Known for sheltering the Horse’s Head and Flame nebulae the Orion B nebula is a huge reservoir of interstellar matter, , made up of gas and dust, whose total mass is on the order of 70 000 times that of the Sun.
Stars are born in the centres of dense nebulae, which arise within these interstellar clouds. Violent winds and the ultra-violet radiation of young massive stars erode and perturb the molecular cloud from which they were born.
The superb pictures obtained with optical telescopes show the interaction of light and matter on the surface of these clouds.
However, the regions where stars could be born later, the so-called dense cores, emit only radio millimetre radiation. They cannot be seen with optical telescopes.
That is why astronomers use world class telescopes such as the IRAM 30m telescope.
The international ORION- B project has obtained, using the 30m radio-telescope, the most complete to date structure in the radio domain of the Orion B nebula.
A voyage in the entrails of the cloud
Jérôme Petyexplains: "/We have been observing the well known Horse’s Head nebula for over a decade. However, only the recently installed 30m instrument at the IRAM has enabled us to obtain images 100 times larger than ever before, and simultaneously at many wavelengths !/"
The 30m telescope detects the signals coming emitted by diverse molecules in space (carbon monoxide, carbon sulfide, cyanide, methane, small hydrocarbon molecules, etc...).
images which have been obtained show that different molecules are distributed in very different ways: depending on their chemical evolution, the molecules are found in extraordinarily different regions of the cloud. This is precisely the feature which enables astronomers to characterize the various stages of stellar formation.
For example, the diffuse and turbulent phases occupy much of the volume, while on the contrary the dense cores only occupy a few percent. Between theses phases, matter is grouped along filaments.
The closest ever view of stellar formation
The ORION- ‐B data throw light on one of the key questions of contemporary astrophysics, which is to understand why molecular clouds give birth to so few stars?
In effect, while the clouds should collapse under their own weight to form dense cores, only a few percent of the clouds do actually transform into stars.
And so what are the parameters which govern star formation?
A possible reason is related to the nature of gas motions: for a give constant n turbulence, compressive motions lead to the collapse of the dense cores, forming stars, while rotations constitute an efficient barrier to gravitational collapse. That is what we have shown, for the first time/" explains Maryvonne Gerin, CNRS research director at the Laboratoire d’Étude du Rayonnement et de la Matière en Astrophysique et Atmosphères (LERMA) of the Paris Observatory.
Big data meets millimetre radio-astronomy
The ORION- ‐B project produce, per secocnd, s on the order of 160 000 images, or 1h50 of film at the rate of 24 images per second!
There is no doubt that this kind of radio observation will become current in the near future. Thus, the pioneering statistical studies of the ORION- ‐B project will have delivered the essential tools and experience to engage in more ambitious analyses.
