These images show the edge of the vast molecular cloud that lies behind the Orion Nebula, 1400 light-years from Earth. The image of the left shows a wide-field view of the region, as seen with the HAWK-I instrument, installed at ESO’s Very Large Telescope. A small region is highlighted with a white rectangle, and the rightmost image shows that region in stunning fiery detail, observed with the Atacama Large Millimeter/submillimeter Array (ALMA) and the IRAM 30m telescope.

As well as producing beautiful images, molecular clouds are of great interest to astronomers. The clouds are stellar nurseries and at their edge atoms react and form molecules by key astrochemical processes. With the ALMA observations scientists were able to resolve this transition from atomic to molecular gas at the border of the Orion molecular cloud. As Orion is the nearest massive star-forming region it is the ideal target to find out more about these astrochemical processes, and it also offers the possibility to study the interactions of newly formed stars with their surroundings in detail.

Both observations show that this fascinating astrochemical transition from atomic to molecular gas happens in a highly dynamic environment. ALMA’s view of the nebula particularly resembles the dark clouds of a huge upcoming storm in Earth’s atmosphere.

These observation results were published online as Goicoechea et al. “Compression and ablation of the photo-irradiated molecular cloud the Orion Bar” by the journal Nature on August 10, 2016.

Credit: ESO/Goicoechea et al.; ALMA (ESO/NAOJ/NRAO)