Complex Organic Molecules tracing shocks along the outflow cavity in the high-mass protostar IRAS 20126+4104.

We report on subarcsecond observations of complex organic molecules (COMs) in the high-mass protostar IRAS 20126+4104 with the Plateau de Bure Interferometer in its most extended configurations. In addition to the simple molecules SO, HNCO and H213CO, we detect emission from CH3CN, CH3OH, HCOOH, HCOOCH3, CH3OCH3, CH3CH2CN, CH3COCH3, NH2CN, and (CH2OH)2. SO and HNCO present a X-shaped morphology consistent with tracing the outflow cavity walls. Most of the COMs have their peak emission at the putative position of the protostar, but also show an extension towards the south(east), coinciding with an H2 knot from the jet at about 800-1000 au from the protostar. This is especially clear in the case of H213CO and CH3OCH3. We fitted the spectra at representative positions for the disc and the outflow, and found that the abundances of most COMs are comparable at both positions, suggesting that COMs are enhanced in shocks as a result of the passage of the outflow. By coupling a parametric shock model to a large gas-grain chemical network including COMs, we find that the observed COMs should survive in the gas phase for ∼ 2000 yr, comparable to the shock lifetime estimated from the water masers at the outflow position. Overall, our data indicate that COMs in IRAS 20126+4104 may arise not only from the disc, but also from dense and hot regions associated with the outflow.

The critical role of disks in the formation of high-mass stars.

Although massive stars (commonly defined as those in excess of about eight solar masses, or with initial luminosities of a thousand times the solar luminosity or more) have an enormous impact on the galactic environment, how they form has been a mystery. The solution probably involves the existence of accretion disks. Rotational motions have been found in the gas surrounding young high-mass stars, which suggests that non-spherical accretion could be the fundamental ingredient of the massive-star formation recipe.

Infall of gas as the formation mechanism of stars up to 20 times more massive than the Sun.

Theory predicts and observations confirm that low-mass stars (like the Sun) in their early life grow by accreting gas from the surrounding material. But for stars approximately 10 times more massive than the Sun (approximately 10M(o)), the powerful stellar radiation is expected to inhibit accretion and thus limit the growth of their mass. Clearly, stars with masses >10M(o) exist, so there must be a way for them to form. The problem may be solved by non-spherical accretion, which allows some of the stellar photons to escape along the symmetry axis where the density is lower. The recent detection of rotating disks and toroids around very young massive stars has lent support to the idea that high-mass ( > 8M(o)) stars could form in this way. Here we report observations of an ammonia line towards a high-mass star forming region. We conclude that the gas is falling inwards towards a very young star of approximately 20M(o), in line with theoretical predictions of non-spherical accretion.