More statements by IRC+10216: “You’re very heavy on carbon, really”

Summer has passed and, both CW Leonis and his companion envelope, IRC+10216, have come out of their media silence to make a statement to the hottest program of the moment (well, of the decade, just in case this takes longer). After her first statements, torn out in 2015, and a new complaint about the treatment given to her by the media in 2016, CW Leonis first told to the journalists of “The Life of the Stars” that, since ALMA (the daring paparazza who pursues her and her wrapping) does not give in to her efforts, she will be the one who tells the latest events herself. And, apparently, the thing is burning.

As in the most famous soaps, as in the most classic Variete programs, as in the most vitoreed gossip television programs (??), the life of this star and its envelope continues to hoard astronomical covers. It is the price to pay for a star that is close to us (who are very curious): that you become a model (to follow) of evolved (carbon)rich star.

And this is precisely the protagonist on this occasion: carbon.

In many astronomical environments it is common to find molecules formed by linear carbon chains (atoms go more or less “in a row”, but making a kind of zigzag, depending on the case). As always in astrochemistry, we are surprised to find long chains, as the conditions are so hostile that we assume that the bonds between atoms will be photodissociated as soon as an ultraviolet beam arrives. But the thing is, there they are.

Possible formation mechanisms involve upward and downward pathways, i.e., molecules can be formed by destroying larger molecules (carbon species such as C₆₀ or polycyclic aromatic hydrocarbons –PAHs-) or step by step, from smaller molecules.

Our protagonist, IRC+10216 (the envelope formed when the star CW Leonis begun to age and expand), has again been spied on by the set of ALMA antennas that, with the help of gossipy researchers, has combined these stolen photos with a computer simulation to discover how linear carbon chains are formed.

Thus, as Marcelino Agundez (ICMM-CSIC), leader of the gossipy researchers, mentions, “We have been able to witness the polymerization of acetylene and hydrogen cyanide induced by ultraviolet photons, that is, how the carbonated chains grow ‘step by step, we stick little by little…’ -sorry, it’s a famous Spanish song-, it is, very slowly. In addition, in this place, the carbonated chains are formed by a very concrete upward route. Oh, haven’t we said where yet? Because the most curious thing about this case is where we found these long chains. They really had that under wraps!

A hollow spherical shell

“I am really tired,” declares the envelope somewhat irritated. “I see on the covers of those gossip magazines that you have managed to capture several hydrocarbon radicals and other species [1]. And you have found them in an area of myself that you have called “hollow spherical shell”! This is the end… you don’t even let me have an inhomogeneity! Well, if you want a perfect envelope, do it with Photoshop! Stop it!

It turns out that all the species that ALMA has unveiled in this photo shoot are distributed in a hollow spherical shell [2]. It is as if, in the envelope itself, there was a bubble, someway isolated from the rest of the environment, that facilitates the growth of these molecules by protecting them from the conditions that occur outside it. This finding implies that the carbon chain formation mechanism in IRC+10216 is only activated in a very specific region of the external envelope [3].

In addition, it has been seen that the spherical shell itself has several thin layers (such is the capacity of ALMA’s “super-lens”) of an angular resolution of 1-2”, which are not strictly concentric. And here, dear readers, is where the third character reappears… the possible companion star!

CW Leonis, IRC+216… and the mysterious companion star

Why is the fact that the layers of the bubble are not concentric suspicious? The process of mass loss of CW Leonis (which is not the consequence of a diet, poor star, but of a process of aging towards white dwarf… although that will be another story) is discontinuous and not isotropic.

What does this mean? There is something, some kind of process related to a possible gravitational attraction, which is making the envelope not uniform, to have “deformations” that take place periodically and affect the distribution of its matter.

And what could be producing that effect? We’re pretty sure it’s a companion star. All we have to do is see it (here ALMA looks at us dismissingly, “I let this job to the HST or the JWST, this is not my busines. I’ve done enough already, before me you didn’t see the details so accurately.”

So we may face a very special threesome. CW Leonis does not want to comment on this. She merely talked about carbon chains by saying: “We know that, due to our proximity and luminosity, we are an ideal “laboratory” for studying the formation of carbon chains; we are aware that, for years, we have been persecuted by the paparazzi (there they have been IRAM30m, BIMA, IRAM Plateau de Bure, VLA and SMA). That won’t be necessary anymore. For a small price we will gladly tell you.”

This astounded us. Without a doubt, given the results of so much pressure exerted on our star, we only have to hope that some paparazzi will get in the future a deeper look to tell us more about the mechanisms that hide behind the formation of carbon chains. Or, what the hell: about the trio, which is what we’re really interested in. What will be the name of the mysterious companion star (if any)?

Notes:

[1] The λ 3 mm emission of rotational lines of hydrocarbon radicals C₂H, C₄H and C₆H and species containing CN, such as CN, C₃N, HC₃N and HC₅N with an angular resolution of ~ 1’’’ have been mapped. Hydrocarbon radicals C₂H, C₄H and C₆H show very similar radial distributions, while species containing CN show a more diverse radial stratification, with HC₃N presence in shorter radius and the CN radical extending outwards to larger radius.

[2] The spatial distribution of these species is a hollow spherical shell, with a width of 5-10”, located within a radius of 10-20” from the star, and no appreciable compact emission sample near the star.

[3] The observed morphology can be explained by a chemical model in which the growth of polyines is mainly caused by chemical reactions of radicals C₂H and C₄H with unsaturated hydrocarbons, while cyanopolyines are mainly formed from polyines by reactions with CN and C₃N radicals.

More information:

Paper: “The growth of carbon chains in IRC +10216 mapped with ALMA”, Astronomy & Astrophysics.

Image:

In red and green, dust detected by Herschel; in blue, the visible scattered light seen by the Very Large Telescope. The center light has been removed, so we don’t actually see the CW Leonis star, but rather her envelope. Credit: ESA/PACS/MESS & ESO/VLT

Originally published in Spanish on the Naukas website: Más declaraciones de IRC+10216: “Sois muy pesaos con el carbono, de verdad” (2017/09/07).

2017/04/172021/06/24

Calibrating the Submillimetre Sky

For astronomers, one of the most important things in order to be able to confirm and compare the huge amount of data received during the observations is to have accurate calibration references. In astronomy, millimetre and submillimetre wavelengths are important to study relatively cold objects in the Universe, such as the interstellar medium, star forming regions, circumstellar matter, planetary atmospheres and highly red-shifted objects. Reference calibration standards are, however, very scarce specially at submillimetre wavelengths (Bands 7, 8, 9 and 10 of the Atacama Large Millimetre Array, ALMA, in Northern Chile).

Fortunately, some years ago a team of astronomers suggested the use of the planets of our Solar System as possible calibration references at submillimetre wavelengths. First works developed on that subject revealed the submillimetre lines of Phosphine (PH₃) in the atmospheres of Jupiter and Saturn, although the overall shape of these extremely wide features could not be measured due to technical limitations.

Now, for the first time, a team has measured the emission of the giant planets Jupiter and Saturn across the 0.3 to 1.3 mm wavelength range using a Fourier Transform Spectrometer mounted on the 10.4-meter dish of the CSO, Caltech Submillimetre Observatory (now retired) at Mauna Kea, Hawaii, 4100 meters above sea level. The calibrated data allowed the team to verify the predictions of standard radiative transfer models for both planets in this spectral region, and to confirm the absolute radiometry in the case of Jupiter.

This careful calibration included the evaluation of the antenna performance over such a wide wavelength range and the removal of the Earth’s atmosphere effects, allowing the detection of broad absorption features on those planets’ atmospheres.

As mentioned by Juan Ramón Pardo (lead author of the study, ICMM-CSIC, Spain), “Besides their physical interest, the results are also important as both planets are calibration references in the current era of operating ground-based and space-borne submillimetre instruments”.

Jupiter and Saturn are gaseous giants much larger but less dense than the inner rocky planets of our Solar System. Their atmospheres are extremely thick. Very wide collision-broadened lines of Ammonia (NH₃) and Phosphine (PH₃) dominate the overall shape of their submillimetre spectrum. Most of the several thousand exoplanets discovered to date are gaseous giants thought to be similar to Jupiter and Saturn. Therefore, the now measured submillimetre spectrum of our giant neighbours could also help as a reference in future spectroscopic studies of other planetary systems.

More information:

This research was presented in a paper entitled “Ground-based measurements of the 1.3 to 0.3 mm spectrum of Jupiter and Saturn, and their detailed calibration” by Juan R. Pardo et al., to appear in the journal Icarus on July 1st 2017, but already available on-line: http://www.sciencedirect.com/science/article/pii/S0019103516303827

The team is composed of Juan R. Pardo (Molecular Astrophysics Group, ICMM, CSIC, Spain); Eugene Serabyn (NASA-Jet Propulsion Laboratory, California Institute of Technology, USA); Martina C. Wiedner (LERMA, Paris Observatory, PSL Research University, CNRS, Sorbonne Universités, UPMC, France); Raphäel Moreno (LESIA, Paris-Meudon Observatory, France); Glenn Orton (NASA-Jet Propulsion Laboratory, California Institute of Technology, USA).

Source of Jupiter Raw Image: technotifier.com

2017/03/072021/06/24

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

Using the IRAM 30 meter radio-telescope at the Pico Veleta (Spain), an international team of astronomers has obtained the most complete radio-observations of the Orion B star-forming region, famous for hosting the iconic Horsehead and Flame nebulae. Taking advantage of the fact that the cold molecular gas shines at radio wavelengths, the team revealed the hidden anatomy of Orion B. Through a careful dissection of the cloud into regions of different molecular composition, this work sheds new light on how the coldest and densest molecular clouds give birth to new stars.

Stars are born in cold and dense condensations that develop in the interior of interstellar clouds. The strong winds and ultraviolet radiation from newly born stars then erodes and disrupts the parental cloud.

Using the IRAM 30 meter radio-telescope in Pico Veleta (Spain), an international scientific program led by Jérôme Pety (IRAM & Observatoire de Paris, France), has achieved the most complete observation of the Orion B cloud in the radio domain. This region is a huge reservoir of interstellar matter (mostly gaseous molecules and dust grains), containing about 70,000 times the mass of the Sun.

Emeric Bron and Javier Goicoechea, both from ICMM-CSIC (Spain) and members of the team, explain: “We have been studying the famous Horsehead nebula for years. The new instrumentation at the IRAM 30m telescope now allows mapping much larger areas of the sky and detecting the emission produced by different molecules simultaneously. The obtained maps are equivalent to about 160,000 images of 325×435 pixels, enough to make a movie of 1h50m at 24 frames per second. We have created images of the emission produced by molecules such as carbon monoxide, carbon monosulfide, cyanides, methanol, and small hydrocarbons. Detecting these molecules is crucial, since molecular hydrogen, which makes up about 75% of interstellar gas, is invisible in cold molecular clouds. Detecting the radio emission from those species is thus not only important to understand the chemistry of these regions, but it also provides the best radiography of cold molecular clouds that are otherwise invisible to the naked eye (see Fig. 1).”

This project provides unprecedented images of a region of the sky that is only seen as a dark region in the visible. Moreover, the wealth of data opens the possibility to characterize the structure and the physical and chemical properties of molecular clouds in unprecedented detail. It is truly a dive into the inner anatomy of the Orion B cloud. “Diffuse gas, filaments, and dense condensations could be the equivalent of muscles, bones, and vital organs, respectively. And the images of different molecular lines enable to radiography different parts of Giant Molecular Clouds, just like Magnetic Resonance Imaging (MRI) enables to reveal the interior of the human body” says Pety.

In the series of 3 articles accepted by Astronomy & Astrophysics, the team explains how the emission from different molecules is a very sensitive diagnostic tool of the gas physical conditions, its density, temperature, turbulence and the properties of the ultraviolet light arising from massive stars in the region. The team shows how the sites for future star-formation, the coldest and densest condensations, are only revealed by the emission from certain molecules such as the diazenylium ion (N₂H⁺).

Another important result is the discovery of a clear relationship between the kind of turbulent motions (shocks or vortices) and the local star formation activity. This pioneering work, involving the simultaneous statistical analysis of many molecular tracers will provide the needed tools to characterize star formation in the interstellar medium. It brings radio-astronomy into the era of big data!

Star Wars inspiration

Astronomy is very inspiring and also very cinematographic. Our perception is determined by our experiences. This is why it is not surprising that, while observing the sky, we are able to find wonderful shapes and even characters (the origin of constellations names).

This is what happened to Audrey Pety, pursuing design studies, who says: “I immediately saw the skeleton of a Jedi knight when first discovering this image. This reminded me that constellations are human interpretation of the stellar patterns on the sky and that Orion is a hunter. And I ended up drawing my own modern constellation on this image (Fig. 2).”

Contacts

Emeric Bron – Emeric.Bron@csic.es
Javier R. Goicoechea – jr.goicoechea@icmm.csic.es
Jerome Pety – pety@iram.fr

Images

Figure 1: Orion B molecular seen in the optical (lower panel: Image credit & copyright Sergi Verdugo Martínez) and as a composition of three radio emission lines observed in this work (¹²CO, ¹³CO and C¹⁸O isotopologues, upper panel). The ionized hydrogen gas shines in bright red in the optical, whereas radio observations reveal the intrinsic structure of the dense molecular gas (Image credit & copyright J. Pety, the ORION-B Collaboration & IRAM).

Figure 2: Artistic view of a Jedi knight overlaid on an image of the molecular gas from Orion B (Image Credit & Copyright: Audrey Pety).

Additional information

Project history

The ORION-B project results from 10 years of research. It was made possible by the advent of a new generation of wide bandwidth receivers combined with high resolution spectrometers at the IRAM 30 meter telescope, and builds on long experience in radio-astronomy by the team members. Jérôme Pety explains: “Using the IRAM 30 meter telescope, we undertook in 2011 a systematic survey of the chemical content of the Horsehead’s mane, during a project named Horsehead WHISPER. This allowed us to discover in 2012 a new molecule in the interstellar medium, the propynylidyne ion (C₃H⁺) that is a member of the hydrocarbon family. Building on this success, we decided to generalize these observations, i.e., to observe one hundred thousand positions in Orion B instead of a single one towards the Horsehead nebula, each direction delivering information at 160,000 different frequencies!” Harvey Liszt, astronomer at NRAO, adds: “It’s flabbergasting to see how this field has grown tremendously. During my PhD, I tuned a precursor millimeter receiver to obtain the first noisy detection of carbon monoxide towards one direction in Orion B, together with Nobel prize winner Bob Wilson. And only 45 years later, we easily gets such wide maps for so many molecules over the whole cloud!” No doubt that the future will offer even faster and wider observations for radio-astronomers. When that happens, the pioneering statistical approach of the ORION-B project will provide the needed tools and experience to handle bigger and bigger datasets.

Scientific papers

“The anatomy of the Orion B Giant Molecular Cloud: A local template for studies of nearby galaxies”, by Jérôme Pety, Viviana V. Guzmán, Jan H. Orkisz, Harvey S. Liszt, Maryvonne Gerin, Emeric Bron, Sébastien Bardeau, Javier R. Goicoechea, Pierre Gratier, Franck Le Petit, François Levrier, Karin I. Oberg, Evelyne Roueff, Albrecht Sievers.
“Dissecting the molecular structure of the Orion B cloud: Insight from Principal Component Analysis”, by Pierre Gratier, Emeric Bron, Maryvonne Gerin, Jérôme Pety, Viviana V. Guzman, Jan Orkisz, Sébastien Bardeau, Javier R. Goicoechea, Franck Le Petit, Harvey Liszt, Karin Öberg, Nicolas Peretto, Evelyne Roueff, Albrecht Sievers, Pascal Tremblin.
“Turbulence and star formation efficiency in molecular clouds: solenoidal versus compressive motions in Orion B”, by Jan H. Orkisz, Jérôme Pety, Maryvonne Gerin, Emeric Bron, Viviana V. Guzmán, Sébastien Bardeau, Javier R. Goicoechea, Pierre Gratier, Franck Le Petit, François Levrier, Harvey Liszt, Karin Öberg, Nicolas Peretto, Evelyne Roueff, Albrecht Sievers, Pascal Tremblin.

Links

STAR WARS and all related characters, names are registrated trademarks or copyrights of Lucasfilm Ltd., or their respective trademark and copyright holders.

2017/02/132021/06/25

IK Tau, an “oxygenated” death

The death of stars is the main phenomenon responsible for the enrichment of the interstellar medium, both in terms of the number of elements and in terms of their chemical complexity, and one of the objectives of astrochemistry is to understand how chemical processes that we know on Earth take place in space.

The difference in environmental conditions, however, could make us think that it is impossible for some events that do take place on our planet to happen in space. Nothing further from the truth: despite being hostile environments (in most cases) in the universe there are processes of chemical complexity that are often unexpected.

This is the case of IK Tau, an evolved solar-type star that is in one of the last stages of its life, the AGB or Asymptotic Giant Branch phase. At this stage, the star inflates, increasing its size hundreds of times, and creates an envelope that will gradually release its material into the middle.

For the first time, an international research team, led by Luis Velilla, from the Institute of Materials Science of Madrid (CSIC), has made an extensive survey of the envelope of this oxygen-rich AGB star.

And why is this study interesting? Normally, evolved stars are either rich in oxygen or rich in carbon, and the latter have always been considered more complex and chemically active. Let’s say stars with oxygen-rich envelopes were considered more “boring”, chemically speaking. In fact, the models on which the studies of these two types of evolved stars are based take these factors into account, confirming a more active character in carbon-rich envelopes.

But, given the results of this work, perhaps the approach that has prevailed so far will have to be changed. We will have to start looking at the “oxygenated” stars with different eyes.

Unexpected results

After several observation campaigns carried out between 2009 and 2013 with the IRAM-30m telescope, located in Sierra Nevada (Granada, Spain), the data have revealed the presence of approximately 350 spectral lines emitted by numerous species carrying elements such as H-, O-, C-, N-, S-, Si- and P (approximately 20 molecular species). In addition, for the first time in this source, lines of HCO^+,NS, NO, and H₂CO, as well as several isotopologues of previously identified molecules have been detected [1].

Several lines of high excitation of SO₂ have also been detected, which is interesting, since the models do not predict that, under the conditions of temperature and density of the inner region of the envelope, SO₂ can form so abundantly.

This would prove that oxygen-rich molecular envelopes have a much more complex chemical activity than previously believed.

A reservoir of data

One of the important aspects of this work, apart from the discoveries of molecular species not expected in these environments, is the large amount of data it provides to continue studying this type of object, since it has detected numerous lines of molecules previously identified in IK Tau, allowing a detailed study of molecular abundances and excitation temperatures. That is, if before there were simple detections, now there is enough data to make larger and deeper studies.

On the other hand, this work will not only serve as a reference for the studies of the chemical evolution of solar-type stars (in particular, of stars 4,000 million years older than our Sun), but also makes it necessary to rethink the current chemical models when reproducing the formation of species in the inner regions of oxygen-rich AGB stars.

Studying these envelopes helps us understand how the elements react to form, first, simple molecules composed of two atoms (such as NS) and, later, molecules such as formaldehyde (H₂CO), keys to the subsequent formation of complex organic molecules.

As always when we talk about astrochemistry, our search is associated with the great unknown that we have not yet managed to clear: the chemical origin of life.

NOTE:

[1] C¹⁸O, Si¹⁷O, Si¹⁸O, ²⁹SiS, ³⁰SiS, Si³⁴S, H¹³CN, ¹³CS, C³⁴S, H₂³⁴S, ³⁴SO, y ³⁴SO₂.

Image:

IK Tau is an evolved star surrounded by an envelope composed of dust and gas. This envelope blocks most of the visible light emitted by the star. In this false color image, from the Sloan Digital Sky Survey, we see the object in an intense red color.

More information

This work has been published in the paper “The millimeter IRAM-30m line survey toward IK Tau“, and its authors are Luis Velilla Prieto (Instituto de Ciencia de Materiales de Madrid, ICMM-CSIC; Centro de Astrobiología, CAB/INTA-CSIC, Spain); Carmen Sánchez Contreras (CAB/INTA-CSIC, Spain); José Cernicharo (ICMM-CSIC, CSIC, Spain); Marcelino Agúndez (ICMM-CSIC, Spain); Guillermo Quintana-Lacaci (ICMM-CSIC, Spain); Valentín Bujarrabal (National Astronomical Observatory, OAN-IGN, Spain); Javier Alcolea (OAN-IGN, Spain); C. Balança (LERMA, Paris Observatory, Sorbonne University, France); F. Herpin (University of Bordeaux, LAB; CNRS, LAB, France); K.M. Menten (Max-Planck Institute for Radio Astronomy, Germany); and F. Wyrowski (Max-Planck Institute for Radio Astronomy, Germany).

Originally published in Spanish on the CulturaCientífica website: “IK Tau, una muerte oxigenada” (2017/02/13).

2016/09/302021/06/25

The Bug Nebula* and the (no) One Ring

How many times in astronomy (and, in general, in the world of science) did we discover something that wasn’t the goal that moved us in the beginning? These “collateral” discoveries are sometimes more relevant than originally sought. Other times, they complement certain fields of study with their contributions.

Miguel Santander (researcher at the Molecular Astrophysics Group of the Institute of Materials Science of Madrid (CSIC)) knows something about this, as he sometimes finds, along with his team, surprises that have led him to publish his results in the journal Nature (you can see one of these stories in his Talk of Naukas “How to be a Star, Die Twice and Do It in Style”). [1]

However, on this occasion, this is not about stars, but about rings.

To start where it’s right, we need to explain what a planetary nebula is. Well, a planetary nebula is the corpse of a low-mass or intermediate star (usually stars that have up to eight solar masses). They draw our attention because it is difficult to explain how a spherical object (we assume that stars are essentially spherical) can give rise, when dying, to such diverse and fantastic forms.

The star, by depleting the hydrogen from its nucleus, goes through several phases that will cause it to swell, multiply its size hundreds of times, and end up releasing its matter into the medium, leaving its remains in the center in the form of a dense white dwarf star. Around it, the gas that was once part of it desegregates, partially condensing into dust grains and forming different molecules. Its final destiny will be the total disappearance of the planetary nebula as we see it now. It will eventually fade into the interstellar environment and, most likely, the life cycle of the stars will begin again when gas and dust gather elsewhere and condense enough to generate nuclear reactions. But that’s another story. Let’s get on with the planetary nebula.

A while ago, the result of the work of a team (led by Valentín Bujarrabal of the OAN-IGN) that studied the presence of material discs around evolved stars was unveiled. These are discs very similar to those created when the stars are born, although we do not know many of their characteristics and we also do not know if planets could be born in these discs of dying stars. With the intention of further researching these interesting discs, observation time was obtained with the ALMA interferometer, a radio telescope formed by 66 antennas and located in the Atacama Desert in Chile.

And when they received the data, there was a surprise.

A nebula not only asymmetrical

We’re still asking the question. How is it possible for spherical objects such as stars to give rise to such different symmetries and, in some cases, so extreme? This is what happens to our protagonist, the Bug Nebula (NGC 6302), a relatively young planetary nebula whose central star has a very high temperature (it is not really yet known if there are one or more stars in the center, but that is the subject of another study).

The shape is impressive (see image 2). A fiery center from which stellar winds come out, caused by the white dwarf, that ionize the whole medium and shape bipolar jets, also known as lobes (those that make the nebula appear to be a bug with wings or have the shape of a diabolo). But, wait a moment… We don’t see the center.

And we don’t see it in this image because there’s a dust and gas ring that prevents it. First, let’s make a clear distinction between ring and disc. We were looking for a much smaller type of disk than this ring and we haven’t detected it. But there’s that ring and, if you look at it, in the visible range of light we see an arc-shaped filament wrapped in the main lobes. Although we do not know very well what it is… unless we observe in other light ranges, such as millimeter and submillimeter, the ranges in which ALMA observes and which manage to provide us with surprising information.

The One Ring?

Some nebulae have, around the nucleus, a very dense and thick gas and dust ring that is usually associated with its extreme symmetry and that we believe is related to the star’s winds, the presence of a companion or magnetic fields.

In the case of the Bug Nebula, the ring creation process began about 5,000 years ago and lasted approximately 2,000 years. Later, in a space of time that would go between 3,600 and 4,700 years ago, the lobes were created. But the planetary nebula does not have a single axis of symmetry or a single bipolar jet. About 2,200 years ago, another jet emerged from the nucleus, this one with a different symmetry. That is, there is a third lobe, younger and with a different axis than the main lobes.

But that’s not all.

In parallel, at a similar time, another structure was formed whose existence was not known until now: a second ring, younger than the first, that is oriented in another direction (see image 3) and which also expands faster.

Although it is not the first planetary nebula discovered with several rings with different degrees of inclination, it is the first time that it is estimated that there is quite a difference in age and mass between the rings. The secondary rings of other planetary nebulae are almost as massive as the primary ones and, in this case, if the primary ring has 0.1 solar masses, the secondary ring has only 2.8 Jupiter masses.

Whom are you from?

Both the origin and orientation of this second ring of the Bug Nebula are a mystery to researchers, but there are several theories that speculate on its possible formation. One of them sets the stage for a triple system in which one of the stars would have gone through the red giant phase, destabilizing the entire system. The other two stars could have originated the new ring.

There’s another hypothesis that’s much riskier, but equally interesting. May the ring be the result of the destruction of a gas giant planet that would have been in an orbit too close to the star during its process of evolution to red giant.

In both cases it is speculation and reaching some plausible conclusion would require more accurate data from the particular area.

The case is that no, the discs originally sought and for which observation time was requested have not been found, but a new type of ring has been discovered casually. Science gives us surprises.

Notes:

[1] This talk is inspired by the results of this scientific paper: “The double-degenerate, super-Chandrasekhar nucleus of the planetary nebula Henize 2–428”.

Paper: ALMA high spatial resolution observations of the dense molecular region of NGC 6302

Links:

Press Release (in Spanish): Descubierto un segundo anillo en la Nebulosa del Insecto

Images:

Image 1. Planetary nebulae. Credit: Montage by Judy Schmidt.

Image 2. Bug Nebula. Credit: NASA, ESA and the Hubble SM4 ERO team.

Image 3. Rings of the dense molecular region of the Bug Nebula seen by ALMA. Credit: M. Santander-García et al./ALMA/HST

Video:

ALMA observations in ¹²CO and ¹³CO (carbon monoxide isotopologues) overlapped on a background image of the Hubble Space Telescope. The number shown at the bottom corresponds to the velocity relative to the Local Standard of Rest (LSR) in km/s (the systemic velocity -the center of mass of the system is -30.4 km/s). The emission traces the structure and speed pattern of both rings. The left (west) region of the inner ring is associated with the arc-shaped filament visible in the Hubble image. Credit: M. Santander-García et al./ALMA/HST

Originally published in Spanish on the CulturaCientífica website: “La nebulosa del Bicho* y el anillo no único” (2016/09/30).

2016/06/032021/06/25

The dust trap

It is becoming increasingly clear that there are planets in the least expected places: floating alone in space (ejected from their systems), around stars like ours (which was the most logical thing to do), around pulsars (the first exoplanets discovered), and around stars smaller than our Sun. We did not see them and now the numbers are getting out of hand, although the ones that interest us the most are the Earth-like ones, of rocky type. But what conditions exist in those debris disks where planets are born to be of one kind or another?

Protoplanetary disk around the star AB Aurigae.

The birth of the planets is the end of a process that involves a lot of condensation and concentration of matter. In the beginning, we have a faint molecular cloud in space, with grains of dust and gas molecules floating randomly. At some point, the matter begins to condense at certain points that, if the necessary conditions are met, will eventually collapse and create stars. The star will have around it the remains of his own formation, the debris, which will end up forming a disk around him.

That excess matter, composed of gas and dust, will be “floating” around the star, generating, over time, discs of material in which these debris are “condensed” and end up forming planets (we have also talked about second generation disks, something intriguing that is still being studied). So, we can say that the stars are the “mothers” of the planets.

Knowing the composition of these disks, their physics and their chemistry, is fundamental to know what a planet needs to form. That is to say: depending on the raw material we have and the conditions that occur, we will have planets or not and, if we have them, they will be rocky or gaseous.

As it could not be otherwise, we are intrigued to know how the Earth was formed, what conditions were given for the emergence of a planet like ours. To try to know more, we studied the disks of young stars, similar to our Sun in its early stages, in order to try to establish certain parallelisms. One such star is AB Aurigae, a Herbig Ae-type star that hosts a well-known protoplanetary disk in which the planet formation phase appears to have started, a stage known as the “transition disk,” a step between that stage of material accumulated in the disk and planetary formation.

Inside the disk, one of the key places when it comes to studying where and how the planetary birth begins is the so-called “dust trap”, the place where we see that there is greater accumulation of dust within a disk of debris.

NOEMA images of the transition disk of AB Aurigae.

A trap from which you will not be able to escape… or maybe yes.

The “dust trap” is so named because the data indicate that the dust grains are trapped for a very long time, which would facilitate the formation of the seeds of the planets [1]. Another interesting aspect is the shape of the disk which, in this case, is slightly altered, which could be an indication that planetary formation has begun: interferometry data indicate that it is horseshoe-shaped [2].

At first, protoplanetary disks have an abundant amount of gas that will be lost over time, as planets form and the disk is “cleaned” of debris. Some of that gas will also be integrated into the planet. In fact, in this work, led by Susana Pacheco-Vázquez and Asunción Fuente, of the National Astronomical Observatory (OAN-IGN), the chemical composition of the gas of the disk of the star AB Auriga has been studied and several simple organic molecules [3] and sulfur monoxide (SO) have been detected.

Sulfur is one of the most abundant elements of the Solar System. However, so far this is the only protoplanetary disk in which SO has been observed. But that’s not the only mystery: the expected amount of SO isn’t found in the dust trap. Almost all molecules have a horseshoe-shaped spatial distribution, just like dust. However, the spatial distribution of the SO looks more like a ring with uniform emission. This would only be understood if the SO were less abundant in the dust trap than in the rest of the disk.

One possible explanation for understanding where the SO that we did not find could go would be that these SO and SO₂ molecules, given the high-density conditions that occur in the dust trap [4], were frozen on the surfaces of the dust grains. And, with observations in the millimeter range (the range in which the coldest objects emit) the molecules in the ice cannot be detected, so we did not find the expected amount of SO.

What does it mean whether or not there is SO in a dust trap? In principle, its presence, absence or even abundance could be used to know if the disk we are studying is approaching the phase in which it begins to create planets. And, since the gas and dust found in protoplanetary disks are the raw material from which planets are born, understanding their chemistry can shed some light on the eternal question: the origin of life.

Notes

[1] The maximum dust emission corresponds to a maximum gas pressure at which the dust particles would be trapped for a long time, about 0.1 Myr (million years).

[2] The transition disk is highly skewed in azimuth, presenting a morphology disproportionate with the maximum to the southwest.

[3] The compounds detected are HCO+, H₂CO, HCN, CN, CS and SO.

[4] The team has come to this conclusion after performing detailed calculations on chemistry, excitation and radiative transfer that simulate the physical conditions in the protoplanetary disk and study the chemistry of sulfur within the dust trap.

Comparison between the spectra modeled and those detected by the 30-meter telescope towards the AB Aurigae disk. The blue and magenta lines correspond to the same model with disk tilt angles of 27◦ and 40◦ respectively.

Images

Image 1: Protoplanetary disk surrounding the Star AB Aurigae. Credits: Hubble Space Telescope/C.A. Grady (NOAO, NASA/GSFC), et al., NASA.

Image 2: NOEMA images of the transition disk of the star AB Aurigae.

Images with high spatial resolution (~1.6”= 231 AU) of the lines of C¹⁸O 2->1, H₂CO 3_0.3->2_0.2 and SO 5₆ -> 4₅ obtained with NOEMA. The emission of the molecular lines follows the ring detected in the continuous dust emission (at 1mm). The dust trap is clearly detected in the 1mm continuum and in the C¹⁸O image. However, the SO line has an almost uniform emission along the ring with no significant enhancement.

Radiative transfer, chemical and excitation calculations have been performed, simulating the physical conditions of a protoplanetary disk, in order to investigate the chemistry of sulfur in the region of planet formation. Our model shows that the high-density conditions characteristic of the dust trap would lead to a rapid freezing of the SO and SO₂ molecules on the grain surfaces. The absence of some volatile molecules such as SO can therefore be used as a chemical diagnosis to detect the existence of an environment in which planets are being born.

Image 3: Comparison between the spectra modeled and those detected by the 30-meter telescope towards the AB Aurigae disk. The blue and magenta lines correspond to the same model with disk tilt angles of 27◦ and 40◦ respectively.

More information:

This work has been published in the paper “High spatial resolution imaging of SO and H2CO in AB Auriga: the first SO image in a transitional disk”, published in the journal “Astronomy and Astrophysics”, and its authors are Susana Pacheco-Vázquez (OAN-IGN), Asunción Fuente (OAN-IGN), Clément Baruteau (CNRS, IRAP), Olivier Berné (CNRS, IRAP), Marcelino Agúndez (ICMM), Roberto Neri (IRAM), Javier R. Goicoechea (ICMM), José Cernicharo (ICMM) and Rafael Bachiller (OAN).

This work has been carried out with observations of the NOEMA interferometer and the IRAM 30m radio telescope. The observations with the IRAM 30m radio telescope were carried out within the large ASAI program (IRAM chemical survey of sun-like star-forming regions), whose principal investigators are R. Bachiller and B. LeFloch. NOEMA’s observations were made by an international team led by the National Astronomical Observatory (IGN).

Originally published in Spanish on the Naukas website: “La trampa de polvo” (2016/06/03).

2016/05/102021/06/24

Flatulence in Space (III)

It’s sad to beg, but sadder is to beg over and over again, until exhausting our audience… It’s my case, I admit. It’s my fault. In my quest to increase the number of followers of the ASTROMOL’s Facebook account (wink-wink), I embarked on a smelly adventure in which I promised articles about stinky gases if I overcame every challenge. The first, “Flatulence in Space (I)”,was published in August 2015. January 2016 saw the birth (or, rather, smelled the birth) of “Flatulence in Space (II)” and, since there are no two without three, we tried again. The last one was hard, but we’ve made it. And since I do what I promise, here’s the third (and who knows if the last one, snif) deliver of “Space Flatulences”. Don’t cry for me 😉

“Nature never ceases to amaze us.” As if it were the script of a documentary, I see myself pronouncing this phrase as I choose the title of this report. I know it’s a little scatological, but it’s totally true: let’s talk about some of the gases that are in our flatulence. Watch out, in our flatulence there’s not just gas, there are more things, but we’re not going to talk about those. The compounds that give farts that smell (not all smell the same, it will all depend on what we have ingested) are well known. And some of them are also in space. Now you’ll understand why I, who usually talk about Astrophysics and Astrochemistry, get into these issues.

Hydrogen sulfide and carbonyl sulfide are the two pestilent compounds we have already talked about in this series. But today we do not bring sulfide, today we bring methyl mercaptan or methanethiol (CH₃SH), a second cousin of methanol (CH₃OH), which replaces sulfur (S) with oxygen (O). This mercaptan, from the thiol family, is a colorless gas that smells of rotten cabbage (although, in truth, I’ve never smelled a rotten cabbage, anyone with experience? Comments, please).

It appears to be in numerous plant and animal tissues and occurs in some processes of bacterial breakdown of proteins from methionine (as Wikipedia faithfully tells us), that is, a zombie would stink of CH₃SH. It’s in the poop and farts (and in the stinky breaths) but, pay attention, it’s also in our brains (I see the joke coming) and in the blood.

There are also some cheeses that contain it and smell like this, to methyl mercaptan (you have an example in the Beaufort’s cheese) because of the action of some unleashed microorganism. Swamps emanate this smelly compound, but exposure would only be dangerous if we talk about industrial issues (and yet the danger of methyl mercaptan is not demonstrated). It is used as a precursor to pesticides, in the manufacture of plastics and feed, to break down wood in paper factories and is added to jet aircraft fuels.

Methanethiol is one of the gases added to the butane (remember that butane smells nothing) so that we get the olfactory alarms in case of leakage. (That reminds me of an olfactory fire alarm designed for deaf people who let out a wasabi spray. This research won an Ig Nobel Prize in 2011).

What about space?

Methyl mercaptan was detected in 1979 by Linke and collaborators in Sagittarius B2, a molecular cloud of the galactic center known to be one of the most productive massive star formation areas in the galaxy. So, we could already say that it had been detected in the interstellar medium.

Subsequent studies also detected the presence of methyl mercaptan towards the hot core of G327.3-0.6, a region of massive stars formation (this was the first time that methanethiol was found outside the galactic center).

It was also detected in the cold molecular cloud B1 (this cloud is located in the so-called First Hydrostatic Core stage, formed when the collapse phase at the star’s birth stage is stopped. We had already spoken before about this detection).

And, very recently, methyl mercaptan has been found in the protostar IRAS 16293-2422. Its finding suggests that there may be entire families of Sulphur-carrying molecules that have not yet been detected in protostars and would form from CH₃SH.

It has been searched in other environments but, so far, has not yet been detected. Although there are proposals to use it as a biomarker when researching the surface of Mars. As a result of a biological process (you know, farts and so on) this, and other compounds of its kind, can help find signs of life on Mars or in the atmospheres of exoplanets. The linked work above explains that methanethiol may be involved in the origin of life in places with hydrothermal activity at low temperatures caused by serpentinization (a process that consumes water and releases heat). This process could take place on Mars, in icy oceans of moons or satellites, and in other smaller bodies, as well as on Earth.

Thus, detecting the presence of methyl mercaptan could be a tool for detecting signs of life. Although, honestly, we return to the usual: detecting a particular compound that we associate with the presence of life does not necessarily imply that there is life. There are many processes, in addition to farts, that can lead to the formation of methyl mercaptan. In this series of “flatulence in space” we always get to the same point: the origin of life.

And this because, dear friends, it seems that life, although it can be wonderful, sometimes stinks. 😉

Image:

Image 1: Space-filling model of the methanethiol molecule. Credits: Ben Mills.

Links:

List of molecules detected in space on the astrochymist web.

The methyl mercaptan on the “astrochymist” website.

Information on the toxicity of methyl mercaptan on the “Agency for Toxic Substances and Disease Registry” website of the Centers for Disease Control and Prevention (Atlanta, USA). Public Health Summary.

Originally published in Spanish on the Naukas website: “Flatulencias espaciales (III)” (2016/05/10).

2016/05/092021/06/24

The torus around a supermassive black hole, observed for the first time

Using the ALMA (Atacama Large Millimeter-Submillimeter Array) array, a team of researchers, led by Santiago García-Burillo (of the National Astronomical Observatory (OAN-IGN), Spain) has managed to observe, for the first time, the dust and gas torus surrounding a supermassive black hole, in this case the one at the center of galaxy NGC 1068 (also known as Messier 77).

Active Galactic Nuclei (AGN) galaxies are those that harbor a supermassive black hole at their core with signs of recent activity. These types of black holes accrete material while emitting a large amount of energy over a wide spectrum of wavelengths. It is believed that all galaxies, at some point in their lives, can be active galaxies.

For a period of activity to be triggered, the central supermassive black hole must be “fed” and, for a long time, it has been postulated that the fuel should be stored on a dust and gas disc surrounding the black hole. Although the immediate environment of the black holes of active galaxies may be as bright as the entire galaxy that houses it, some of these nuclei appear to be hidden behind a ring-shaped structure of dust and gas, called a “torus”.

The torus (or doughnut) shape, adopted in many theoretical models, would explain many of the enigmatic and spectacular features observed in active galaxies. But, due to the great distance that separates us from these objects, to isolate that small structure we need advanced instrumentation and the use of interferometric techniques, capable of achieving a very high angular resolution [1]. This has finally been made possible by the ALMA (Atacama Large Millimeter/submillimeter Array) antenna array.

This is the first time that a circumnuclear disc of this type -its composition, dust emission, gas distribution and even its movement- is clearly observed [2].

NGC 1068 or Messier 77

This galaxy is one of the most active and, at the same time, one of the closest to us (it is about 50 million light years away), so, for decades, it has been the subject of numerous observational studies that have tried to detect the presence of that disc of torus-shaped material at its center, surrounding the supermassive black hole.

For Santiago García-Burillo, astrophysicist at the National Astronomical Observatory (OAN-IGN), member of ASTROMOL and principal investigator of this work, “These observations are an evidence of what ALMA can do, managing to spatially detect and solve very small structures in nearby galaxies. We will be able to know more about the behavior of these discs and how they stabilize around the supermassive black holes, feeding them to create monsters whose mass can reach from millions to billions of times the mass of our Sun.”

These observations demonstrate the existence of these discs. However, the torus discovered in NGC1068 appears to be much more complex than expected. The next step will be to study other similar galaxies to see if this uncovered complexity is a common phenomenon in galaxies with active nuclei or whether, on the contrary, NGC 1068 is an exception.

Notes:

[1] Better than 0.1″ (arcseconds).

2] The emission in the continuum of dust from the torus has been obtained, but, most notably, the torus has also been spatially resolved in the emission of molecular gas. To do this, the 6-5 rotational line of carbon monoxide (CO) was used as a dense gas tracer (n(H₂)~1×10⁵ cm^-3). This allowed to derive the size of the torus (about 7-10 pc ~ 26 light-years in diameter) and study the kinematics of the gas, which turns out to be very complex: the gas would be expected to rotate regularly at these distances around the black hole, however, in addition to the gas disc appears to be praised, the gas has strong non-circular movements superimposed on rotation.

More information:

Paper: ALMA resolves the torus of NGC 1068: continuum and molecular line emission.

Other links:

– NewScientist: Dusty doughnut around massive black hole spied for first time (Shannon Hall).

Images:

Image 1: The NASA/ESA Hubble Space Telescope has captured this vivid image of spiral galaxy Messier 77 — a galaxy in the constellation of Cetus, some 45 million light-years away from us. The streaks of red and blue in the image highlight pockets of star formation along the pinwheeling arms, with dark dust lanes stretching across the galaxy’s starry centre. The galaxy belongs to a class of galaxies known as Seyfert galaxies, which have highly ionised gas surrounding an intensely active centre. Credit: NASA/JPL-Caltech. Link to the original image.

Image 2: Emission on the continuum of the dust captured by ALMA on the circumnuclear disc of NGC1068 from scales of ~200 parsec ~ 600 light-years (panel-a) to the scales of the torus ~7-10 parsecs ~ 26 light-years (panels b and c).

Image 3: Emission (a) and speed field (b) of molecular gas detected by ALMA on the circumnuclear disc of NGC1068.

2016/04/262021/06/24

Second generation planets?

Planets are born around young stars in formation. They arise from the rotating discs of remains of material, which are left over after the birth of the star itself. Then, the surroundings of the star, already with their planets emerging, are “cleaned” of diffuse material and stay relatively clear. Until a few years ago we thought that discs were exclusive to those early stellar stages, but then it was discovered that no, that stars in advanced phases again had discs of material around them. And that’s where the question arises: could there be second-generation planets?

When sun-like stars run out the fuel of their nuclei, they start a decline consisting of various stages. One of them is the red giant phase, in which it swells considerably and begins to expel its material in the form of layers, as in a slow wave of gas molecules and dust grains. This is where stellar winds push that material out. The star continues to “get rid” of its layers, reaching the highest mass loss phase, the Asymptotic Giant Branch, or AGB.

Many stars that have already crossed this stage (called post-AGB) in binary systems (pairs of stars orbiting each other) have a disk made up of gas and dust that revolves around both stars. We know that they exist, but we ignore the details of their formation, structure and evolution, although surprising similarities have been found with discs that revolve around young stars. [1]

There is research that considers the possibility that these gravitationally linked dust discs exist in many binary stars in advanced stages. In fact, the data is even used the other way around: the presence of a disk indicates that it can be a binary system with a post-AGB star.

The Red Rectangle

In 2003, a team led by Valentín Bujarrabal, a researcher at the National Astronomical Observatory (OAN-IGN), discovered that the planetary nebula known as the Red Rectangle had a rotating disc [2]. This nebula, studied with the IRAM interferometer, also launches jets of material at low speed and has a complex structure in which there is a binary star system whose main star is a post-AGB.

Until early 2015, only this rotating disc had been clearly studied and identified. The second disc of this detected type was the one orbiting around other evolved star: AC Herculis. From this moment on, scientists suspected that these discs play a key role in late stellar evolution and were abundant around evolved stars.

Bujarrabal, principal investigator of both works, states that these, and other published results, are part of a long collaboration maintained by the OAN team with the Institute of Astronomy of Leuven: “We were the first to demonstrate the existence of discs rotating around old stars, as normally the material around them, which has been ejected by them, is expanding. Some of our latest observations, particularly using ALMA and VLTI, are really spectacular and contain a huge amount of information about these amazing objects.“

The data that ALMA is providing will be decisive in the future to compare this type of disc with those around young stars. At the moment, thanks to the VLTI interferometer, the most accurate image of a disc around an evolved star, IRAS 08544-4431, formed by a red giant and a less evolved one, has been obtained.

The image is impressive: the dust ring surrounding the stars is clearly visible. From all these observations it has been inferred that the discs surrounding old stars are very similar to the discs around the young stars. And if they’re so similar, could planets form?

Wait a minute, let’s rewind.

Born and die

We are at the moment just before the stars are born (our protagonists are always mid-sized stars). The molecular cloud, laden with gas and dust, is compacted at some points where matter ends up condensing and ignition begins in the stellar nuclei. Around them, these young stars have discs on which planets can eventually form. Once formed, there may even be a “dance” of planets, called planetary migration, that causes some to change orbit around their star until the system stabilizes.

The stars normally live their hydrogen consumption stage in the nucleus, until it is finished and drift begins. The red giant phase is so overwhelming (because of its huge size and impressive increase in luminosity) that the planets will most likely end up slashed, pushed or broken. It will all depend on the distance that separates the planet from its star and, again, the planetary migrations between orbits.

Of course, planets could overcome that phase and still exist (very battered, yes). And this has led to quite a few confusions when it came to determining whether a star (as in BP Piscium’s case) was young or old – the same thing happened with Gomez’s Hamburguer, which was believed to be an old star until it was studied in depth and was seen to be a young star that probably has a protoplanet orbiting around it.

But would a second generation of planets be possible? What specific conditions should be given? Could the remains of first-generation planets, along with the materials of the second disc, form new planets? How long would it take to do so? Could the energy of the dying white dwarf left in the center feed that system?

As for the possible existence of second generation planets, there are already studies related to the first exoplanets detected, discovered in 1992, which also revolved around a pulsar: PSR B1257+12. But in this case, we are not talking about the death of sun-like stars (between one and eight solar masses) but a hypothesis about something that could have happened after the death as a supernova of a much more massive star [3].

Moreover, in the environments of evolved mid-mass stars, in the final stages of their lives, so far, no planets have been found in formation. Scientists theorize about which environment would be most appropriate, which parameters they should meet, but nothing has yet been detected that can confirm these hypotheses.

Meanwhile, researchers like Bujarrabal continue to study these second-generation discs to determine how they form and what their final destination is.

Notes

[1] For example, in its mineralogical composition, as is the case of the AC Her binary system, which contains a post-AGB star, and the protoplanetary disk of the young star HD100546.

[2] Valentin Bujarrabal himself published a beautiful report entitled “The Colloquium of the Nebulae”, inspired by Cervantes’ “The Colloquium of Dogs”, in which the Rectangle Nebula and the Pumpkin Nebula have a dialectical encounter. You can find it in the yearbook of the National Astronomical Observatory (OAN-IGN) of 2014 and in this link (in Spanish).

[3] Some argue that a millisecond pulsar could explode in the form of a Quark-type nova. This still hypothetical object, the result of a previous explosion of supernova, would generate a disk capable of forming planets. This theory could explain the existence of the planets around the PSR B1257+12 pulsar.

Image:

Image 1: Rectangle nebula. Credit: ESA, Hubble, NASA. Link to the image, APOD (Astronomy Picture of the Day), June 14th, 2010.

Originally published in Spanish on the Naukas website: “¿Planetas de segunda generación?” (2016/04/26).

2016/03/082021/06/24

“Gas on the rocks”: shaken, not stirred

Methyl isocyanate in space and in comets

One of the translation errors (from English to Spanish) that has caught my attention the most has been that of the expression “on the rocks”. I’ll never forget that Hollywood classic where someone asks another character for a whiskey and says, “Yes, on the rock” (literally, put the glass on the stone rock!) … In Spanish the translation should have been, “Yes, only with ice.” Equally curious is the translation of “Shaken, not stirred” for the Martini, which brings translators crazy, although it seems this expression has been the most used by James Bond. The erroneous expression in Spanish “Sí, sobre la roca” is very useful to talk about not whisky, but gas: the gas that is deposited on the “rock” (whether a grain of dust or a comet) and which, later, may end up being transformed into ice. All very “on the rocks” and very mixed.

Today, detecting new molecular species in space is something relatively normal. It is very complex, because molecules emit in the range of the least energetic electromagnetic spectrum, and that is why very sensitive instruments are necessary. To date, a large number of molecular species have been detected, and about 30% of these detections have been carried out by Spanish research teams.

One of the goals in all astrochemical research is to understand how chemical phenomena take place in space: is it important that a molecule found in a comet is also present in the interstellar environment? How can the mixture of molecular species condition the emergence of life or the future characteristics of a planet? What amounts are needed? Is there any relationship between the chemistry of the primitive Solar System and the current one?

Dense interstellar clouds are the places where stars and planets form. Most of its mass is essentially molecular gas with a small fraction of tiny grains of dust [1].

On the other hand, dust grains usually have a nucleus of silicates on which the molecules of the gas phase are adhering and accumulating, forming ice sheets on the grain. This occurs during the gravitational collapse of the clouds of gas and dust, clouds from which new stars and planetary systems like ours will form, resulting in giant gaseous planets and rocky bodies such as Earth, asteroids and comets.

Our Solar System was formed 4.5 billion years ago from an interstellar cloud of gas and dust and, therefore, the composition of the bodies that emerged from it is closely linked to the composition of the interstellar cloud from which they were born. Thus, it is considered that, for example, the icy surface of comets is a repository of information that tells us about the composition of the gas and dust that was in the primitive solar nebula.

Comet 67P/Churyumov-Gerasimenko and the Orion Cloud

The recent analysis of the composition of the icy surface of comet 67P/Churyumov-Gerasimenko [2] by its lander, Philae, revealed the existence of a significant number of complex organic molecules, most of them already detected in gas phase in interstellar clouds.

But among the species detected on the surface of the comet there was one that had not previously been observed in interstellar clouds: methyl isocyanate (CH₃NCO).

Philae detected the molecule with a mass spectrograph, but to detect a molecular species on a comet, techniques other than those used in the interstellar medium are used. In fact, to confirm its presence in the interstellar medium, a thorough analysis had to be performed consisting of obtaining the rotational spectrum of molecules in a molecular spectroscopy laboratory, so that frequencies and lines corresponding to that molecule could be obtained.

After hard laboratory work that began in 2010, an international research team, led by José Cernicharo (from the Molecular Astrophysics Group of the Madrid Institute of Materials Science (ICMM) of the Higher Council for Scientific Research (CSIC)), discovered, in the clouds of Orion, methyl isocyanate. In fact, from this observation work, carried out with the data obtained with the IRAM 30-meter radio telescope and the ALMA interferometer, 400 lines of this molecule have been characterized and detected.

This result, together with previous analyses of other comets studied from the ground, has led to the development of important work in the search for a possible connection between interstellar and cometarian molecular abundances.

CH₃NCO

Methyl isocyanate (CH₃NCO) could play an important prebiotic role in the formation of peptides that could be important in the chemical evolution of primitive Earth. It is known that, at room temperature, methyl isocyanate reacts with water and with many substances containing N-H or O-H groups [3], common in the gas phase in Orion.

Although it is a potentially relevant molecule in the chemistry of the interstellar medium, it had so far not been included in any chemical model and has not been released until now in astrophysical journals. However, as Cernicharo states, “We intuit its presence by similarity to other previously detected species and finally confirm it. To our surprise, it is one of the most abundant molecules with a methyl group and an isocyanate group.”

Orion’s massive star formation region is the prototype of “hotcore”, the most promising areas to search for CH₃NCO. Its most active part is the Kleinmann-Low nebula (Orion-KL) where a group of newborn stars, deeply embedded in the region, interacts with their surrounding material: the fact that it has been detected in hot nuclei and not in dark and cold clouds suggests a chemistry dominated mainly by the activity in the mantle of dust grains. That is, the evaporation of the ice sheets of the dust grains produces a very rich chemistry (when the original gas molecules mix with the ones that arise from that evaporation).

On the other hand, we assume that the frozen surface of comets maintains memory of the composition of the dust grains of the primitive solar nebula. These dust grains, if similar to Orion’s, will expel molecules as soon as they are heated by radiation or impacts with cosmic rays.

It will be of great interest to observe the comet’s coma to learn about the abundances of gas phase species and to obtain information on how molecules that survived the ejection of the comet’s surface have been identified. In addition, laboratory experiments on ice are essential to learn about CH₃NCO formation processes on these surfaces. Knowing its original composition will help us to know more about what are the conditions necessary for systems similar to ours to emerge, systems that start being simply “gas on the rocks”.

Laboratory characterization

In 2006, this research team initiated an in-depth survey of lines in Orion KL’s millimeter domain (80-280 GHz) with the IRAM 30m radio telescope with the aim of fully characterizing its chemical composition. However, due to the high kinetic temperature ofthe gas [4], there were many rotational and vibrational levels of abundant species that produced a forest of spectral lines (i.e., there was a huge amount of information “overlapping”, difficult to decipher).

The number of unidentified lines was too large to perform a realistic search for new molecular species. Initially, about 15,000 spectral lines were detected, of which 8,000 were unknown. It was necessary to initiate systematic work in spectroscopic laboratories to characterize all the isotopologues and vibrationally excited states of the most abundant species in Orion-KL in order to identify unknown lines.

Numerous isotopologues and vibrational states were characterized in the laboratory, later identifying them in the data and reducing the number of unidentified lines to 4,000, some of them particularly strong [5].

Of the expected 523 lines of CH₃NCO in the data obtained by the team, 282 are not mixed with others and 119 are partially mixed with other species (without this preventing them from being identified on the line profile). The other 122 lines are completely mixed with lines of other more abundant species, most of them in the 1.3 mm (197-280 GHz) wavelength domain, where the density of lines in Orion grows enormously.

Notes:

[1] The fraction of dust grains is ~1/200. The most abundant molecular species is molecular hydrogen (H₂), followed by CO. More than 180 complex molecules are added to this list in different proportions.

[2] The COSAC (Cometary Sampling and Composition) experiment, aboard the Rosetta mission’s Philae lander, has measured in situ the abundances of the main surface components of comet 67P/Churyumov-Gerasimenko.

[3] CH₃NCO was responsible for the deaths in the Bhopal industrial disaster.

[4] T_K~ 100-300 K

[5] A large number of isotopologues containing ¹³C, ¹⁵N, ¹⁸O and vibrationally excited states of species such as CH₂CHCN, CH₃OCOH, CH₃CH₂CN, and NH₂CHO among others, were fully characterized in the laboratory and identified in the data. New molecules such as ammonium, NH₃D⁺, methyl acetate, CH₃COOCH₃ and CH₃OCH₂CH₃, methyl ethyl ether, were also detected.

More information:

Paper: “A rigorous detection of interstellar CH3NCO: An important missing species in astrochemical networks”, Astronomy and Astrophysics Journal.

Images:

Orion Nebula in the infrarred. This wide-field view of the Orion Nebula (Messier 42), lying about 1350 light-years from Earth, was taken with the VISTA infrared survey telescope at ESO’s Paranal Observatory in Chile. The new telescope’s huge field of view allows the whole nebula and its surroundings to be imaged in a single picture and its infrared vision also means that it can peer deep into the normally hidden dusty regions and reveal the curious antics of the very active young stars buried there. This image was created from images taken through Z, J and Ks filters in the near-infrared part of the spectrum. The exposure times were ten minutes per filter. The image covers a region of sky about one degree by 1.5 degrees. Credits: ESO/J. Emerson/VISTA. Grading: Cambridge Astronomical Survey Unit.

Video:

Artistic impression that takes us on a 3D journey through the Orion Nebula. Credit: ESO/M. Kornmesser. Original video link: https://www.eso.org/public/spain/videos/eso1006e/

Originally published in Spanish on the Naukas website: “Gas on the rocks: mezclado, no agitado”(2016/03/08).