There’s activity in the molecular cloud behind the Orion Nebula

The molecular cloud behind the Orion Nebula seen by HAWK-I (left) and ALMA (right) (Image ESO/Goicoechea et al.)
The molecular cloud behind the Orion Nebula seen by HAWK-I (left) and ALMA (right) (Image ESO/Goicoechea et al.)

An article published in the journal “Nature” describes a research about the molecular cloud located behind the Orion Nebula. A group of researchers used the HAWK-I instrument installed on ESO’s Very Large Telescope (VLT) and the ALMA radio telescope, both ESO’s, to look at key moments of astrochemical phenomena, meaning the chemical reactions that take place in space and in this case in that area and one day will lead to the birth of new stars.

Molecular clouds are interstellar gas clouds in which hydrogen atoms reached levels of temperature and density such as to allow the formation of molecular hydrogen, meaning molecules consisting of two hydrogen atoms each. They’re particularly interesting for astronomers because in those clouds there are the conditions for the formation of stars.

The Orion Nebula, also known as Messier 42 or M 42 or NGC 197, is well known because it’s visible even to the naked eye in the south of Orion’s Belt. Behind it, almost 1400 light years from Earth, there’s a large molecular cloud, the closest star-forming region to Earth and therefore subject to various observations with increasingly sophisticated tools.

In this case, the researchers used both the HAWK-I (High Acuity Wide-field K-band Imager) instrument mounted on the VLT and the ALMA (Atacama Large Millimeter/submillimeter Array) radio telescope to observe in particular an edge of that molecular cloud. HAWK-I allowed to obtain wide field images of the cloud while ALMA’s sensitivity allowed to obtain the details of the transition from atomic to molecular gas in smaller regions.

The environment of the molecular clouds is dynamic with the hydrogen atoms which combine into molecules but especially when those molecules start coalescing. In the clouds there are also traces of other heavy elements generally coming from supernovae sometimes distant where they were created and then pushed into space.

According to the researchers, the edge of the molecular cloud behind the Orion Nebula was compressed by a high pressure wave that is moving into the cloud. It’s evidence of the fact that the dynamical and non-equilibrium effects are important for the evolution of the cloud.

These are the very early stages of evolution of an interstellar cloud that will lead to the birth of new stars. The observations of these events are a long-term task to say the least since it may take a few million years to see the first light of a newly born star.

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