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Surprises in the Rotten Egg Nebula

We had already spoken before about the presence of smelly gases in astrophysical environments. Now, a team of researchers has discovered new molecular species with nitrogen in a circumstellar envelope known as a Pumpkin Nebula or Rotten Egg Nebula. Why that name? Cover your nose…

Image 1: Messier 46 (Pumpkin Nebula or Rotten Egg Nebula).

Dying stars are real molecule factories, as they throw into the interstellar medium part of the material that forms them, creating a kind of cloud of gas and dust around them called “circumstellar envelope”. Using the IRAM 30m radio telescope, a team of researchers has discovered new species with nitrogen (N) in OH231.8+4.2, an oxygen-rich circumstellar envelope also known as the Pumpkin Nebula or Rotten Egg Nebula.

For about 40 years, circumstellar chemistry has been a fertile source for new molecular discoveries and for the development of physical and chemical models. Circumstellar envelopes around evolved stars (at the stage of the Asymptotic Giant Branch or AGBs) are formed as a result of the intense mass loss process suffered by these objects and are composed mainly of molecular gas and dust, which makes them the areas of space with one of the most complex chemical environments.

These circumstellar envelopes are classified according to the relative abundances of carbon and oxygen, being rich in one element or another, which will determine what kind of chemistry will predominate in each of these environments.

In the case of oxygen-rich circumstellar envelopes, carbon plays the role of “limiting reagent” and is almost entirely contained in carbon monoxide (CO), which is a very abundant and stable species, while the remaining oxygen is free to react with other atoms, forming additional oxygen-carrying molecules.

For this reason, apart from CO, oxygen-rich circumstellar envelopes are relatively poor in carbon-carrying molecular species, while carbon-rich envelopes show low abundances of oxygen-carrying species. To date, most observation efforts to detect new circumstellar molecules had focused on carbon-rich sources, as they are believed to have a more complex chemistry than their oxygen-rich counterparts (in fact, the most studied object of this type is the evolved star CW Leonis, in whose envelope some 80 molecules have been discovered).

However, recent work suggests that oxygen-rich envelopes may be chemically more diverse than originally thought. For example, some unexpected chemical compounds (such as HNC, HCO+, CS, CN, etc.) have been identified in a number of oxygen-rich late-type stars, including the Rotten Egg Nebula, studied in this work: using data obtained with the IRAM 30m telescope, in a survey conducted at millimeter wavelengths, the molecular species HNCO, HNCS, HC3N and NO have been detected [1].

This work encloses many “first times”: this is the first time HNCO and HNCS have been detected in any type of circumstellar envelope; it is the first time HC3N has been detected in an oxygen-rich envelope; finally, the finding of NO (nitrogen monoxide) represents the first detection in an envelope around an evolved low/intermediate mass star (stars with a mass between one and eight times the mass of the Sun).

The importance of these detections lies not only in their discovery, but also in that they also give us clues to the chemical processes that could form them: the study of this finding suggests that shock processes could be the cause of their formation. But first, let’s get to know our protagonist a little more.

Image 2: Area of the sky where Messier 46 (the Pumpkin Nebula or Rotten Egg Nebula) is located.

OH231.8+4.2, the Pumpkin or Rotten Egg Nebula

OH231.8+4.2 [2] is a well-known bipolar nebula that is also known as the Rotten Egg Nebula (by the way, it could also be called the pestilent nebula… as you know, it’s not the first time we’ve talked about stinky gases or other compounds with a characteristic bad smell. In this case, our nebula has so many sulphurous compounds that the thing must be very bad up there).

The evolutionary stage of this nebula is unclear due to its multiple and unusual properties. It is believed to be a precursor to planetary nebula detected, probably in a short-lived transition phase. The central star is QX Pup [3], and is obscured in the visible range by gas and dust.

The late evolution of this object may have been complex, as it has a binary companion star indirectly identified from the spectral analysis of light reflected by the nebula.

A companion star could influence and alter a circumstellar envelope in both physical (for example, due to the influence of its gravitational field) and chemical development (for example, if it is very hot, it could emit ultraviolet-like light capable of dissociating some of the molecules).

Most nebular material is found in the form of cold and massive molecular gas and dust. This gas is found in a very elongated and lumpy structure formed by two main components: a central core and a highly collimated bipolar jet.

Both the presence of bipolar jets and the presence of shocks are common characteristics to objects that have left the AGB phase and are evolving into the planetary pre-nebula phase.

However, this nebula still preserves characteristics related to the spherical star envelope that are still in the AGB phase. In fact, the central star, QX Pup, is classified as AGB. As we said at the beginning, it is not clear to us at what stage of her life the star is at, and it is likely to be in a moment of transition: we have caught this star “in fraganti”.

But that is not the only topic of debate: it is still discussed what the process that gave rise and shape to this nebula as we see it today has been. It is believed that, at first, a spherical envelope was created around the AGB star (which occurs in most stars of this type). However, a mechanism of unknown origin created bipolar jets of collimated and strongly accelerated matter [4]. The shock of these jets with the AGB envelope, which previously occupied that place in the pole area, would push that material away from the star, creating that form of pumpkin or hourglass.

The origin of these differences and the acceleration itself [5] is likely to be a consequence of the presence of this potential star companion, a plausible scenario that has been proposed to explain the shape and acceleration of bipolar planetary pre-nebulae and planetary nebulae.

The importance of shocks

We let you in standby, yearning for more, by overtaking you of the importance of shocks in this research work. After studying and comparing the observations and results of the models, it was inferred that the amounts found of these molecular species in this nebula (remember, HNCO, HNCS, HC3N and NO) could not be a product of UV photon-induced chemistry or cosmic ray-induced chemistry, and that other processes, such as shocks, played an important role in their formation.

It is very likely that the molecules located in the shock zone, which is located between the jet and the spherical envelope, dissociate. Material may even have been extracted from the dust grains. Then, after the shock, the collided material would cool over time, thus allowing new molecules to form again.

In short, this survey in the millimeter range has led the team to obtain very detailed information about the overall physical-chemical structure of this envelope. OH231.8+4.2 could be the best example of an environment around an evolved star that has suffered shocks and therefore a unique environment for the study of chemical processes induced by these shocks.

Rotten eggs, violent impacts, smelly gases… our oxygenated nebula seemed like a dull environment. But it is full of action.

More information:

Paper: “New N-bearing species towards OH231.8+4.2: HNCO, HNCS, HC3N and NO”. Authors: L. Velilla Prieto (Molecular Astrophysics Group, ICMM-CSIC; Astrobiology Center, CAB/INTA-CSIC, Spain); C. Sánchez Contreras (CAB/INTA-CSIC, Spain); J. Cernicharo (Molecular Astrophysics Group, ICMM-CSIC; CAB/INTA-CSIC, Spain); M. Agúndez (Molecular Astrophysics Group, ICMM-CSIC; CAB/INTA-CSIC, Spain; Laboratoire d’Astrophysique de Bordeaux, LAB/Université de Bordeaux, France); G. Quintana-Lacaci (Molecular Astrophysics Group, ICMM-CSIC; CAB/INTA-CSIC, Spain); J. Alcolea (National Astronomical Observatory, OAN-IGN, Spain); V. Bujarrabal (OAN-IGN, Spain); F. Herpin (LAB/Université de Bordeaux, France); K. M. Menten (Max-Planck Institute for Radio Astronomy, Germany); and F. Wyrowski (Max-Planck Institute for Radio Astronomy, Germany).

Notes

[1] In addition to these molecular species, this survey in the millimeter range has detected hundreds of molecular transitions, discovering more than 30 new species (including different isotopologues) and expanding the sequence of rotational transitions detected for many other species at this source.

[2] Discovered by Turner (1971), the OH231.8+4.2 bipolar nebula surrounds an OH/IR source: OH/IR objects -seen in the infrared- are evolved bright stellar objects with an envelope featuring an eminent OH maser emission.

[3] This star is classified as M9-10 III and has a Mira-type variability consistent with an evolved AGB star. 

[4] With speeds of up to ∼400 km s−1.

[5] It appears that the acceleration of the lobes could have taken place about ∼800 years ago in less than ∼150 years and it is believed that the low-speed central core is probably the fossil vestige of the AGB’s circumstellar envelope.

Images:

Image 1: Messier 46 (Pumpkin Nebula or Rotten Egg Nebula). Credits: Valentín Bujarrabal (OAN, National Astronomical Observatory, IGN, Spain), WFPC2, HST, ESA, NASA.

Image 2: Area of the sky where Messier 46 (the Pumpkin Nebula or Rotten Egg Nebula) is located. Credits: ESA; Valentín Bujarrabal (National Astronomical Observatory, IGN, Spain) and Digitized Sky Survey.

Originally published in Spanish on the Naukas website:  Sorpresas en la nebulosa del Huevo podrido (2015/04/07).

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Hydrocarbon open bar in Orion

1. The Trapezium in the Orion Nebula

Using the IRAM-30m radio telescope and sophisticated interstellar chemistry models, an ASTROMOL team has studied the composition and spatial distribution of small hydrocarbons in the “Orion Bar”, a clear example of molecular cloud radiated by ultraviolet light

Hydrocarbons are the simplest organic molecules, formed only by hydrogen and carbon. They are one of the main sources of energy in the modern world, as they are part of oil, natural gas, gasoline; they are also found in many materials that we usually use, such as plastics, fibers or paints, and we even walk on them every day as they are the main component of asphalt.

But not only can we find hydrocarbons on our planet: since the 1970s it is known that hydrocarbons are present in much of the interstellar environment, and one of the issues that astrochemistry has been looking to clear since then is how they form and what their chemical behavior is in that environment.

In order to study them, one of the most appropriate environments are Photodissociation Regions (PDRs), transition zones between cold and neutral gas (mostly molecules) protected from ultraviolet radiation, and atomic and ionized gas, illuminated by intense ultraviolet fields mostly coming from massive stars [1].

Photodissociation regions are found in many astrophysical environments and on many spatial scales, from the nuclei of star-forming galaxies to the illuminated surfaces of protoplanetary disks. All of them show a chemistry whose common characteristic is the photodissociation of molecules caused by ultraviolet radiation.

The most spectacular and close example of this type of photodissociation region is the so-called Orion Bar, which is located within the well-known Orion Nebula, located about 1,300 light-years from Earth. The Orion Nebula is one of the most studied astronomical objects of all time: it is an immense cloud of gas and dust lovingly regarded as a stellar nursery, as thousands of stars begin their lives there. It is not the only stellar nursery in the galaxy but, being the closest forming massive stars (more than 8 times the mass of the Sun), it offers us the opportunity to study in detail how the stars are born; how, once formed, they interact with the interstellar environment that surrounds them; and, in particular, how intense stellar ultraviolet radiation fields end up “destroying” (photodissociating) the molecular cloud where they were born.

Ultraviolet radiation that ionizes atoms and dissociates molecules in the Orion Bar comes from the famous set of massive stars in the Trapezium cluster, which takes its name from the asterism that make up its four brightest stars.

Having a chemistry controlled by ultraviolet radiation makes that, in these regions, very peculiar species are produced, such as radicals (C2H, OH, HCO…) and ions (SO+, CO+, CH+, HOC+, etc.). These species do not exist naturally on our planet, as they are extremely reactive and unstable and quickly react with other molecules to form new, more stable compounds. They can only be formed in the laboratory under very specific controlled conditions.

2. Center of the Orion Nebula

The study of the Orion Bar

In order to establish the limits of the chemical complexity of the interstellar environment, and using data obtained with a spectral mapping [2] carried out with the IRAM-30m radio telescope (located in Sierra Nevada, Granada, Spain), an ASTROMOL team has managed to expand our knowledge of which molecules exist in environments radiated by strong fields of ultraviolet radiation and how they form.

Although the Orion Bar is a hostile environment where you would expect only very simple molecules, observations show a spectrum with more than 500 lines coming from the emission of more than 60 different molecules containing 2 to 6 atoms. What is surprising is that approximately 40% of the detected lines belong to hydrocarbons [3]! So, it’s all about making a word game and claiming that we have an area with a hydrocarbon open bar in Orion.

But how do these hydrocarbons form in the interstellar environment and why are they so abundant? Until now, in studies in other regions radiated by less intense ultraviolet radiation fields, such as the famous Horsehead Nebula, or in interstellar diffuse clouds, the results obtained through the analysis of observations did not match the theoretical results obtained from gas phase models [4]. The abundances of hydrocarbon measured in these regions were much greater than those predicted by these models. That is, gas chemistry was not enough to explain these high abundances.

Researchers looked for alternative sources of carbon that might be contributing to the amount of hydrocarbons formed through gas reactions, and thought about polycyclic aromatic hydrocarbons (PAHs). PAHs are powerful environmental pollutants, but they are also present ubiquitously in the universe (see image 2). In these regions, the incidence of radiation on PAHs would completely break down the cyclical structure of these compounds, forming small hydrogen and carbon molecules, and contributing to the amount of hydrocarbons formed by gas phase reactions.

However, the ASTROMOL team has discovered that, to explain the high abundances of hydrocarbons in the Orion Bar, there is no need to resort to the destruction of PAHs (or their contribution is not the dominant one) as Trapezium stars illuminate the region with ultraviolet radiation fields so intense that molecular gas reaches very high temperatures, bringing into action new gas chemical reactions that need very high energies to occur [5].

This takes a step further in understanding the results and details of photodissociation in gas clouds, helping us improve our knowledge of interstellar carbon chemistry and learn more about how chemical complexity in space increases.

3. Hydrocarbon Spectra in the Orion Bar

Notes

[1] Generally, massive OB-type stars, at least 8 times more massive than the Sun and main source of ultraviolet radiation in galaxies like ours.

[2] Spectral maps are one of the most important tools in the field of astrochemistry to study the interstellar medium, as they allow to carry out a complete chemical characterization of the region under study. In this case, spectral lines have been obtained in the millimeter range, one of the lowest energy in the electromagnetic spectrum and whose emission is dominated by low-energy transitions produced by molecules.

[3] C2H, C4H, c-C3H2, c-C3H, C13CH, 13CCH, l-C3H, l-C3H+ and l-H2C in decreasing order of abundance.

[4] These models attempt to computationally simulate the physical and chemical conditions of interstellar clouds, simulating hundreds of chemical reactions and processes that occur in different regions.

[5] Endothermal reactions (or with barriers, i.e. those that only occur from certain temperatures) in gas phase between C+, radicals and H2, can dominate chemistry and promote the formation of hydrocarbons. However, photodissociation of PAHs, hydrogenated amorphous carbons (HACs) and very small grains (VSGs) may be required, as well as a greater knowledge of surface chemistry in carbonous grains to explain the abundances of the most complex hydrocarbons.

More information

This work has been published in the scientific paper “The chemistry and spatial distribution of small hydrocarbons in UV-irradiated molecular clouds: the Orion Bar PDR”, and the authors are S. Cuadrado (Molecular Astrophysics Group of the Institute of Materials Science of Madrid (ICMM, CSIC); Astrobiology Center (CAB/CSIC-INTA), Spain; J. R. Goicoechea (Molecular Astrophysics Group of the ICMM-CSIC; CAB/CSIC-INTA, Spain); P. Pilleri (Université Toulouse III – Paul Sabatier, UPS- Observatoire Midi-Pyrénées, OMP – Institut de Recherche en Astrophysique et Planétologie, IRAP); Centre national de la recherche scientifique, CNRS – IRAP, France);  J. Cernicharo (Molecular Astrophysics Group of the ICMM-CSIC; CAB/CSIC-INTA, Spain); A. Fuente (National Astronomical Observatory, OAN-IGN, Spain); and C. Joblin (Université de Toulouse UPS-OMP, IRAP; CNRS, IRAP, France). 

Links

Images:

1. The Trapezium in the Orion Nebula.

At the center of this image, surrounded by dust and gas, we see the intense brightness of the stars that make up the Trapezium, the four most massive stars of the Orion Nebula. The ultraviolet radiation they emit alters the chemistry of their entire environment. http://hubblesite.org/newscenter/archive/releases/2006/01/image/e/

Credits: NASA,ESA, M. Robberto (Space Telescope Science Institute/ESA) and the Hubble Space Telescope Orion Treasury Project Team.

2. Center of the Orion Nebula

Image of the center of Orion Nebula in the infrared (at 8 microns) taken by the IRAC camera aboard the Spitzer Space Telescope (data from NASA/Spitzer’s public file: http://archive.spitzer.caltech.edu). At these wavelengths the emission is dominated by polycyclic aromatic hydrocarbons (PAHs). It also shows the position of the Trapezium Cluster (marked with stars) and the region studied in this work (the green box). Credits: NASA/Spitzer; Javier R. Goicoechea

3. Hydrocarbon Spectra in the Orion Bar

Spectra of the Orion Bar at 85 GHz. Three lines (rotational transitions) of two different hydrocarbons (C4H and C3H2) and a hydrogen recombination line from the atomic and ionized gas region (HII region) can be observed.

Originally published in Spanish on the Naukas website: Barra libre de hidrocarburos en Orión (2015/03/11).

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Something smells rotten… in Orion KL

Literally. The Kleinmann-Low massive star-forming region is part of Orion’s molecular cloud, and is therefore known as Orion KL. In its surroundings, the possible presence of ethyl mercaptan, a gas characterized by its smell of rotten eggs, has been detected. Hence the phrase, uttered by Marcellus’ character in the first act of Shakespeare’s Hamlet, fits to perfection in this story.

Orion KL.

Mercaptan (better known as thiol) is a compound formed by a sulfur atom and a hydrogen atom (-SH). In the case of methyl mercaptan (CH3SH), we are talking about a colorless gas that gives off a strong odor.

But for those who investigate its presence in space, smell is not a problem. Any possible presence of molecular gas is capable of study, whatever its characteristics are (smell of flowers or sewer). In fact, methanol (CH3OH) and ethanol (CH3CH2OH), two molecules chemically similar to those already mentioned in which only one atom (OàS) changes -and which we are also going to talk about- are well known in many astrophysical environments.

The methyl mercaptan itself was detected in 1979 by Linke and collaborators at SgrB2, a molecular cloud of the galactic center known to be one of the most productive massive star formation areas in the galaxy. Subsequent studies also detected the presence of methyl mercaptan in two very different locations: in the cold molecular cloud B1 (this cloud is located in the so-called First Hydrostatic Core stadium, which is formed when the collapse phase at the star’s birth stage stops); and towards the hot core of G327.3-0.6, a massive star-forming region.

For the research team I’m going to talk about, the detection of methyl mercaptan is actually a key to try to determine whether another compound, ethyl mercaptan (CH3CH2SH), the thiol equivalent for ethanol, is present in those same areas.

Ethyl mercaptan does not leave its methyl relative behind in terms of danger: extremely irritating, corrosive and sensitizing in case of skin contact and very dangerous in case of eye contact, inhalation or ingestion. Nor is its smell very pleasant. In fact, it is one of the components added to butane and propane gas: these gases have no odor, so, to detect leaks, this odorant compound is added to them. Hence, when there’s a gas leak, it smells like rotten eggs.

The finding

In a work led by Lucie Kolesniková, involving other members of Consolider ASTROMOL (Belén Tercero and José Cernicharo, among others) has detected the possible presence of ethyl mercaptan towards Orión KL.

A survey of this area, the most active part of the Orion Nebula, carried out in the range of millimeter waves with the IRAM 30m radio telescope [1], resulted in the detection of more than 8,000 spectral lines unknown so far. Each spectral line is identified by a particular transition of a molecular species (the footprint left by the molecule when it passes from one energy state to another). Many of them (nearly 4,000) have already been identified as isotopologue-derived lines [2] and excited vibrational states [3] of abundant and well-known species in the interstellar environment, significantly reducing the number of unknown lines and mitigating the confusion of lines in the spectra.

Several of these lines could correspond to ethyl mercaptan transitions, but to confirm this, experiments had to be conducted in molecular spectroscopy laboratories where the frequencies of the ethyl mercaptan rotation spectrum could be measured and predicted with sufficient spectroscopic accuracy. These experiments resulted in the possible presence in Orion of the gauche and trans conformers of ethyl mercaptan.

What is a conformer?  Atoms, when joined, can do so in different ways. Their simple links allow them to rotate the groups, as they have cylindrical symmetry. Because they can rotate around their link, they adopt different spatial arrangements: this is called conformation, and a specific conformation is a conformer. The gauche conformer (left, in French) has the hydrogen of the SH group at 120o and 240o with respect to the link –SH, and the trans at 0o.

Para esta especie, el gauche es el confórmero más estable de los dos y, aunque no se puede asegurar al cien por cien la presencia del confórmero trans (aún debe confirmarse con posteriores comprobaciones observacionales), es la primera vez que se detecta mercaptano de etilo en el medio interestelar. Aún así, la detección está en el límite de nuestras posibilidades de detección y el equipo recomienda ser cautos hasta que lleguen nuevas observaciones que permitan corroborarla.

For this species, the gauche is the most stable conformer of the two and, although the presence of the trans conformer cannot be guaranteed 100 percent (it has yet to be confirmed with subsequent observational checks), it is the first time that ethyl mercaptan is detected in the interstellar medium. Even so, detection is at the limit of our detection possibilities and the team recommends being cautious until new observations arrive to corroborate it.

The dust grains

Comparing the proportion of ethyl mercaptan to methyl mercaptan, the results confirm that the second would be ≃5 times more abundant than the first in the hot core of Orion KL. That difference was actually expected to be much greater, but why might it not be?

This study found that, in Orion KL, methanol (CH3OH) is 30 times more abundant than ethanol (CH3CH2OH), from which it could be inferred that, as methyl mercaptan (CH3SH) and ethyl mercaptan (CH3CH2SH) are chemically similar to the previous ones, the difference should also be similar. However, as we have already pointed out, the relationship between CH3SH/CH3CH2SH was only 5, creating a somewhat surprising value.

Researchers believe the difference could be due to methanol and methyl mercaptan remaining for different times on the dust grains before evaporation. If methyl mercaptan sticks to dust grains longer than methanol, more chemical processes could take place, changing the abundances between methyl (CH3-) and ethyl (CH3CH2-) species.

Considering that the emission of the species −OH in Orion KL comes mainly from a compact area at about 150 K of kinetic temperature (called compact ridge) while the ethyl and methyl mercaptan emit from the hot core at a temperature of more than 200 K, the relative abundance differences between the methyl and ethyl species could also be due to chemical differentiation between these two regions within Orion KL.

More sensitive observations are needed to derive the possible amounts of the two ethyl mercaptan conformers and study their spatial distribution in Orion. This will be possible with interferometers such as ALMA, the crème de la crème of the cold universe and a tool that will undoubtedly bring great answers to the field of Astrochemistry.

The universe never ceases to amaze us by its richness. Recently, the discovery of methyl acetate and the gauche conformer of ethyl formate, among others (another result obtained by members of Consolider ASTROMOL) were released. Many of the lines observed in space remain unidentified, and the more sensitive our instruments are, the more abundant and defined those lines are. Confirmation of new molecular species, based on precise laboratory measurements, remains a field of research of great activity. And while important steps have been taken, there is still work ahead to confirm whether something actually smells rotten in Orion KL.

Notes

[1] The IRAM 30m telescope is a millimeter telescope equipped with a series of receivers that allow it to make high-resolution spectroscopy, thus studying the role that chemistry plays in the formation of stars, both within giant molecular clouds of the Milky Way and in nearby galaxies, or off, on farthest known galaxies of the young universe. The telescope is located on Pico Veleta, in Sierra Nevada (Granada, Spain), at an altitude of 2,850 m. More than 50 molecules have been detected with this telescope, most of them by scientists from this Spanish team (Consolider ASTROMOL).

[2] When we have two atoms of the same element with the same number of protons, but with a different amount of neutrons in their nucleus, we have two isotopes. When, on the other hand, we have a molecule that has at least one isotope, then we will have an isotopologue of that molecular species.

[3] Molecules have different energy levels: electronic, vibrational and rotational. Because the energy is quantized, we can know what kind of transition has taken place when a molecular species is excited or deexcited. Within a particular electronic state, the molecule can reach different types of vibrational states (those produced by the vibration of the atoms that make up the molecule) and, in turn, within the same vibrational state, the molecules rotate, producing a rotation spectrum that can be detected with radio telescopes in the domain of millimeter and submillimeter waves.

More information:

These results were published in the scientific paper “Spectroscopic characterization and detection of Ethyl Mercaptan in Orion“, in the Astrophysical Journal, 784, L7.

The authors are L. Kolesniková (Molecular Spectroscopy Group (GEM), Spectroscopy and Biospectroscopy Laboratories, Unidad Asociada CSIC, University of Valladolid, Spain); Belén Tercero (Astrophysics Department, Astrobiology Center CAB, CSIC-INTA, Spain); José Cernicharo (Astrophysics Department, Astrobiology Center CAB, CSIC-INTA, Spain); J. L. Alonso (Molecular Spectroscopy Group (GEM), Spectroscopy and Biospectroscopy Laboratories, Unidad Asociada CSIC, University of Valladolid, Spain); A. M. Daly (Molecular Spectroscopy Group (GEM), Spectroscopy and Biospectroscopy Laboratories, Unidad Asociada CSIC, University of Valladolid, Spain); B. P. Gordon (Division of Natural Sciences, New College of Florida, Sarasota, Florida, USA); and S. T. Shipman (Division of Natural Sciences, New College of Florida, Sarasota, Florida, USA).

Images:

In the box we can see the protagonist area of our story: Orion KL. Credits: (NASA, ESA, Robberto (STScI/ESA), Orion Treasury Project Team).

Links:

About ethyl mercaptan in the list of molecules discovered in space, maintained by the Institute of Physics of the University of Cologne.

Originally published in Spanish on the Naukas website: Algo huele a podrido… en Orión KL (2014/07/17).