Situated in the constellation of Orion, at a distance of 1300 light years from the Earth, the Horsehead Nebula is not just one of the most famous nebulae in the sky. Its outline, bathed in light, is above all an incredible interstellar laboratory, where dense gases and stellar radiation come into contact.
With the help of the IRAM 30m radiotelescope, situated in the neighbourhood of Grenada, in Spain, Jérôme Pety, IRAM astronomer at the Observatoire de Paris and his team completed a systematic survey of chemical molecules in the mane of the Horsehead Nebula during a project called Horsehead WHISPER. « The refurbishment of the instruments of the IRAM telescope enabled us to observe in one week what would previously have taken a whole year. This opens the door to new possibilities for the classification of gas clouds in the Universe, as a function of the molecules they contain. » said Pierre Gratier, a member of the team.
This work led to the detection of about thirty molecules, confirming the chemical complexity of the processes at work in the famous nebula. Among these molecules are numerous small hydrocarbons, the smallest of the molecules which make up petrol and natural gas. « The nebula has 200 times more hydrocarbons than there is water on the Earth ! » enthused Viviana Guzman, a Chilean student at the IRAM. One of these small hydrocarbons, the cation propynylidynique (C3H+), had until now never been found in space. This cation is a key actor in the chemical reactions which bind the small hydrocarbons to each other.
Where do all these hydrocarbons come from ? In their paper, Jérôme Pety and his colleagues explain their presence by the fragmentation of the carbon based molecules called PAH. Under the influence of interstellar radiation, these could have been broken up, into a large number of small hydrocarbons. This process would be particularly efficient in the region of the Horsehead, where the interstellar gas is exposed directly to the radiation of a very close massive star. « We are looking directly at a natural petrol refinery on a huge scale. », concluded Jérôme Pety.
Notes
The Institut de Radioastronomie Millimétrique IRAM (the institute for millimeter radioastronomy) was founded by the Centre National de la Recherche Scientifique (National Center for Scientific Research) in France and the Max-Planck-Gesellschaft in Germany, later joined by the Instituto Geográfico Nacional in Spain. Its head office is in Grenoble, it has a 30m diameter radiotelescope at the Pico Veleta in Spain, and a 6 telescope interferometer with 15m diameter telescopes on the Plateau de Bure in the French Hautes-Alpes.
The scientific team
J. Pety (IRAM, LERMA [1]./Observatoire de Paris, CNRS, Université de Cergy-Pontoise, Université Pierre et Marie Curie, ENS), P. Gratier, V.Guzman, S.Bardeau (IRAM, Grenoble, France), A.Sievers (IRAM, Granada, Spain), M. Gerin (LERMA/Observatoire de Paris, CNRS, Université de Cergy-Pontoise, Université Pierre et Marie Curie, ENS), E. Roueff (LUTH [2]/Observatoire de Paris, CNRS, Université Paris Diderot), F. Le Petit (LUTH/Observatoire de Paris, CNRS, Université Paris Diderot), J. Le Bourlot (LUTH/Observatoire de Paris, CNRS, Université Paris Diderot), J. Goicoechea (CSIC/INTA, Madrid, Spain), A. Belloche (MPIfR, Bonn, Germany), D. Talbi (LUPM, Montpellier, France).
[1] The Laboratoire d’Etude du Rayonnement et de la Matière en Astrophysique LERMA is a department of the Observatoire de Paris. It is associated with the CNRS, with the Cergy-Pontoise University, with the Pierre and Marie Curie University, and with the Ecole Normale Supérieure
[2] The Laboratoire Univers et Théories LUTH is a department of the Observatoire de Paris. It is associated with the CNRS et and with the Paris Diderot University.