A network of gas filaments in the Orion Nebula

The Orion Nebula
The Orion Nebula

An article published in the journal “Astronomy & Astrophysics” describes a new study of the Orion Nebula. A combination of observations made with the ALMA radio telescope, the 30-meter IRAM telescope and the HAWK-I instrument installed on ESO’s VLT allowed the creation of a unique image of the Orion Nebula. It’s an area of ​​space in which there are various molecular clouds where gas concentrations give life to new stars in processes that can be best studied by putting together the data collected at different electromagnetic frequencies.

The Orion Nebula, also known as Messier 42 or M 42 or NGC 197, is well known because it’s a stellar nursery at around 1,350 light years from the Earth visible even to the naked eye south of the Orion Belt. Inside it, but there’s also one behind it, there are various molecular clouds, particularly interesting for astronomers because it’s within them that there are the conditions for star formation. That’s because they’re interstellar clouds in which hydrogen atoms have reached levels of temperature and density that allow the formation of molecular hydrogen, meaning molecules formed by two hydrogen atoms each, the one from which stars forme.

Because of these characteristics, the Orion Nebula has been studied many times with many different instruments, sometimes by researchers who focused on a single molecular cloud. In this case, a sort of portrait was created that shows a part of it (image ESO/H. Drass/ALMA (ESO/NAOJ/NRAO)/A. Hacar).

putting together 296 data sets collected using the IRAM and ALMA (Atacama Large Millimeter / submillimeter Array) radio telescopes, in red in the image. Observations of the HAWK-I (High Acuity Wide-field K-band Imager) instrument mounted on the VLT (Very Large Telescope) were added, in blue in the image.

These new observations made with the ALMA and IRAM radio telescopes exploited the technique of interferometry to combine signals from a number of widely-separated antennas and create images much more detailed than the ones produced in the past. This makes it possible to see the cold gas filaments that are visible only with instruments such as ALMA, which can detect millimeter wavelengths. There are also many young stars such as the Trapezius cluster, which includes white-blue stars in the upper left corner of the image.

The astronomers who conducted this new study of the Orion Nebula identified a network of 55 filaments, a result useful to better understand their structure and composition. Thanks to the power and sensitivity of the ALMA radio telescope they detected the “signature” of diazenylium, a gas common in interstellar clouds.

The investigation of the structure of the filaments and the fibers that compose them is crucial to understand star formation processes. In the Orion Nebula there’s a dynamic situation with molecular clouds that could be collapsing to give birth to new stars, protostars and fully formed stars. The combined use of various instruments with different characteristics is helping this research.

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