Old and new

Bet on what we already have

40m Yebes Telescope at the Astronomical Center of Yebes (Spain)

Those who know me know that I am a strong advocate of betting on the development of technology in telescopes. Not for nothing did I work for a while for the Gran Telescopio Canarias and I saw how its level of competitiveness was endangered by not investing enough at the time: they would have left us with a great telescope, but without frontier instruments to get the best out of it.

Over time I have ended up working on a branch of astronomy that observes what happens in the coldest ranges of the light spectrum. In these ranges radioantennas are used, and in Spain we have a few installed.

In recent decades other countries have built and improved similar facilities. And it’s ugly to say it, but few bet on this antenna that I’m going to talk about when there were others that were yielding very good results in terms of accuracy and sensitivity.

A few weeks ago I attended online a talk by José Cernicharo (researcher at the Institute of Fundamental Physics of the CSIC), recently awarded the Miguel Catalán Prize 2020 for the scientific career, awarded by the Community of Madrid. The talk, designed to make known to people of the guild the latest results obtained, was a mixture of passion and joys. Cernicharo has been working all his life in the study of space chemistry and molecular astrophysics. In recent years he coordinates the European project NANOCOSMOS together with two other principal investigators, Christine Joblin (CNRS, France) and José Ángel Martín Gago (ICMM-CSIC, Spain). Nanocosm is a challenge in all its facets, since it pushes the frontier of knowledge with a risky and complex proposal. Not surprisingly, the Synergy Grants granted by the ERC (European Research Council) are bets that seek this difficulty, even at the risk of not obtaining the results originally intended. That is how science is and that is how it must be defended.

Machines to know the smallest universe

The case of Nanocosmos is a step towards discovery that unites science and technology, with several machines developed within the project that are giving surprising results.

The Stardust machine is a machine built from scratch, using, of course, the knowledge of those who have a lot of experience in surface science, but with objectives specifically aimed at clearing up unknowns related to astrochemistry, with knowing how dust grains are formed in the envelopes of evolved stars.

Developed at the Institute of Materials Science of Madrid (ICMM-CSIC) by José Ángel Martín Gago and his team, this machine is capable of synthesizing dust grains “a la carte” and make them go through several phases to determine their behavior under specific physical conditions. This helps us to confirm what is observed with antennas and telescopes.

The GACELA (Gas Cell for Chemical Evolution) simulation camera has been that link that unites the new and the old. Installed in Yebes, it uses the same receivers that have been installed in the 40m Yebes radio antenna. This camera studies the interaction of small particles with the earth’s primitive atmosphere and has a very high precision to define the composition of the gas.

Finally, the AROMA machine serves to take this later step in the analysis: the samples obtained in the Stardust machine and in GACELA are analyzed.

These three machines are the protagonists of this short, ten-minute video, which talks about how they work and what their first results have been. They help us to complete the puzzle of information offered by simulations, observations and, finally, the experiments themselves. In fact, there’s a phrase I can’t forget from an interview I did some time ago with Louis Le Sergeant d’Hendecourt (of the Astrochemistry and Origins team at the Institute of Space Astrophysics (CNRS-UPS) in France): “Laboratory astrophysics is the supreme judge in astrochemistry.”

New receivers, increased sensitivity

The Astronomical Center of Yebes (Centro Astronómico de Yebes, National Geographic Institute, Spain) has several tools, and one of them, the largest, is the 40m radio antenna of Yebes. Since 2010, it has focused on Very Long Baseline Interferometry (VLBI), acting in conjunction with other radio antennas located at different points on the planet, as well as single antenna observations, acting alone. It has been covering specific frequency bands (mainly between 2 GHz and 90 GHz in discontinuous and narrow windows) in order to meet the current needs of the European VLBI Network (EVN) and the The Global mm-VLBI Array (GMVA).

But the Nanocosmos project decided to bet on improving its performance, providing specific receivers aimed at meeting the objectives of the project. To be honest, we’re so used to betting on new things and discarding the “old” that sometimes we’re not aware of how valuable some tools are. In fact, Japanese researchers did something similar with the Nobeyama’s 45m Telescope, but the level of sensitivity obtained by the 40m Yebes Telescope is much higher.

The combination of the old and the new has been overwhelming: the teamwork developed by all the staff of the Astronomical Center of Yebes, together with the commitment of Nanocosmos, has managed to increase the instantaneous coverage of frequencies to observe numerous molecular transitions simultaneously. This reduces observation time and maximizes data output from the telescope (this paper describes the technical specifications of these receivers). It highlights the improvement in sensitivity in the Q band (but also in the W), with observational results that open the possibility of studying the spectrum of different astrophysical environments with an unprecedented sensitivity.

La primera muestra de ello es un barrido espectral que puede considerarse como una hazaña. Ya durante la fase de pruebas de los receptores se realizaron observaciones de muy alta sensibilidad, revelando el enorme potencial del nuevo equipamiento del radiotelescopio: en muy poco tiempo se han descubierto 11 nuevas moléculas (y lo que queda por descubrir).

The first example of this is a spectral sweep that can be considered a feat. Already during the testing phase of the receivers, observations of very high sensitivity were made, revealing the enormous potential of the new equipment of the radio telescope: in a very short time 11 new molecules have been discovered (and what remains to be discovered).

The TMC-1 sweep and IRC+10216 observations

TMC stands for Taurus Molecular Cloud. It is a nursery of newborn stars just 430 light years away, which makes it the molecular cloud with the closest stellar nursery to Earth and, therefore, a perfect “laboratory” for study. It stands out for the abundance of complex molecules, many of them studied and/or discovered by members of the Nanocosm team.

The spectral scan has been so deep and has reached so much sensitivity that the number of molecules discovered in record time has skyrocketed. Specifically, the protagonists (which we will reveal) are anions, protonated molecules and metastable isomers.

For now, stay with the idea that the 40m antenna of Yebes, with its new receivers, surpasses everything done previously, and that the combination between the observations made with the radio antenna and the experiments carried out with the GACELA camera, which has, remember, the same receivers as the antenna, will give incredible results. It’s already giving them. The widespread enthusiasm that was breathed in the atmosphere on the day of the online chat was real and totally tangible. Because science, despite its difficulties, continues to take steps to expand our knowledge.

Originally published in Spanish on the Naukas website: “De lo nuevo y lo viejo” (2021/02/15).

Funambulist stars

Why do we study chemical equilibrium in red giants?

You may have often read that “we are stardust.” It is a rather accurate expression, especially if we think that most of the elements that make us up (this scarce 5% of the baryonic matter of the universe) emerged from the core of a star and from a whole process of death and destruction. But what do we call stardust?

Medium-sized stars (between one and eight solar masses) go through several phases throughout their lives. The longest phase is the so-called  “main sequence”, in which time is spent transforming hydrogen into helium. When hydrogen from the nucleus (where this activity occurs in principle) is depleted, the star begins to use other elements as “fuels”. This results in the star starting to “swell”, becoming a red giant and releasing its outer layers to the interstellar medium. This occurs in one of the final stages of its life, the AGB phase (from  Asymptotic Giant Branch).

A multitude of chemical phenomena take place in the atmospheres of these evolved stars, enriched by successive material dredged-up. In principle, when we talk about the birth of dust grains, we mean precisely those atmospheres of evolved stars (also supernova explosions, which are much more massive stars, but this is another story).

The layers of material released by the AGB star and forming its atmosphere are composed of a huge amount of gas molecules and a small proportion of dust grains. We are interested to know how these grains of dust are formed, from what basic elements and under what physical conditions.

To understand this whole process it is important to know the chemical equilibrium in these atmospheres, that is, the state in which, although the chemical activity continues, the chemical composition remains stable. If we know the chemical equilibrium, we will know what atoms and molecules are at the origin of the formation of dust grains (which is what we are interested in). In addition, we will have the theoretical scenario with the sequence of the different types of grains that are expected to appear as matter flows and cools from the AGB star into the interstellar medium.

In our case, in the atmospheres of AGB stars, we know that the gas is at high temperature and pressure, which is very fortunate as these are the conditions under which it is valid to use chemical equilibrium. This would be very different if we talked about, for example, the interstellar medium, where temperatures and pressures are very small and the chemical composition is given by chemical kinetics. In that case, as Marcelino Agúndez (from our group Astromol in the Institute of Fundamental Physics, IFF-CSIC) states, “it would be necessary to know the constant kinetics of a large number of reactions, in those environments everything is rather more uncertain. The interest of applying chemical equilibrium to the atmospheres of AGB stars is that, in them, temperatures and pressures are high, ergo we can use chemical equilibrium and the chemical composition can be calculated in a simple way. This has been known since the 1970s.”.

And here we get into a paper recently published by a team of researchers from the Spanish Council for Scientific Research (CSIC), focused on studying the atmospheres of AGB stars (as we said before, medium-sized stars in the final stages of their  lives).

The idea was to update all the information available so, first of all, the team compiled and updated a large dataset of thermochemical properties for 919 gaseous and 185 condensed species involving 34 elements. The chemical composition in AGB star atmospheres was calculated thanks to a recently developed code. All available information obtained from astronomical observations was also updated to, as a last step, compare the predictions of the calculations with the observations. All with the idea of reviewing what we knew so far, what our successes and mistakes were, and future prospects about molecules, molecular aggregates, and solid condensates in the atmospheres of red giant stars.

Funambulist stars, what the equilibrium tells us

This study not only tells us which aggregates could act as “bricks” of dust grains construction (and  what may be the most likely gas precursors of these grains) but even throws information on what we do not find:  potentially detectable molecules that have not yet been observed have been identified, making them good candidates for detection with observatories such as ALMA.

Finally, there are also things that don’t fit: in some cases, theoretical analysis and data don’t match. In fact, there are discrepancies of several orders of magnitude for some molecules which are observed with abundances several orders of magnitude above the expectations from chemical equilibrium. This means that, in some areas of the stellar atmosphere, there are no chemical equilibrium conditions due to unidentified phenomena that could be related to ultraviolet photons or hydrodynamic processes.

What’s new thanks to the lab

To do this type of studies it is necessary to know the thermodynamic properties of each molecular species. In the case of the most common molecules, this data is known, but for the rarest ones it is necessary to calculate or measure them.

This study has incorporated, for the first time, the properties of a large number of molecular aggregates of titanium and carbon analyzed within the Nanocosmos (ERC) project in the laboratories of the Institute of Materials Science of Madrid (ICMM-CSIC). In carbon-rich AGB stars, forecasts say the first condensates would be carbon itself, titanium carbide (TiC) and silicon carbide (SiC). (In O-rich atmospheres, the first condensate expected is Al2OR3). And it was necessary to have data on these under-studied species in order to compare them with observations.

In short, this work tells us about our mistakes and successes, about the path on which these atoms and molecules pass, about the origins of dust grains and where they are expected to appear, about the agglomeration that initiates the formation of the first solid materials from a gas of atoms and small molecules.

We are interested in how its composition can influence what happens much later, when the birth cycle of a new star begins again with the condensation of those dust grains resulting in nuclear reactions. We will continue to build knowledge on this data, relegating the wrong ones and analyzing the new information, because that’s how science works.

More information:

Scientific paper:Chemical equilibrium in AGB atmospheres: Successes, failures and prospects for small molecules, clusters, and condensates“, M. Agúndez  (IFF-CSIC), J. I. Martínez  (ICMM-CSIC), P. L. de Andres (ICMM-CSIC), J. Cernicharo  (IFF-CSIC) and J. A. Martín-Gago (ICMM-CSIC).

But… what happens in those globules?

It is not the first time we talk about Orion, nor about the molecular cloud pierced by the winds of its most massive star… but this is about molecular globules. In this constant process of destruction, something is being created.

Gallery of globules detected at the edge of the expanding Orion bubble

Those who have ever read me (poor) will say that we always talk about the same areas of space. Legendary is the series about IRC+10216 (a star and its envelope, better known as CW Leonis) published on this platform, as well as studies related to the chemistry of Orion. This is because both are magnificent “laboratories” that we can observe with relative ease (translation: these places are “close” and bright enough to observe with our telescopes). The study of these areas is aided by new and increasingly precise instruments.

On this occasion, the combination of the IRAM 30 meters telescope (in Pico Veleta, Granada) and the SOFIA stratospheric telescope (which is mounted on an airplane), helped us to discover the presence of an extremely interesting phenomenon.

But let’s take perspective…  In the Orion Nebula there is a good mess. There are massive stars (of about 8 solar masses or more) being born and emitting winds and ultraviolet radiation, which, in turn, destroys the large molecular cloud in which they were born (the one that has provided them with the material and the necessary conditions to condense). In that scuffle, an international research team has detected the presence of small molecular globules.

Expanding gas bubbles – the result of the destruction of the parent cloud – form around young massive stars because wind and radiation violently “sweep” huge amounts of the material. Ultraviolet radiation is responsible for dissociating (destroying) the gas molecules. Similar shapes had previously been found around massive stars in the Milky Way, dozens of bubbles that were detected using infrared images (let’s not forget that those environments have lots of dust and that infrared makes it easy for us to “go through” the opaque outer layers and see what happens inside). The result of this whole process is that the rate of star birth slows down, as the amount of fuel available for the formation of new stars (the molecular gas) is limited.

But there is another consequence: the presence of small globules of molecular gas on the edge of these large expanding bubbles whose existence has been a surprise: “We did not expect this discovery: one does not expect the presence of molecular gas in this kind of environment so turbulent and “sterilized” by ultraviolet radiation, but we have detected a dozen globules of thick molecular gas that have survived these harsh conditions. Most of these globules can be transiting objects that eventually fade or evaporate. But we didn’t expect this script twist.”

This is said by one of the two researchers who has led this work, Javier R. Goicoechea, from the Astromol Group at the IFF-CSIC, who goes on to describe how they are: “The globules are not massive at all, their size is approximately 200 times smaller than the Orion Nebula itself and their typical mass is around a third of the mass of the Sun. That’s why we were surprised to find out what they were hiding.”

And what has been discovered inside those globules that seemed to be just lumps? Well, scientists have discovered that one of these globules is evolving to form a very young, low-mass star. Let’s say it would be the “daughter” of the one who is riding this whole mess (the young, “angry” star, the most massive in the Trapezium cluster, Orionis C, located at the center of the Orion Nebula).

The importance of the movement

To understand what was happening within the great Orion bubble there are several important parameters that until now had been difficult to obtain: knowing how it moves, what forces drive its expansion and what its chemical composition is. Thanks to the combination of the data obtained with these two facilities, the team has obtained the first images that solve the speed of the gas and show the properties of this bubble of 10 light years in size that is suffering the wrath of Orionis C, since the bubble expands at almost 50,000 km / h, providing its peculiar appearance to the iconic region that we know as “the sword of Orion”.

This information has been obtained thanks to the analysis of the emission of gases produced by molecules of carbon monoxide (CO) as well as positively charged carbon atoms (ionized carbon or C+, analyzed in the work led by Cornelia Pabst, of the University of Leiden, The Netherlands).

As the authors of these works state, “It is not yet clear whether these small objects can be a source of very low-mass stars, brown dwarfs, or planetary-mass objects. We have captured the first glimpses of the star-forming processes that are taking place within one of these small globules.”

The team hopes to be able to carry out more observations of the emission of other molecules (more sensitive to the presence of more dense gas inside the globules) to clarify their future and fate. Will they evaporate in the long run or, conversely, will they evolve into a nursery of newly formed stars?

Technical information:

This work is part of an international collaboration that leads two major complementary observation programs. One uses the 30-meter IRAM telescope in Pico Veleta, Spain (Dynamic and Radiative Feedback of Massive Stars, PI: J. R. Goicoechea) to map the emission of 12CO, 13CO and C18O (J=2-1) at a resolution of 11 arcseconds; the other uses NASA/DLR’s SOFIA airborne observatory (C+ Square-degree map of Orion, PI: Prof. A. G. G.M. Tielens) which has produced the largest map of the [CII]158 μm line (usually the brightest line in the neutral interstellar medium) at a resolution of 16 arcseconds. These Orion C+ images are also relevant as a local model in the extragalactic context as the ALMA and IRAM-NOEMA radiointerferometers can detect the emission of [CII] 158 μm from galaxies with very distant star formation (with high redshift).

The consortium consists of the following institutions: CSIC, University of Leiden, University of Cologne, IRAP-CNRS, IRAM, Max-Planck Institute for Radio Astronomy, ESAC, NASA Ames and University of Maryland.

The scientific articles related to this work are:

J. R. Goicoechea, C. H. M. Pabst, S. Kabanovic, M. G. Santa-Maria, N. Marcelino, A. G. G. M. Tielens, A. Hacar, O. Berné, C. Buchbender, S. Cuadrado, R. Higgins, C. Kramer, J. Stutzki, S. Suri, D. Teyssier, and M. Wolfire. Molecular globules in Orion’s Veil bubble. IRAM 30 m 12CO, 13CO, and C18O (2-1) expanded maps of Orion A. Accepted for publication in Astronomy & Astrophysics (2020).

– C. H. M. Pabst, J.R. Goicoechea, D. Teyssier, O. Berné, R.D. Higgins, E. T. Chambers, S. Kabanovic, R. Güsten, J. Stutzki, and A.G.G.M. Tielens: Expanding bubbles in Orion A: [CII]158μm observations of M42, M43, and NGC 1977. Accepted for publication in Astronomy & Astrophysics (2020).


Images of the Orion Nebula (M42). The left panel shows the emission of positively charged carbon atoms, observed with SOFIA, revealing a huge bubble pushed by the winds of the most massive star in the Trapezium cluster. The 12CO and 13CO images, taken with the 30-meter IRAM telescope, show the molecular gas in the cloud in which stars are forming, behind the bubble. The # numbers show the position of some of the detected globules at the edge of the bubble. Credits: Goicoechea et al. (2020).

Gallery of globules detected at the edge of the expanding Orion bubble. The reddish colors represent the emission of carbon monoxide molecules detected with the 30-meter IRAM telescope. The bluish color is an infrared image obtained by the Spitzer Space Telescope. The #1 globule coincides with the position of a very young, low-mass star. The white circle represents the angular resolution of the IRAM telescope 30-meters, approximately several times the size of the Solar System. Credits: Goicoechea et al. (2020).

Originally published in Spanish on the Naukas website: “Pero… ¿qué pasa en esos glóbulos?” (2020/07/02).

L483 Trilogy (Part Three) – Where do you hide, Dicyanopolyyne?

Interstellar isocyanogen (CNCN) discovered

This is the third and final part of a trilogy in which we have unveiled several new molecules discovered in our L483 dark cloud. In the first part, it was the HSC and HCS isomers; in the second part, NCO; and today we close with the CNCN: that is, carbon everywhere.

It is true that interstellar chemistry is essentially organic. About three-quarters of the nearly 200 molecules detected to date in the interstellar and circumstellar medium contain at least one carbon atom. Among them there are alcohols, aldehydes, acids,  ethers and amines, but the most frequent functional group is that of nitriles, which contain a group of cyanide –CN. In fact, the strong bond of this group is present in more than 30 interstellar molecules, although, until recently, no molecule containing two cyano groups (dinitrile) had been observed in interstellar space.

We have already talked before about cyanogen (NCCN), that lethal gas for humans indirectly detected in our protagonist dark cloud, L483, in 2015 (see the article “Cyanogen: a poison, a comet and a jedi story”, where we talked about the protonated cyanogen, NCCNH+.) In this new study, the isocyanogen CNCN, which is a polar and metastable isomer of the cyanogen [1] has been detected for the first time in space (in the same cloud).  

The detection of CNCN in the interstellar medium reinforces the long-held idea that cyanogen is the main precursor to cyanide (CN) that has been observed for decades in many comets. In fact, recently the Rosetta mission  has detected cyanogen in comet 67P.

Cyanogen is the simplest member of the family of dicyanopolyynes, consisting of a highly unsaturated linear skeleton of carbon atoms topped by a cyano group at each end, i.e., N≡C−(C≡C)n−C≡N. They are stable molecules and the authors of this work that closes our L483 trilogy have deduced that, in interstellar clouds, these molecules with two cyano groups (such as NCCN) are probably as abundant as molecules with a single group –CN  (as HCN)  [2].

And why do we have to go around deducting? Can’t we see them directly? Well, that’s the point. The problem in detecting certain species in the interstellar medium (among them, the dicyanopolyynes) is that they do not leave “footprint” because they are not  polar.

As we said in the second part of this trilogy, the more polar a molecule is, the more intense the lines. Therefore, if a molecule has low polarity the lines will become weaker and detecting them will be more complicated.

In this particular case everything is even more complicated, since there is no way to detect the dicyanopolyynes because they are totally apolar. Therefore, having no rotational spectrum, it cannot be observed by radioastronomical techniques. But there are other ways to deduce their presence.

For example: in the carbon-rich envelope IRC+10216 (which we have also talked about a lot for its diva complex), the presence of NCCP – a chemical cousin of the cyanogen in which an atom of N is replaced by an atom of P – was tentatively identified. Therefore, it is reasonable to think (although we cannot observe them) that the dicyanopolyynes can be abundant in molecular clouds.

To investigate the plausibility of this hypothesis, it was proposed that the presence of NCCN in interstellar and circumstellar clouds can be indirectly tested through the observation of chemically related polar molecules, a hypothesis that has been confirmed with the detection a few years ago of protonated cyanogen (NCCNH+) and the discovery of the new member of the family, CNCN.

The isocyanogen CNCN

At this point in our trilogy, we see that, to deduce the presence of a molecule indirectly, we have to use a multitude of tools: chemical models that we are perfecting, better detectors and instruments in our radio telescopes and, therefore, more sensitive observations of the areas we are studying.

While the presence of NCCN in interstellar clouds seems undoubted due to the detection of NCCNH+ and CNCN, their abundance remains difficult to define due to the little knowledge about the chemistry that relates to these species. To further know the chemistry of dicyanopolyynes in space it will be necessary to carry out experiments and theoretical studies of some key reactions, in addition to astronomical observations of high sensitivity. It seems we have to keep looking at and interpreting the data from these regions.

Concerning the dark cloud L483, it has revealed some of its secrets in the survey that has given rise to this trilogy, based on several scientific publications with associated discoveries that are cementing a path on which to continue asking us, if it does, “Where do you hide, dicyanopolyyne?”.


[1] It has also been tentatively discovered in TMC-1, the taurus molecular cloud.

[2] It is estimated that the abundance of NCCN in relationto H2 may be of the order of between 10−9–10−7, similar to that of HCN.

More information:

Discovery of Interstellar Isocyanogen (CNCN): Further Evidence that Dicyanopolyynes Are Abundant in Space“. M. Agúndez, N. Marcelino and J. Cernicharo (Institute of Fundamental Physics, CSIC, Spain).

A sensitive λ 3 mm line survey of L483. A broad view of the chemical composition of a core around a Class 0 object“. M. Agúndez, N. Marcelino and J. Cernicharo (Institute of Fundamental Physics, CSIC, Spain), E. Roueff (Paris Observatory, Sorbonne University, PSL University, CNRS, LERMA 2), and M. Tafalla (National Astronomical Observatory, OAN-IGN, Spain).

Based on observations carried out with the IRAM 30 m radio antenna.

Image: Image of the L483 region captured by NASA’s Spitzer Space Telescope. The circle points the area studied with the IRAM 30m radio telescope and published in the article “A sensitive λ 3 mm line survey of L483. A broad view of the chemical composition of a core around a Class 0 object’.

Originally published in Spanish on the Naukas website: “¿Dónde te escondes, dicianopoliino? Trilogía de L483 (Tercera parte)“. (2019/07/22).

L483 trilogy (Part Two) – Put a radical in your dark cloud

Detection of the NCO radical in space

This is what the L483 dark cloud looks like if we don’t use radio astronomy

In the first part of this series we talked about the sulfur lost in L483. But in the studies carried out in this dark cloud, much more has been discovered. Among them, the first detection in space of the isocyanate radical (NCO) with a significant abundance.

Studying the observations of L483 carried out with the IRAM 30m radio telescope, it was seen that there were bright carbon chains such as C4H, which suggested that the region could host a propitious environment to carbon chain chemistry [1].

Why are carbon chains important? Most molecules observed in space can be formed only with atoms of hydrogen (H), carbon (C), nitrogen (N) and oxygen (O). These atoms are the pieces for building organic and prebiotic molecules and, together, constitute the backbone of the peptide bond that binds two amino acids and allows the construction of long proteins. Therefore, the observation of simple molecules with the C(=O)–N group in space can provide important clues about the first chemical steps in amino acid synthesis, considered key in all biological processes.

The isocyanate radical precisely consists of a C(=O)–N structure and is therefore the simplest molecule that houses the base scheme of the peptide bond. It has efficient formation mechanisms but, although it is predicted (from what the models tell us) that it must be abundant in dark clouds… its abundance is small, which complicates its detection. In addition, it has a low polarity (the higher the polarity, the more intense the lines of the molecule) [2] so the observed lines are weak. To this must be added the “noise” (which will depend on the observation time and the sensitivity of the instrument).

We usually use the metaphor of the field of grass that does not let you see the flowers: our field of herbs (the noise) will be reduced the higher the quality and sensitivity of our observations, letting us distinguish the “flowers”, which would be the lines of the molecules.

Technological advances are enabling us to make progress in this direction. Increasingly sensitive detectors are being built, which makes the noise less. In addition, in this work a deep survey has been carried out that has allowed us to observe in more detail, providing many unexpected results (which we will continue to talk about in the third part of this trilogy, what did you think, that we were going to tell you at once? Well, no).

How the NCO is formed

When talking about “zones” or regions in a certain environment of space, we must clarify that there is no uniformity in the conditions that give rise to the chemistry of these places. In fact, recent observations carried out with the ALMA interferometer  have demonstrated a chemical differentiation in L483, which has carbon chains such as C2H that trace the envelope, and more complex organic compounds distributed around the protostar, that is, in these two areas different physical and chemical phenomena are occurring that give rise to a different chemical richness.

The detection of NCO (carried out with IRAM 30m) has taken place in the envelope of the low mass protostar in L483, and with this information it follows that the chemical processes for the formation of NCO are mainly two: one is from the reaction between CN and O2 and another would be by the recombination of the ion H2NCO+, which has also been detected in this work, thus supporting the formation of NCO by this route.

One of the important aspects of taking steps in the discoveries of new molecules is that the chemical models are updated, in this case, those related to NCO: taking into account the uncertainties in the model, the observed abundances are reproduced relatively well, which indicates that we are on the right track.

But there is still much to study. Although the survey has been of incredible sensitivity, “The next step -says Nuria Marcelino, lead author of this paper- would be to carry out NCO observations on sources that are at different stages of the star formation process. This could help us understand its role in the prebiotic chemistry of space.”

With this survey –she continues– we have revealed the chemical richness of L483, discovering several species that had not been detected before and confirming others that had been detected tentatively. Finally, we have been able to see the flowers among the grass.”

But, friends, there are still many flowers to be revealed. We’ll look at some of them in the next part of this L483 trilogy.


[1] Apart from carbon chains, L483 is also rich in oxygen-carrying organic molecules    such as HCO, HCCO, H2CCO, CH3CHO, HCCCHO and c-C3H2O.

[2] Polarity has to do with the distribution of the electric charge in the molecule. The more asymmetric the charge distribution, the more polar the molecule. The main implication of this is that, the more polar a molecule is, the more intense the lines. Therefore, as far as the NCO is concerned, the low polarity makes the lines weak, making it difficult to detect them.

More information:

This work has been published in the paper Discovery of the elusive radical NCO and confirmation of H2NCO+ in space“, A&A 612,L10  (2018). By N. Marcelino, M. Agúndez, J. Cernicharo (Instituteof FundamentalPhysics, CSIC, Spain), E. Roueff (Sorbonne University, Paris Observatory, CNRS, France) and M. Tafalla, (National Astronomical Observatory, IGN, Spain). Based on observations carried out with the IRAM 30m radio telescope.

Image: This is what the L483 dark cloud looks like if we don’t use radio astronomy. Credit:  NRAO/Gary Fuller. https://www.cv.nrao.edu/~awootten/l483/l483.html

Originally published in Spanish on the Naukas website: “Pon un radical en tu nube oscura. Trilogía de L483 (Segunda parte)” (2019/06/26).

L483 trilogy (Part One) – In Search of Lost Sulphur

First identification of two species in space, HCS and HSC

Image of the L483 region captured by NASA’s Spitzer Space Telescope

Over the past few decades, various research teams working to study different areas of space have had the same question: where is the missing sulfur? This is what happens, for example, with the study of some protoplanetary disks  and interstellar clouds. That is because sulfur chemistry outside the Earth, especially in the dark and cold clouds, on which we will focus today, presents some unknowns such as the detection of less sulfur than expected.

Sulfur in the gas phase can be found as part of different molecules (called sulfur “carrier” species).  However, these species are less than 0.1% of the estimated cosmic abundance of sulfur for dark clouds, that is, only a tiny amount of what is supposed to be there has been detected.

The case of HCS and HSC in the cold cloud L483

The team led by Marcelino Agúndez, Ramón y Cajal researcher at the Institute of Fundamental Physics of the CSIC, who is among those looking for “lost sulfur”, detected two new molecules carrying sulfur: the HCS radical and its less stable isomer, HSC. They identified them in the dense cloud L483, a source with a very rich chemistry and where new molecules from other families (such as  HCCO, NCCNH+ and  NS+) have also been discovered.  

L483 is a molecular cloud, located in the Aquila Rift, which houses the IRAS 18148-0440 protostar. This protostar is in full transition, going from being a protostar of class 0 to class I, that is, the dust and gas around it are taking the form of a disk and begin to distinguish its layers (although it does not yet have reactions in the core, that will come after going through phases II and III, after which it will end up being a full-right star).

The presence of the protostar in L483 involves a great deal of activity, with material from the cloud falling by gravity on it, fattening it, as well as a powerful jet of matter emanating from it, taking away much of the angular momentum and favoring the process of star formation. Given the environment, there should be a lot of sulfur, so it must be identified among the observations’ data.

The sulfur molecules discovered, HCS and HSC, are not abundant enough to explain the problem of lost sulfur, but their detection has revealed several peculiarities about how sulfur chemistry works in interstellar clouds. Since sulfur is in the same column of the periodic table as oxygen, both elements are considered to have similar chemical properties. However, the detection of HCS and HSC has revealed that sulfur and oxygen chemistry behave significantly differently than expected. Let’s see why.

To understand this we can compare the abundances of sulfur molecules with those of their oxygen analogues. That is, if we talk about the molecule with hydrogen, carbon and sulfur (HCS), its analog with oxygen is HCO (hydrogen, carbon and oxygen). In this way we can compare the relative abundances of the species carrying sulfur H2CS /HCS (being H2CS the stable form and HCS the unstable radical) with the relative amounts of H2CO /HCO.

The result is that in L483, H2CO (formaldehyde) is ten times more abundant than HCO (formyl radical). But in the case of its sulfur analogue the same does not happen, since H2CS (Thioformaldehyde) is as abundant as HCS. In addition, in L483 HCS is even more abundant than HCO, which is surprising, given that oxygen is more abundant than sulfur in the cosmos.

On the other hand, the metastable isomer HSC is found with a low abundance, while its oxygen analogue HOC has not yet been observed in space, mainly because there is a total lack of experimental information about this species (it has not been possible to characterize it in laboratory experiments).

Delving a little into the title of this report, we wonder, again, where is the sulfur that we don’t see. It is interesting to note a recent study, by Vidal et al., “On the reservoir of sulphur in dark clouds: chemistry and elemental abundance reconciled“, which    concludes that most of the sulfur in dark cold clouds should be in the form of H2S and SH ice on the surface of dust grains.

This study also indicated that, to detect HCS in gas phase, it would be necessary more than a thousand hours of observation with the IRAM 30 m telescope, concluding that it was difficult to locate HCS in gas phase in dark and cold clouds. However, this work, in the words of Agúndez, “shows that, although there are many unknowns to be solved, we have managed to detect the presence of HCS with much fewer hours of observation“.

Then, where is the sulfur missing from the dark, cold clouds? It is possible that sulfur is deposited only on dust grains, although it is not clear how.  Part of it could get trapped in the core of the grains as refractory compounds and another part could be in the form of ice. Although it is also possible that molecules of the gas phase that have not yet been identified may contain a significant amount of sulfur. It may even be in atomic form.

So, we assume that sulfur is there, but we haven’t been able to detect it yet with our instruments. On the other hand, studies of this region have not only revealed its “lack” of sulfur… but that will be in the next chapter of this trilogy about L483, the dark cloud that has so many things to reveal about the chemical complexity of the universe.

More information:

This work has been published in the paper “Detection of interstellar HCS and its metastable isomer HSC: new pieces in the puzzle of sulfur chemistry”,  A&A 611, L1 (2018). By M. Agúndez, N. Marcelino, J. Cernicharo  (Institute of Fundamental Physics, CSIC, Spain)  and M. Tafalla, (Observatorio Astronómico Nacional, IGN, Spain). Based on observations carried out with the IRAM 30m Telescope.

IMAGE: Image of the L483 region captured by NASA’s Spitzer Space Telescope. http://www.spitzer.caltech.edu/images/3132-sig10-006e-Protostellar-Envelope-and-Jet-L483

Originally published in Spanish on the Naukas website: “En busca del azufre perdido. Trilogía de L483 (Primera parte)” (2019/06/18).

Star eats cloud (or “In Orion it’s no time for joking”)

Getting data from a telescope can be very exciting. Basically, because getting them and interpreting them is a whole process that can take several years… Since the observation program is designed, the time is requested, it is granted (or not), the observations are carried out, the data is obtained and, finally, the information is analyzed and extracted… the whole process is a marathon full of uncertainty and challenges.

Image 1: Red-green-blue image showing three different velocities of the gas associated with the heart of the Orion cloud.

Of course, it can be data from a ground-based telescope or a space telescope.

Or, as in our case, it can be both.

SOFIA: Ground or space telescope? Well, both!

We’re talking about a telescope installed in a modified NASA Jumbo 747 aircraft. It is called SOFIA (Stratospheric Observatory for Infrared Astronomy) and, at each observation, it takes flight to the stratosphere, about 13 km above sea level (a couple of km above commercial flights) and goes back down, perching at its Californian airport and returning home to rest.

Each observational flight lasts about 10 hours, and the data obtained are very important, among other things because, right now, there is no instrument outside the Earth (that is, above the atmosphere and its nefarious turbulence) that observes in the far infrared, a range of the electromagnetic spectrum critical to understand how stars form and interact with the interstellar medium.

With a mirror of 2.5 meters in diameter, SOFIA is the name of the whole set. And Javier R. Goicoechea says (I will introduce him in a moment) that it is impressive to see how the whole plane can tremble from the turbulence while the intelligent hydraulic structure that supports the telescope and its instruments compensates for those alterations and remains perfectly still (I would love to change myself for the instrument, I want one of those compensators for my air trips).

Image 2: SOFIA (The Stratospheric Observatory for Infrared Astronomy)

SOFIA is 80% NASA (which has built and operates the observatory) and 20% DLR (the German space agency).

For starters, getting a plane to fly with an impressive door open (yes, you read that right, open), is already quite a feat. That it does so, in addition, with a team formed by telescope and instrument of about 20 tons of weight, also has its complications.

But let’s get to deeper.

It turns out that Javier R. Goicoechea, senior scientist at the Institute of Fundamental Physics (IFF) of the CSIC, participates in an international team that studies the destructive effects of ultraviolet radiation and the strong winds emitted by young massive stars in the interstellar clouds where they are born. Last year the team obtained 10 observation flights in order to map the Orion cloud in the emission of ionized carbon, the brightest emission from interstellar gas. As he states, “SOFIA is like a space telescope, in the sense that it allows us to observe in the infrared above 99% of atmospheric water vapor, but after a night of observations, astronomers and telescope land on the ground to regain strength.”

Image 3: Javier R. Goicoechea (IFF-CSIC) in full flight and data collection. In the background is Jürgen Stutzki (University of Cologne, Germany), co-Principal Investigator of the GREAT instrument.

The results have been really amazing.  

WHAT A PROGENY! Daughters eating parents.

As we have told in other articles, dense clouds of gas and dust are the birthplace of the most massive stars in the galaxy. The mass is concentrated, condensed, the reactions begin in the nucleus and… A star is born!

The more mass the star has, the more violent it is and the less time it will live. The fact is that we know that, in this area of Orion, there are very massive stars -the Trapezium cluster- that are “sweeping” the surrounding material, undoing the cloud that saw them born with their powerful stellar winds and their intense ultraviolet radiation. A kind of “parentophagy” (I know this word does not exist…).

The data obtained with SOFIA have revealed that this happens much earlier than previously thought. In just a few hundred thousand years the winds coming from the most massive star of the Trapezium have pierced the natal cloud, creating a huge bubble, whose expansion and movements have been revealed thanks to the 3D observations obtained (have I not said that an amazing 3D film has been made with the data?). A single star giving shape to one of the most observed and known regions of the sky.

What a blow.

Measuring speeds for the first time

The results obtained have given, for the first time (yes, we always say that because it is very cool in astronomy to say “as never before”, “for the first time”, “with an unprecedented resolution”, and again and again)… For the very first time a 3D map of the gas velocities in the studied area has been made. Thanks to the spectroscopy of very high spectral resolution, maps of the speed of the expanding gas bubble have been obtained, resulting in this amazing video:

In short. Everything is going faster than predicted, in every way. The young massive stars determine, much earlier than previously thought, the shape and evolution of the interstellar environment that saw them born, ravaging and cleaning, with their strong stellar winds, the entire region that surrounds them. That means they sweep away the interstellar material needed for the formation of new stars.

For Javier R. Goicoechea, “It is incredible that after more than 400 years observing the great Orion Nebula, we have now been able to understand that the winds coming from the most massive stars blow the surrounding cloud and give it that morphology so recognizable“.


Image 1: Red-green-blue image showing three different velocities of the gas associated with the heart of the Orion cloud. The wind from the most massive stars has created a bubble (in black) and prevents the formation of new stars in its environment. At the same time, the wind sweeps the gas from the edges (in color), creating a shell of thin gas around the bubble and where perhaps a new generation of stars can form. Credits: NASA/SOFIA/Pabst et al.

Image 2: SOFIA (The Stratospheric Observatory for Infrared Astronomy) flying over the California sky. The telescope can be seen inside the open cavity at the rear of the aircraft. Credit: NASA/Jim Ross

Image 3: Javier R. Goicoechea (IFF-CSIC) in full flight and data collection. In the background is Jürgen Stutzki (University of Cologne, Germany), co-Principal Investigator of the GREAT instrument.

More information:

Paper: C. Pabst, R. Higgins, J.R. Goicoechea, D. Teyssier, O. Berne, E. Chambers, M. Wolfire, S. Sury, R. Guesten, J. Stutzki, U.U. Graf, C. Risacher, A.G.G.M. Tielens. Disruption of the Orion Molecular Core 1 by the stellar wind of the massive star Ɵ1 Ori CNature. DOI: 10.1038/s41586-018-0844-1.

CSIC Press Release (in Spanish):  Los vientos estelares de las estrellas masivas dan forma a la nebulosa de Orión

Link to the SOFIA press release with 3D videos

Hydrocarbons open bar in Orion

Orion’s skin

New observations of the Orion B nebula reveal the anatomy of a star-forming reservoir

Originally published in Spanish on the Naukas website: Estrella come nube (o «En Orión no está el horno p’a bollos») (2019/01/14).

Molecular detectives

The discovery of the new NS+ cation, present in numerous astrophysical environments, confirmed with laboratory spectroscopy

NS+. Credits: KIDA, Kinetic Database for Astrochemistry.

A team of researchers, led by José Cernicharo (IFF-CSIC) has announced the detection in space of a new molecular species, identified from astrophysical data obtained with observations carried out with the IRAM 30m telescope.

Although nitrogen sulfide  (NS) was first detected in space in 1975, the presence of its NS+ cation had not been discovered until now. A cation is an atom or molecule with a positive electric charge because it has lost electrons from its original endowment. In the case of  NS+, the chemical models applied in this work indicate that it is formed by the reactions of the neutral atom N with the cation SH+ and that of the neutral atom S with the cation NH+.

The interesting thing about this work is not only the first detection of NS+ [1], but the discovery of its ubiquity and its presence in most astrophysical environments: it  has been detected in cold and faint molecular clouds where there is still no activity of star formation, in somewhat denser clouds where matter begins to collapse and prestellar nuclei begin to be seen, and in clouds that are authentic stellar nurseries, where violent processes due to ultraviolet radiation from young stars and to jets of material ejected by the protostars  [2] are already taking place.

A detective work confirmed in the laboratory

The gaseous phase chemistry of cold and dark clouds is mainly based on the reactions between ions (electrically charged molecules) and neutral molecules. However, ions (positively charged cations, or negatively charged anions) represent only a small percentage (about 15%) of the molecular species detected.

But if NS+ is present in so many astrophysical environments, why wasn’t it identified before?

Since astrochemistry has increasingly precise tools, we often talk about spectra with “forests of lines”, a deep collection of overlapping data that is difficult to discriminate. Where does one molecule end and another begin? If they have never been characterized before, if they have not been studied and checked against laboratory data or if their possible presence has not been theorized, it is very likely that they will remain anonymous, sometimes before our eyes.

In the words of José Cernicharo (Institute of Fundamental Physics, CSIC),“The detection of NS+ was a real work of “molecular detectives”. When we realized that in that observational data there was a pattern that was repeated, we started a search in which, first, we discarded various candidates.”  

An in-depth understanding of how molecular spectroscopy works and interstellar chemistry were the tools that led the team to determine that the NS+ cation is the species most likely responsible for producing the lines found.

On the other hand, in astrochemistry there is a lot of laboratory effort whose purpose is to validate the results of the theoretical models and the data observed with the telescopes (in this case the IRAM 30m antenna, in Pico Veleta, Granada). To confirm that it was possible for NS+ to be in so many different environments, the “Laboratory of Atoms, Molecules and Lasers Physics” (CNRS and  University of  Lille, France) carried out several experiments to reproduce NS+.

The information obtained, applying spectroscopy techniques, corroborated full coincidences with both observational data and theoretical models: they had found a new molecular species in space.


[1] The NS+ cation has been completely characterized through three rotational transitions, one of them with hyperfine structure, distinctive of a molecule with an atom with spin 1.

[2] Although present in a wide variety of environments, it is apparently not in others such as, for example, the hots cores of  Orion-KL or the evolved star IRC+10216.

More information:

This work has been presented in the paper Discovery of the ubiquitous cation NS+ in space confirmed by laboratory spectroscopy and its authors are  J. Cernicharo  (Molecular Astrophysics Group (ICMM-CSIC)/Molecular Astrophysics Group, Department of atomic, molecular and surface processes (IFF-CSIC), Spain);  B. Lefloch  (University Grenoble Alpes, France); M. Agundez  (Molecular Astrophysics Group (ICMM-CSIC)/Molecular Astrophysics Group, Department of atomic, molecular and surface processes (IFF-CSIC), Spain);  S. Bailleux (Laboratory of Atoms, Molecules and Lasers Physics, CNRS, University of  Lille, France); L. Margulès  (Laboratory of Atoms, Molecules and Lasers Physics, CNRS, University of  Lille, France); E. Roueff (LERMA, Paris Observatory, PSL Research University, CNRS, University of The Sorbona, France);   R. Bachiller  (National Astronomical Observatory (OAN, IGN), Spain); N. Marcelino  (Molecular Astrophysics Group (ICMM-CSIC)/Molecular Astrophysics Group, Department of atomic, molecular and surface processes (IFF-CSIC), Spain); B. Tercero  (Molecular Astrophysics Group (ICMM-CSIC)/ National Astronomical Observatory (OAN, IGN), Spain); C.  Vastel (IRAP, University of Toulouse, CNRS, UPS, CNES, France); E. Caux (IRAP, University of Toulouse, CNRS, UPS, CNES, France).

Originally published in Spanish on the Naukas website: “Detectives moleculares” (2018/02/12).

The big yellow void…

… and the loss of mass of the yellow hypergiant star IRC+10420

Why is there a seemingly empty area of the Hertzprung-Russell diagram? And why is it called a “yellow void”? And, while we are ai it… what is the Hertzprung-Russell or H-R diagram?

Image1: IRC+10420. Yellow hypergiant star IRC+10420 surrounded by ejected material. Credit: Roberta M Humphreys.

First of all, welcome to a report that is going to be totally yellow (but not yellow press, we leave that to IRC+10216).

I’m going to take it for a fact that you have no idea about astronomy. (If you already know what the H-R diagram is, you can go to the next heading: ‘The “yellow empty” area’).

The Hertzsprung-Russell diagram (yes, I know you can search for it on Wikipedia, but I’m going to explain it to you anyway) is a way to visually illustrate a set of star-related data, so that we can understand its distribution according to certain parameters. There are many types of diagrams, but the one that Hertzprung and Russell invented independently makes us see the distribution of the stars according to their brightness and temperature. It’s like taking all the stars in the Milky Way – imagine a bunch of colored marbles – and put them in a box distributed according to those parameters. We would see them classified into a single image, giving us an idea of how many of them are in each class.

Well, there’s supposed to be something yellow in one part of that box… And there isn’t.

The “yellow empty” area

In the H-R diagram there are two regions that have very few stars: the ‘Hertzsprung Gap’ and the Yellow Void.  In the first, it is believed that the problem is that stars have not yet been observed at that stage because it is a rapid stage in the life of a solar-type star; in the case of yellow void, it is believed that there should be yellow hypergiants, but there is none.

Yellow hypergiant stars are a type of evolved massive star that have extreme initial masses and very high luminosities [1]. In fact, they are supposed to end up exploding as supernovae after going through several phases in which they lose a lot of mass.

The thing is these stars are very unstable. When, by the evolution of their characteristics (specifically, by the changes in their effective temperature), they are about to enter the ‘yellow void’ area of the diagram, they “bounce” and go back to an area where they appear as red… But how on Earth! What’s wrong with yellow hypergiants? Why don’t they step into that empty area (there is so many space!)?

Image 2: The yellow void. Illustration of the hypergiant star HR 8752 through the yellow void. The diagram shows the surface temperature of the star observed in the last 100 years. It increased from ~5000 to ~8000 degrees between 1985 and 2005, while the radius decreased from 750 to 400 times the radius of the Sun. Credit: A. Lobel ROB.


There are two types of yellow hypergiant stars. The first are stars that are starting to age after finishing their main sequence, moving to the red supergiant phase (i.e., they do not yet have an envelope created by matter that they release into the environment when they start “dying”).

But our yellow hypergiants are of the second type, evolved stars with envelopes and large mass loss that go from the yellow supergiant phase to the WR (Wolf-Rayet) star phase. Afterwards, they will move to the blue luminous variable star stage, then to hydrogen-poor WR star and eventually explode like supernovae (to see it very clearly, go to  “Stellar Evolution”  of @molasaber).

IRC+10420 is a prototypical yellow hypergiant (located in the Aquila Constellation) that has already passed the red supergiant phase (in which they can lose up to half of their initial mass) and has evolved to higher temperatures in the H-R diagram [2].

The yellow void stage results in a series of episodes of mass ejection that occurs in the form of bursts. As a result, the star is surrounded by dust, so perhaps what is happening is that we cannot measure one of the parameters of the H-R diagram correctly because the effective temperature of the star, that is, the temperature of its detectable surface… can’t be detected!

Our yellow hypergiant is hidden behind the dust, so we see her as a reddish star. But the actual effective temperature continues to rise and a pseudo-photosphere that keeps them at the low temperature limits of the yellow void in the HR diagram is formed around the yellow hypergiant stars. As the ejected material is diluted in the outer area, we induce that at the end they will appear just beyond the high temperature limit of the yellow void. That’s why they look like bouncing off the diagram!

Therefore, the evolution of yellow hypergiants remains hidden until they become what has been called slash stars [3]  (renamed by myself as oldyoung stars) and eventually enter the Wolf-Rayet phase.

The rich chemistry of this yellow hypergiant star

There is something important to keep in mind: these stars are aging, they are losing mass at an extremely high rate, they are ejecting matter to the medium at an incredible speed… [4] And all that matter is the one that feeds back the interstellar medium. Here we get to the heart of the matter: what we are interested in is knowing more about the chemical properties of circumstellar matter ejected by the most massive evolved stars. And studying their behavior helps us better understand the processes that occur before supernova explosions and determine when different species of molecules are formed.

Using the IRAM30m telescope, a team of astronomers, leaded by Quintana-Lacaci (CSIC), did an IRC+10420 probe confirming that the chemistry of this object is especially rich: they detected 22 molecular species in the circumstellar envelope of this object [5].

Although it is predicted that the mass ejections are huge in these objects, only three yellow hypergiants, IRC+10420, AFGL 2343 and IRAS 17163-3907, have shown molecular emission.

The expulsion of this material may also be explained in a similar way to that of ejections that take place in low-mass AGB stars, the small counterpart of massive stars, which also age by ejecting matter but do not end up bursting as supernovae. In this case, mass ejection is driven by radiation pressure in dust grains.

But this is not all: the ejections prior to the yellow hypergiant phase… are no longer part of the envelope around them. For Quintana-Lacaci “All the molecular material we observe had to be expelled only during the yellow hypergiant phase. Any gas expelled during the previous phase of red giant star would have been rapidly diluted in the interstellar medium and would have been photodissociated by the ultraviolet radiation of the interstellar medium”.

Which means that there may be no stars in the “yellow void” of the diagram because they hide behind the dust they have recently ejected, while the dust they ejected in previous episodes has already become part of that interstellar medium composed of dust grains (1%) and gas (the remaining 99%).

Behold, we have a possible answer to that yellow void. Along the way, we seem to have learned things about huge stars who like to play hide-and-seek, hiding behind layers of dust and leaving an “empty space” in our knowledge. A void we strive to fill.


[1] This one in particular has a brightness of L ~ 5 × 105L⊙ and an estimated initial mass of Minit ~ 50M⊙.

[2] In particular, the spectral type of IRC+10420 has changed from F8Ia (with an effective temperature of 6300K) to A5Ia (8300K) in just 20 years.

[3] Slash stars are massive, hot stars that have typical characteristics of both old stars (in this case Wolf-Rayet) and young stars (type O). Slash comes from the “/” symbol that is used to separate young star characteristics from old star characteristics (as happens, for example, in Ofpe/WN9 stars). I mean, they’re  oldyoung stars.

[4] In particular, for the IRC+10420 yellow hypergiant, they detected a separate circumstellar envelope with an extension of 5×1017cm expanding at speeds of ~37 km/s. There are two episodes of strong mass ejection responsible of the formation of this circumstellar envelope, which occurred within 1,200 years and reached a mass loss rate of 3 ×10−4M⊙ yr−1.

[5] The team has conducted a survey of IRC+10420 at wavelengths of 1 and 3 mm, identifying 106 molecular emission lines from 22 molecular species: CO,  13CO, CN, H13CN, HCN, SiO, 29SiO, SO, SiS, HCO+,CN, HNC, HN13C and CS.

More information:

Paper “A λ 3 mm and 1 mm line survey toward the yellow hypergiant IRC +10420: N-rich chemistry and IR flux variations”, by G. Quintana-Lacaci (ICMM-CSIC), M. Agúndez (ICMM-CSIC), J. Cernicharo (ICMM-CSIC), V. Bujarrabal (OAN-IGN), C. Sánchez Contreras (CAB/INTA-CSIC), A. Castro-Carrizo (IRAM France), and  J. Alcolea (OAN-IGN).


Image1: IRC+10420. Yellow hypergiant star IRC+10420 surrounded by ejected material. Credit: Roberta M Humphreys.

Image 2: The yellow void. Illustration of the hypergiant star HR 8752 through the yellow void. The diagram shows the surface temperature of the star observed in the last 100 years. It increased from ~5000 to ~8000 degrees between 1985 and 2005, while the radius decreased from 750 to 400 times the radius of the Sun. Credit: A. Lobel ROB.

Originally published in Spanish on the Naukas website: “El gran vacío amarillo… (2017/10/30).

Baby, baby, baby, light my way

Yes, may be this reminds you the lyrics of “Ultraviolet”, a song from U2 that fits perfectly with our topic. Let’s sing some astrochemistry.

Image 1: Orion Nebula.

The world of science often says that space is hostile, that it is very difficult to find complex molecules (even if there are). The fact is that one of the culprits of breaking bonds between atoms and leaving everything broken is ultraviolet radiation from stars, and in this case, the distant ultraviolet. But also, like Ying and yang, it may be responsible for liven up certain organic molecules.

Astrochemistry looks for those molecules and study their endurance and how they react. In this particular work, scientists have studied the molecular gas in space that is being strongly irradiated by ultraviolet rays. The team, led by Sara Cuadrado (ICMM-CSIC), has performed (the words in bold are explained below) a complete spectral survey of lines in the millimeter range using the IRAM30m telescope. This spectral survey (a kind of thorough review of that entire range of the electromagnetic spectrum) has been carried out at the edge of the photodissociation region of the Orion Bar, which is being irradiated by a very intense field of distant ultraviolet radiation.

But let us take it one step at a time.

Maybe you already know the Orion Bar from other previous reports: it is located within the well-known Orion Nebula, about 1,300 light years from Earth, and is the closest massive stars formation region.

The energetic far ultraviolet reaches this area of the Orion Bar. This ultraviolet range of light comes from young and massive stars that are forming  nearby (the stars known by the name of the Trapezium) and emit much of their energy in this range of the electromagnetic spectrum. The far ultraviolet is responsible, in this case, for the photodissociation of the molecules.

The photodissociation region is the one in which ultraviolet light is dissociating, that is, separating the atoms of the molecules (although, at the same time, new bonds between atoms may be forming, creating new molecules). The photodissociation region of the Orion Bar is very special because, being “close”, we can study it in detail.

The millimeter range is the range of the electromagnetic spectrum that allows us to study cold areas of the cosmos. For an astronomer a “cold” environment is one in which the temperature does not allow us to observe it because it emits poorly and it is very difficult to detect objects. Infrared and millimeter help us “see” those cold objects. 

Finally, the lines we are talking about are like fingerprints of chemical species. We detect them in space and they are reflected in lines like the ones I show you:

Image 2: Orion Bar Spectrum.

Well, despite the fact that the Orion Bar is a hostile environment where it was only expected to  find very simple molecules, the observations show spectra with many lines (the team has detected more than 850!), of which about 250 correspond to complex organic molecules and related precursors  [1]: methanol, formaldehyde,  formic acid  (the ants one), acetaldehyde, etc.

What does this mean?

La zona de la Barra de Orión sufre el castigo constante de la radiación ultravioleta emitida por estrellas masivas jóvenes del entorno. Por eso se pensaba que no podía haber complejidad química. Pero la hay. Y, aunque se desconocen los procesos por los cuales se forman estas especies descubiertas en el borde de la Barra, se han planteado varios escenarios que explicarían cómo se forman las moléculas orgánicas complejas halladas:

The Orion Bar area suffers the constant punishment of ultraviolet radiation emitted by young massive stars in the environment. That’s why it was thought that there could be no chemical complexity. But there is. And, although the processes by which these species discovered at the edge of the Bar are formed are unknown, several scenarios have been proposed that would explain the formation of the complex organic molecules found:

The first scenario would take into account new chemical reactions that only occur in the hottest gas and that have not yet been included in current theoretical chemistry models that try to reproduce the processes that occur in the interstellar medium.

In the second, complex organic molecules would be produced on the hot surfaces of the nearly bare grains (without ice sheets [2]).

And, in the third scenario, the dynamics of the photodissociation regions (something like currents of motion within the cloud) would cause complex organic molecules or their precursors, which have formed in the icy mantles of dust grains inside the molecular cloud, to sublimate and reach the edge of the Bar.

In short: the presence of complex organic molecules in the interstellar medium is more ubiquitous than initially expected. It includes environments as adverse as gas in the process of colliding at high speeds and, now, gas strongly illuminated by distant ultraviolet radiation. The formation of complex organic molecules reflects the complicated interaction between the chemical processes that occur in the gas phase and on the surface of the dust grains, leaving us with the question of what do all these molecules do in the Bar?

For Sara Cuadrado, “The formation routes of these species are not entirely clear and may not even be the same in different environments. More theoretical studies and laboratory experiments are needed to investigate the different chemical processes that take place on the surface of grains. The next step is, thanks to the new and increasingly powerful telescopes, to study regions similar to the Orion Bar to learn more about the different mechanisms taking place in these chemically surprising regions.”

Going back to the title of this report, you will understand that we sing the chorus of the “Ultraviolet” song from U2, “Baby, baby, baby, light (photodissociate, photoionize and photodesorb) my way”.


[1] H2CO, CH3OH, HCO, H2CCO, CH3CHO, H2CS, HCOOH, CH3CN, CH2NH, HNCO, H213 CO, and HC3N (in decreasing order of abundance). The inferred column densities are in the range 1011— 1013 cm-2. The work also provides the upper limit of abundance for some organic molecules that have not been detected in spectral scanning, but are present in other star formation regions: HDCO, CH3O, CH3NC, CH3CCH, CH3OCH3, HCOOCH3, CH3CH2OH, CH3CH2CN, and CH2CHCN.

[2] The desorption of complex organic molecules from the icy mantles that coat the dust grains by the action of UV radiation is one of the main mechanisms of formation of these species in the interstellar medium, a mechanism known as photodesorption. But this process does not occur on the illuminated and warmer edge of the Orion Bar, as the dust grains are no longer coated by ice.

More information:

This work has been published in the paper Complex organic molecules in strongly UV-irradiated gas”, by S. Cuadrado (Molecular Astrophysics Group, Institute of Materials Science of Madrid –CSIC, Spain); J. R. Goicoechea (Molecular Astrophysics Group, ICMM-CSIC, Spain); J. Cernicharo (Molecular Astrophysics Group, ICMM-CSIC, Spain); A. Fuente (Observatorio Astronómico Nacional – IGN, Spain); J. Pety (Institute of Millimeter Radio Astronomy (IRAM); LERMA, Paris Observatory, CNRS/PSL Research University, France); and B. Third (Molecular Astrophysics Group, ICMM-CSIC, Spain).


Image 1: Orion Nebula: The Orion Nebula, an immense stellar nursery about 1,500 light-years away. This stunning false-color view has been based on infrared data obtained with the Spitzer Space Telescope.  Credits: NASA/JPL-Caltech

Image 2: Orion Bar spectrum: Part of the spectral survey in the Orion Bar photodissociation region obtained with the IRAM-30m radio telescope. Credit: Sara Cuadrado.

Originally published in Spanish on the Naukas website: “¿Qué tiene el ultravioleta que a todas horas…? (2017/10/23).