The Universe is full of objects, each more amazing than the next. Among the stars, planets, black holes or even nebulae, it is also possible to come across giant molecular clouds of alcohol.
At 6500 light years from Earth, there is a somewhat special region since it contains a giant molecular cloud of alcohol approximately 500 billion kilometers long. Located in an area named "W3(OH) », this cloud is mainly composed of methanol (methyl alcohol) and ethanol (ethyl alcohol) for a small fraction (the drinkable form). Although such a cloud may seem strange, many chemical reactions take place within molecular clouds and the formation of complex chemical molecules and compounds is not uncommon. Especially since alcohol is a relatively simple molecule, composed of hydrogen, oxygen and carbon.
This structure was observed by a team of British astrophysicists from the Jodrell Bank Observatory in 2014, thanks to the MERLIN radio telescope. The existence of an alcohol cloud is not only a matter of curiosity, it also offers extremely interesting properties for astrophysics. The abundance of simple and identical molecules gathered in the same place, can lead to a stimulated light emission if the necessary energy is brought to the system. Under these conditions, the phenomenon is known as "astrophysical maser ". The acronym maser stands for microwave amplification by stimulated emission of radiation; when this process uses the visible part of the electromagnetic spectrum, it is a laser.
stimulated emission differs from spontaneous emission in which a molecule or an atom randomly emits a photon. The electron of an atom is in an excited state (higher energy level) and upon de-excitation (going from an "n" energy level to an "n-1" level) it emits a photon. The quantum model of the atom imposes on the electron well-defined (discreted) energy levels, therefore the photon emitted during spontaneous emission also has a determined energy.
But when the electron in an excited state is struck by a photon, this can trigger the de-excitation of the electron and the emission of a photon:this is stimulated emission. However, not just any photon can cause this de-excitation; the photon must have a wavelength corresponding exactly to the transition energy between the two electronic states. In the case of a molecular structure, the photon emitted from an electron by stimulated emission can strike another electron and cause a cascade of stimulated emission. The flow of photons thus causes a strong light emission on a particular wavelength.
Three conditions are necessary to obtain an astrophysical maser:one or more molecules with an intense emission spectrum, a local concentration of these molecules and finally a source of energy sufficient to trigger spontaneous emission. W3(OH) has all these characteristics. Indeed, methanol molecules have a characteristic emission spectrum, they are densely grouped together within a cloud, and this cloud surrounds a stellar nebula whose proto-stars constitute an important source of energy.
The observations revealed gigantic filaments of gas linked together and constituting the various maser sources. These data changed the formation models of astrophysical masers, which suggested that they could only exist as isolated points and not as linked structures. In addition, observations showed that the cloud revolved around a central stellar area with a high rate of star formation.
The maser was invented in 1953 by American physicists Charles Townes, James P. Gordon and Herbert Zeiger of Columbia University. It was then an optical ammonia maser. For a long time, scientists thought that the maser could only be of artificial origin, strictly human creations. Thanks to discoveries like W3(OH), physicists now know that astrophysical masers also populate the Universe.
Source:Royal Astronomical Society
