

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