A jet of molecular hydrogen arising from a forming high-mass star

March 7, 2007
Left: Near-infrared image of the M17 silhouette disk, discovered in 2004. The field of view is 27"x27", which roughly corresponds to 60000 AU x 60000 AU (AU stands for astronomical units). Right: Zoom on the central region at six selected wavelengths. The pictures were obtained with SINFONI. Each panel has a field of view of 4.8"x3.6" (i.e. 10560 AU x 7920 AU). While panels (b), (d), and (f) show the densest inner part of the silhouette disk, panels (c) and (e) reveal the H2 jet (individual emission knots are labelled with A, B, and C).

A team of European astronomers offer new evidence that high-mass stars could form in a similar way to low-mass stars, that is, from accretion of gas and dust through a disk surrounding the forming star. Their article, published in Astronomy & Astrophysics, reports the discovery of a jet of molecular hydrogen arising from a forming high-mass star located in the Omega nebula (M17). This detection confirms the hypothesis based on their earlier discovery that this forming high-mass star is surrounded by a large accretion disk.

While astronomers now understand the overall process of low-mass star formation very well, the formation process of massive stars is still very much under debate. Recent astronomical observations suggest that high-mass stars could form through accretion processes, just like low-mass stars do. For instance, in 2004, European astronomers discovered a large accretion disk that probably surrounds a forming high-mass star, in the star-forming region M17, also known as the Omega nebula and located at a distance of about 7000 light years.

Looking again at M17 with the new spectrograph SINFONI at the ESO-VLT, the same European group report discovering a jet of molecular hydrogen (H2) that apparently arises from the forming high-mass star. The picture below illustrates this discovery, which is being published in Astronomy & Astrophysics.

The ejection of material through a jet or an outflow is always linked to accretion of gas and dust, either onto the circumstellar disk or onto the central protostar. The detection of the H2 jet thus provides evidence that ongoing accretion processes occur in the M17 disk. The team also estimates the mass outflow and mass accretion rates, which suggest that a star of high mass is forming within the M17 disk. This is an additional clue that high-mass stars form in a similar way to lower mass stars.

Source: Journal Astronomy & Astrophysics

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