Category: Outreach

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IRC+10216 returns: “Leave me alone!”

Following the angry statements made last summer in a well-known star celebrity program asking for respect for their intimacy, the IRC+10216 circumstellar envelope and her partner, CW Leonis, offer new exclusive statements.

Large-scale structure of the IRC+10216 circumstellar envelope

“I love CW Leonis, not because she’s rich -in carbon-.  We are in a moment of maturity and we want to enjoy the years that remain,” confesses the IRC+10216 envelope, very close to its starmate.

From her side, the evolved star states: “I know that we are special, but that is no reason for ALMA to continue to be a pin in the neck. What does it matter if we have a peculiar distribution of CH3CN?”

For those who are not aware this hot topic (quite literally), we should remember that IRC+10216 and CW Leonis maintain a very close relationship. Last July they were caught in fraganti by the powerful paparazzi (or, rather, paparazza) of the stars, ALMA [1].

In those “stolen” photos, ALMA allowed a group of researchers (very snoopers) to determine the distribution of SiS, SiO and SiC2 in IRC+10216.

She didn’t stop there, and she now reveals that, at the time, she also discovered something unexpected: the peculiar distribution of CH3CN (known as acetonitrile).

Acetonitrile.

What we thought we knew

Until now, the chemical structure of carbon-rich evolved star envelopes was thought to be well known. It was described mainly by the action given in two scenarios: one, located in the warm and dense surroundings of the star, in which we find a chemical balance that allows the formation of stable molecules, and another, located in the outer layers of the envelope, in which, due to the penetration of ultraviolet photons, radicals and more exotic species are formed. 

However, these last few years have been disconcerting, as aspects that do not fit in these scenarios have been discovered [2].

The latest “photos” made public by ALMA indicate that CH3CN is not formed far, but in the inner regions of the envelope with much greater abundances than predicted by chemical balance [3].

Most of the emission is distributed as a hollow shell located just 2 arcseconds from the star (which, over astronomical distances, and for the case at hand, is very little). What catches the eye is that this spatial distribution is much more different from those found to date in this source for other molecules.

In fact, the standard chemical models of IRC + 10216 predict that most CH3CN molecules should be present at a distance of 15 arcseconds from the star.

Is it possible that phenomena related to dust grain condensation or the action of interstellar ultraviolet photons (capable of passing through our lumpy envelope) are reaching chemical equilibrium zones? Or maybe it is related to the non-uniform structure of IRC+10216, as it has gaps, arches and areas where matter accumulates that could explain this mystery.

IRC+10216 and CW Leonis say they don’t know anything about acetonitrile. “Let it get distributed as it pleases, of course. And if I catch ALMA again sticking her nose in our private lives, we’re going to get into hot water. We have left the matter in the hands of our lawyers.”

For Marcelino Agúndez, one of the “snoopers” researchers who has worked on this topic, from the Molecular Astrophysics Group of the Institute of Materials Science of Madrid (CSIC), “IRC+10216 does not know where she is getting into. Why CH3CN and no other molecular species? She will have to give a lot of explanations. And not because we’re interested in her private life, that’s not what it’s about. They’re hiding something and sooner or later everything will come to light.”

We said it last summer: maybe there’s a companion star orbiting CW Leonis. As this ends up being true, the scenes in “Save Me from Star” will give enough material to create a Youtube channel.

Notes

[1] The use of millimeter and submillimeter interferometers such as ALMA, able to investigate the distribution of different molecules in the inner regions of the circumstellar envelopes, is a very promising tool to reveal the role of the processes outside the thermodynamic balance that take place in these inner regions. These results come from data obtained in ALMA Cycle 0, with observations in band 6 of rotational transition J = 14-13 of CH3CN in IRC+10216.

[2] The most prominent examples are the detection of hot water vapour in IRC+10216 and other carbon-rich envelopes, as well as the observation of HCN in oxygen-rich envelopes, NH3 in carbon and oxygen-rich envelopes, and PH3 in IRC + 10216.

[3] Maximum s abundance of ~ 0.02 molecules per cm-3 to 2 arcseconds of the star are reached.

More information

Paper: “The peculiar distribution of CH3CN in IRC+10216 seen by ALMA” (DOI: 10.1088/0004-637X/814/2/143), Astrophysical Journal (ApJ)

Images

Image 1: Large-scale structure of the IRC+10216 circumstellar envelope, seen through the brightness of the carbon monoxide (CO) J=2-1 line. Observations have been made with the radio telescope IRAM 30m (Granada) and are described in this article (Cernicharo et al 2015, A&A, 575, A91).

Image 2: Spacefill model of acetonitrile. Credits: Benjah-bmm27, wikipedia.

Video:

IRC+10216 time-lapse: http://www.physics.usyd.edu.au/~gekko/irc10216.html

“The animation to the left cycles back and forth over about 3 years of time-lapse images. The motion of the clumps and plumes of dust, which are glowing hot here in the inner regions near the star, can be seen as a sort of “breathing” in the movie. As the dust flows out from the star, it eventually disperses into the galaxy, finding its way into big clouds which may, in due time, collapse again to form a new generation of stars (see the young star images). What is crucial, however, is that this new generation of stars will be formed from material with a different chemical composition, because the outflows from stars like IRC +10216 contain elements heavier than hydrogen and helium, elements like carbon, nitrogen, iron, silicon. Indeed if it weren’t for these dying stars enriching the chemistry of the matter in the galaxy, there would be no rocky planets, no metals, and no life. Most of the matter which forms every human body, if you go back a few billion years, must have been part of the shroud of a dying star just like this one”.

Credits: Peter Tuthill, Australian Research Council, US National Science Foundation Stellar Astronomy and Astrophysics Program.

Originally published in Spanish on the Naukas website: Vuelve IRC+10216: “¡Que me dejéis en paz!” (2016/02/15).

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Who’s so tEMErarious in the fierce Orion?

Looking for trans ethyl methyl ether in Orion KL

When the Big Bad Wolf threatened the Three Little Pigs with blowing and blowing until destroying their houses, they challenged him by saying that each would build his house of a different material: straw, wood and brick. Obviously, it doesn’t take long to build a thatched or wooden house as a brick house (so the story criticized the vagrancy of two of the piglets). The wolf managed to blow down the houses of straw and wood (imagine the lung power of the canis lupus), but not the brick one, where the three tEMErarious piglets ended up scalding the fierce wolf. (My inner child wondered if that brick house, made so hastily, was not going to be a terrible quality one…).

The key factor, in this case, was time.

In Astrochemistry we also handle that variable (as in the entire universe) to determine the chemistry of gas in the interstellar medium. How long does it take for changes to be made to the chemistry of a given environment? What conditions of temperature, pressure, or other parameters, are needed?

In this particular work, we talk about the tentative detection [1] of a molecular species: by identifying a large number of lines of rotation of the molecule, a team of researchers, led by Belén Tercero (ICMM-CSIC), has presented in this paper the tentative detection, in Orion KL, of trans ethyl methyl ether (t-CH3CH2OCH3, from now on, tEME). In addition, in order to try to restrict the type of chemical processes that occur in this source, they also carried out the search for gauche-trans-n-propanol (Gt-n-CH3CH2CH2OH, an isomer of tEME, which we will call, for short, Gt-n-propanol).

But we’ve put a lot of technicality in at once… what does all this mean?  Let’s go in parts.

First, what are rotation lines?

Molecules have different energy levels: electronic, vibrational and rotational. Because the energy is quantized, we can know what kind of transition has taken place when a molecular species is excited or deexcited (i.e. when its energy levels rise or drop).

Within a particular electronic state, the molecule can reach different types of vibrational states (those produced by the vibration of the atoms that make up the molecule) and, in turn, within the same vibrational state, the molecules rotate in space around their bonds.

These rotation changes can be detected with radio telescopes in the millimetric and submillimetric wave domain (the less energetic range of the electromagnetic spectrum), resulting in spectra loaded with lines to “translate”.

Thanks to the analysis of the data provided by the IRAM 30m radio telescope and the ALMA interferometer, lines of both species (tEME and Gt-n-propanol) have been identified, even being able to obtain maps with their spatial distribution [2].

Thousands of lines

A few years ago an exhaustive study of the Orion KL region was carried out with the IRAM 30m radio telescope. The result showed more than 15,400 spectral lines of which some 11,000 were identified and attributed to 50 molecules (199 isotopologues and different vibrational modes). To date, there have been several jobs based on this data.

As a result of fruitful collaboration between astrophysicists and laboratory molecular spectroscopy experts, 3,000 previously unidentified lines were assigned. Three molecular species and 16 isotopologues and vibrationally excited states of molecules abundant in Orion, never before detected in space, were identified.

With the same data set, now, a research team, led by Belén Tercero (ICMM-CSIC), has published the detection of another new molecule in space, tEME. In addition, several unidentified lines in this data have been provisionally identified as belonging to Gt-n-propanol (a tEME isomer).

Spatial Distribution

Our protagonist molecular species (which, more than a wolf, looks like a poodle).

With ALMA data, maps of the spatial distribution of oxygen-carrying saturated organic species containing methyl, ethyl and propyl groups have been carried out, estimating the abundance ratios of related species and the upper limits of column densities of undetected ethers [3].

As for its provenance, while the tEME comes mainly from the “Compact ridge” area of Orion, the Gt-n-propanol appears in a hot core of southern Orion. Until now it was thought that the “Compact ridge” area was the main host of all oxygen-carrying organic saturated species in Orion, but recent studies (including the one at hand) show other regions within Orion KL where these complex oxygen-rich molecules are significantly more abundant than in “Compact ridge”. This result suggests a chemical complexity not yet well characterized, related to the processes that create and segregate these species in the region.

The abundance and spatial distribution of these molecules suggest important processes that would take place in the gas phase that occurs after the evaporation of the mantle that would cover the dust grains in the warmest areas of the region.

To summarize, by combining IRAM 30m and ALMA data, we can provide a solid starting point for the definitive identification of tEME in the interstellar medium.

Fierce Wolf

The formation of complex molecules in space is a mystery to unravel. Although, for starters, we should differentiate the term “complex molecule” on Earth and in space. Of course, given the hostile conditions in the interstellar environment and in environments such as Orion KL, combining molecules and forming more complex species is an achievement. Hence species that on earth can be common, in space are called “complex”.

Gradually we discover that dust grains, protective “bubbles” created by pressure, temperature and jets of material, and other phenomena that take place in space, generate environments that promote these changes.

As fierce as Orion KL is, there seem to be places where these chemical combinations make their way and, as much as it “blows”, they will continue to stand, tEMErarious, facing the hostilities, combining and surprising us over time.

Notes:

[1] In Astrochemistry we usually talk about tentative detection when we have almost all the keys to confirm the presence of a molecule in a certain environment but we lack a piece of the puzzle (in some cases, more than one). In this case, we talk about tentative detection because certain species that have a very abundant and complex pattern of rotational lines must be identified over a very wide range of frequencies to ensure detection. This work shows that in the frequency range studied there is no missing piece of the puzzle.

[2] Maps of CH3OCOH, CH3CH2OCOH, CH3OCH3, CH3OH, and CH3CH2OH are also provided to compare the distribution of these oxygen-carrying saturated organic species containing methyl and ethyl groups in this region. The work also includes abundance quotients of related species and higher limits to the abundances of undetected ethers.  An abundance ratio of N(CH3OCH3)/N(tEME) ≥to 150 is derived in Orion’s “Compact ridge”.

[3] Column density is the amount of material contained in an imaginary cylinder (usually with a cross-section area of 1 cm2) between an observer and an astronomical object. (Oxford-Complutense Astronomy Dictionary, Ian Ridpath, 1999, Editorial Complutense). The derived column densities for these species at the location of their emission peaks are ≤(4.0±0.8)×1015 cm−2 and ≤(1.0±0.2)×1015 cm−2 for  tEME and Gt-n-propanol, respectively. The rotational temperature is ∼100 K for both molecules.

Link to the paper: Searching for Trans Ethyl Methyl Ether in Orion KL

Image: «Methoxyethane-3D-balls», by Ben Mills and Jynto – Derived from File:Ethanol-alternative-3D-balls.png. Available under public domain license via Wikimedia Commons.

Originally published in Spanish on the Naukas website: ¿Quién tEME al Orión feroz? (2016/01/25).

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Flatulence in Space (II)

A few months ago, from Astromol’s facebook, we posed a challenge: if we could reach four hundred followers, we would write more reports on stinky gases in the universe. And we got over them. In fact, since the publication of “Flatulence in Space (I)“, we have exceeded eight hundred. So here’s the second part of “spatial flatulence,” dedicated, this time, to carbonyl sulfide.

“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.

After talking about hydrogen sulfide (H2S) in “Flatulences in Space (I)“, today we will focus on carbonyl sulfide (OCS) which, although having a very nice name, does not fall short in terms of danger compared to the previous compound.

On our planet, carbonyl sulfide, a colorless gas, is produced in swamps, inside volcanoes, in the oceans, in hydrothermal sources and, pay attention, in fertilized soils (manure) and other environments. It is present in some grains and seeds, and in some cheeses and prepared cabbage.

Humans release carbonyl sulfide to the environment after certain processes (no, we don’t yet talk about farts), for example, combustion, when we use the car, in coal-fired power plants, when processing fish (all this is said by Wikipedia and I believe it), in the manufacture of some products, but in all these cases they are a result, an impurity generated after a process (what is called a by-product).

It is known that inhaling it in high concentrations for a short time can cause narcotic effects in humans and can irritate eyes and skin. But if we stay too long, it can cause seizures and lead to collapse and death from respiratory paralysis. This happens because, as with hydrogen sulfide, it affects our nervous system, nullifying our olfactory capabilities and leaving us exposed to danger. So you know, if you detect something smelly, walk away just in case.

Another danger is its combustion capacity: it is a highly flammable gas [1]. And according to this company in Canada, under pressure it’s corrosive.

Finally, as you already knew, this sulfur compound is found in flatulence, albeit in a very low proportion. In fact, its presence in the environment is generally quite low, although it stinks of rotten eggs.

Apparently, this that smells so bad can be related to… (we know we repeat this a lot in astrochemistry and astrobiology, but it is simply the truth) the origin of life!

Carbonyl Sulfide in Space

It was 1971 [2] when Jefferts and his team detected the presence of OCS in the interstellar medium, specifically Sagittarius B2 (Sgr B2), one of the largest molecular clouds in our galaxy (its total mass is three million times the mass of the Sun and its size about 150 light years). Again, as with hydrogen sulfide, Penzias and Wilson, Nobel laureates thanks to their discovery of the cosmic microwave background, signed the article describing this finding along with P.M Solomon, astronomer at Columbia and California universities (remember that Jefferts, Penzias and Wilson worked for Bell Telephone Laboratories). [2]

In 1995 Mauersberger et al. reported on the first detection of carbonyl sulfide in an extragalactic source: the Silver Coin Galaxy or NGC253, a very bright galaxy that is nearly 13 million light-years from us.

The same year, the OCS molecule was also detected in ice mantles covering interstellar dust grains, near the W33A protostar.

Paradoxically, it took time to confirm its presence in our Solar System. In 1997 L.M. Woodney led the team that found this molecule on Comet Hyakutake. (As you may recall, in “Spatial Flatulences I”, we also talked about comets and the importance of detecting these compounds in these objects.)

But today we are going to focus on the detection of OCS in the atmosphere of the planet Venus, carried out in 1990. Studies suggest that, due to the difficulty of carbonyl sulfide to be produced inorganically, and since, on Earth, the presence of this gas is considered an indicator of biological activity, it would be interesting to review the atmospheric chemistry of the planet. But what happens, does anyone suggest there’s life on Venus?

Not exactly, but apparently in Venus’ atmosphere, about 50 km from the surface, lies the only place (after Earth) of the Solar System with an atmospheric pressure of almost one bar, temperatures that would allow the existence of liquid water (0 to 100 °C ), energy provided by the Sun and life-critical elements such as carbon , oxygen, nitrogen and hydrogen.

So far, missions launched to Venus have not detected microbial life. What has been done has been to confirm the distribution of OCS in the Venusian atmosphere thanks to ESA’s Venus Express mission and VIRTIS instrument, aboard the satellite. The data confirmed in 2008 that there is more carbonyl sulfide in equatorial regions than in high latitudes.

So, if we go to Venus, we should be prepared to smell what will surely not be a dish of taste because there smells like flatulence too. Although no, it’s not our last word.  

To be continued…

Notes

[1] Air flammability limits (under standard temperature and pressure conditions): 12.0-28.5 vol%

[2] Ten years later, in 1981, there were already ten interstellar and circumstellar sources in which the presence of SCO had been detected.

Image:

Space-filling 3D model of carbonyl sulfide. Ball-and-stick model of the carbon disulfide molecule, OCS. C=S bond length of 1.5601 Å; C=O bond length of 1.1578 Å. Data from CRC Handbook of Chemistry and Physics, 88th edition. Credits: Ben Mills. Wikipedia.

Links:

Data about OCS ant its discovery in different environments in www.astrochymist.org.

New Jersey Department of Health: hazardous substance fact sheet for Carbonyl Sulfide https://nj.gov/health/eoh/rtkweb/documents/fs/0349.pdf

Originally published in Spanish on the Naukas website:  Flatulencias espaciales (II) (2016/01/13).

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Orion’s skin

Orion is the nearest and brightest massive stars forming region, a “stellar nursery” that has become our astrophysical experimentation laboratory. It is so close that we can take images of the entire region and, at the same time, study details of it. In this article we will focus on how ultraviolet radiation from stars influences the interstellar clouds of gas and dust that surround them.

The Orion Nebula.

Interstellar clouds are areas of space “among the stars” formed by gas and dust, regions monstrously larger than the clouds of the sky in which, in some lumps “chosen” by gravity, matter can condense and collapse into stars. In particular, the great cloud of Orion is a tremendously active region of the sky. Within it stands out the Trapezium Cluster, a group of massive and very energetic stars surrounded by gases that can be seen from the ground even with small amateur optical telescopes.

Compared to our Sun, massive stars (more than eight solar masses) are huge and have shorter lives because they consume the “fuel” of their core very quickly. They are so energetic that powerful winds emanate from them that “shake” the whole environment, and also emit a lot of “sterilizing” light, especially in the ultraviolet (UV) range of the electromagnetic spectrum.

Massive stars grow so fast that there is no time for the cloud of molecular gas and dust that spawns them to disappear (as with the birth of lower-mass stars like our Sun), so that they destroy (photoevaporate and/or photoerode) the cloud that gave birth to them: they are like children who devour their parents.

For researchers it is very important to determine the impact these massive stars have on the progenitor clouds and also their impact on the whole galaxy, since their birth and existence determine the properties and future of the entire interstellar environment.

The Orion Nebula (annotated).

The main characters

To talk about this research we need to present the main characters, and the first is the aforementioned area of Trapezium, dominated by relatively young and massive stars (up to 30 times the mass of the Sun for the brightest star of Trapezium) and located on the sword of the “hunter” of the Orion’s constellation. The entire region is surrounded by the Orion Nebula, formed by a very hot gas that has been ionized by UV radiation emitted by these stars.

On the other hand we have the molecular cloud that lies just behind the Trapezium and the nebula. In this cloud of molecular gas and dust hundreds of protostars are being “incubated”, colder objects that are not yet “adult” stars but are in the process of formation (you can watch this video to have an idea of the distribution of matter in this area). While we need optical telescopes to capture visible light emitted by hot gas from the nebula, the only way to “cross” the region and see the molecular cloud is to observe it in infrared and radio waves.

And in the outer skin of that molecular cloud, very interesting things are happening. For example, we know that UV photons emitted by Trapezium stars are beginning to “burn” the cloud – starting with the skin – with mechanisms that researchers know well (e.g. ionization of atoms). This causes a bright flash of Orion’s skin in the range of the far infrared. Something like an interstellar “tan”.

We know our third character thanks to the data obtained with the HIFI instrument aboard the Herschel Space Telescope: we have been able to see the “skin of Orion burned” because it emits in the line of ionized carbon (C+), a line that traces how the molecular cloud is being photoevaporated.

Image of the [CII] 158μm emission captured by Herschel.

This C+ emission line, the brightest of the interstellar medium (we’ll call it the “superline”), is a fundamental tool for plotting how UV radiation destroys molecular clouds. It also gives us clues about the rate of stellar formation, a critical parameter in astrophysics to know fundamental details about our universe (how many stars are formed and at what rate?).

In addition, this emission cools interstellar neutral gas: the thermal agitation of the gas becomes, mainly, radiation emitted in the C+ line that escapes from the cloud and cools the medium. Emission is difficult to observe from the ground, so it is necessary to use space satellites or telescopes embarked on stratospheric aircraft to study it. In fact, the team that carried out this research work obtained ten hours of observation with the Herschel Space Telescope, managing to extract from the data and the maps information about the kinematics of the gas in the skin of Orion, thus revealing its three-dimensional structure and then elaborating this impressive video.

Far beyond time and space

The information we extract from this work doesn’t end here. We have a superline that tells us about how clouds are photoevaporated and how many stars are born in a certain environment of stellar formation, such as the Orion region. But what if it was able to tell us about much further areas?

By the redshift effect, which causes light emitted in a range to move to ever longer wavelengths (due to the expansion of the universe), the C+ line emitted from very far galaxies (when the universe was much younger) comes to us in the range of millimeter and submillimeter radio telescopes that astrophysicists build at high altitudes (as is the case with ALMA -Atacama Large Millimeter/submillimeter Array – installed in Chile’s Atacama desert, more than 5,000 meters high).

That means that, if we used to need ten hours with a satellite to observe regions of the Milky Way like Orion, now, in a matter of minutes, with radio telescopes like ALMA, composed of dozens of antennae, we can get the same information from very distant objects (young galaxies) thanks to that redshift of light.

But not only can ALMA offer great advances in detailed study of what happens in the “skin of Orion”. Members of the NANOCOSMOS team [1] participate in a project that has obtained time from the Impact Legacy Program to map the entire Orion region into C+ using the “upGREAT” instrument aboard SOFIA (Stratospheric Observatory for Infrared Astronomy). A NASA telescope “flying” at a height of about 14 km (about 4 km above commercial flights, fasten your seat belts!).

These are 54 hours of flights and observations (usually the programmes granted with SOFIA are one hour or less) that will be carried out over the next two years in order to map a region 20 times the one presented in this study. Astronomers, climbed on an airplane, will work from the stratosphere to learn more about Orion’s (less mysterious) skin in order to understand the mechanisms that produce the emission of C+ and then be able to understand more accurately the emission that ALMA observes from the primitive universe.

Study what we have around to understand what we observe far away. All thanks to Orion’s skin.

Notes

[1] The scientific team that obtained time with SOFIA is led by A. Tielens (Leiden) and includes three members of the NANOCOSMOS project (J. Goicoechea, O. Berné and J. Cernicharo). This project will allow the use of the C+ line to be established as a stellar formation rate indicator, to measure the mass of molecular clouds that cannot be measured with CO (the so-called “CO-dark” gas), and to determine semi-empirically the efficiency of photoelectric heating in PAHs (polycyclic aromatic hydrocarbons) and interstellar powder grains.

Images:

Image 1: The Orion Nebula.  The Orion Nebula seen by Hubble. Credits: NASA, ESA, M. Robberto (STScI/ESA) et al. (Link to image).

Image 2: The Orion Nebula (with annotations). Color composite image of the Orion Nebula (M42) taken in visible light with the Hubble Space Telescope (Robberto et al., 2013). The molecular cloud of Orion, where new protostars develop, lies behind the ionized nebula. Black contours show the emission of C+ in the far infrared detected with Herschel-HIFI, tracing the illuminated skin of the cloud (Goicoechea et al., 2015).

Image 3: Image of the [CII] 158μm emission captured by Herschel, with annotations indicating the location of the best known regions of the Orion cloud. Credits: Goicoechea et al., 2015.

Videos:

Video 1: This video shows ionized carbon emission at different gas speeds. Thanks to the “high spectral resolution” technique, gas movements can be distinguished in detail. This video is analogous to an Orion “scanner” in which, first, the peripheral regions of the Orion Nebula (especially atomic and ionized gas seen in images of visible light) are detected and finishes penetrating into the molecular cloud and dust hidden behind the visible nebula (with gas speeds above 8 km/s). The skin of the cloud (illuminated by UV radiation from the stars of Trapezium) can be seen in the gas that moves at speeds between 8 and 10 km/s. Credits: Goicoechea et al., 2015.

Vídeo 2: Spectacular 3D video of the Hubble Space Telescope inside the Orion Nebula. These stars are in a dramatic landscape of gas and dust reminiscent of the Grand Canyon. The Orion Nebula is an illustrated book about the massive formation of young stars. Credits: NASA, ESA, G. Bacon and the Science Visualization Team (STScI) https://hubblesite.org/contents/media/videos/2006/01/513-Video.html?news=true

Original video and more information: http://hubblesite.org/newscenter/archive/releases/2006/01/video/c/

Originally published in Spanish on the Naukas website: La piel de Orión (2015/12/10).

Outreach

In this page you will find the outreach articles based on papers of our group since 2015. They are mainly articles published in Spanish and translated into English.

Old and new

Funambulist stars

But… what happens in those globules?

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

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

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

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

Molecular detectives

The big yellow void…

Baby, baby, baby, light my way

Calibrating the Submillimetre Sky

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

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

IK Tau, an “oxygenated” death

The Bug Nebula* and the (no) One Ring

The dust trap

Flatulence in Space (III)

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

Second generation planets?

“Gas on the rocks”: shaken, not stirred

IRC+10216 returns: “Leave me alone!”

Who’s so tEMErarious in the fierce Orion?

Flatulence in Space (II)

Orion’s skin

Flatulence in Space (I)

Cyanogen: a poison, a comet and a Jedi story

IRC+10216 asks for respect for her privacy

Twenty years is nothing (for silicon carbide)

A surprisingly abundant radical

Surprises in the Rotten Egg Nebula

Hydrocarbon open bar in Orion

Something smells rotten… in Orion KL

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Flatulence in Space (I)

A few months ago, from Astromol’s facebook, we posed a challenge: if we were able to reach four hundred followers, we would write more reports on stinky gases in the universe. And we got over them. So here are these “spatial flatulences”, today focused on hydrogen sulfide.

“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.

Today we’re going to start a series of stinky gases with a gas that seems to be in a lot of places: hydrogen sulfide. 

Tell me what you smell… and I’ll tell you what you’re made of

Olfaction is a sense to which we generally pay less attention than others such as sight or touch. However, it has been shown to have an important evocative capacity and its in-depth study earned a shared Medicine Nobel Prize in 2004. Regardless of what that might mean in terms of neural connections and olfactory memories, it’s clear that odors (unless we have a problem) catch our attention.

So, realizing that some of the gases we discovered in space, here on Earth smell terrible, we decided to get down to work and learn a little more about them. The surprise came when we compared the information and saw that many gases smell of something rotten (whether it’s eggs, fish or whatever). And, at the top of the eschatological, some of those gases detected in space are also present in flatulence.

Apparently, the worst in both worlds, the most nauseating, are hydrogen sulfide (which provides the “mixture” with a rotten egg-like smell) and carbonyl sulfide. They are joined by other sulfur compounds. They also contain methane, but keep an eye on appearances: methane has no smell at all, so we won’t discuss it in this report (just as we won’t talk about the problems humans suffer in their bellies when there’s excess gas).

Hydrogen sulfide (H2S) is a nasty piece of work with its good side produced in both biological and industrial processes. When in aqueous dissolution it is called hydrogen sulphide and, as gas, it is smelly, toxic, flammable, colorless and very stinky. It is usually in the environment in very, very small amounts (normal environmental content is 0.00011 to 0.00033 parts per million (ppm). As always, the quantity will determine the toxicity of a product.

Our protagonist is a gas somewhat heavier than air and is found naturally in volcanoes, in springs, in stagnant waters, drains, swamps, wells, sewers…  In fact, if it bubbles up from the bottom of a lagoon and you’re unlucky enough to breathe it when it comes to the surface, you may stay in place forever. Just like if you enter a decaying fish warehouse that has been closed long enough to release it into the environment. If there is not too much (but very little, about 5 ppm) it will irritate your throat, eyes and entire respiratory system, but apparently, 20-50 ppm in the air is enough to cause you acute discomfort and, unlucky, drive you to the boatman’s arms.

Besides, hydrogen sulfide is a little misleading. According to this company that, among many other things, makes drilling, in large concentrations this gas becomes odorless… What a cheater. And what a deception for us who thought he was a loyal stinker. But wait… it’s not really that it loses its smelly character: it is that in large quantities it nullifies our olfactory capacity and we stop smelling it. If this happens, bad sign.

We could keep talking about hydrogen sulfide as a lethal agent, but let’s move on to reveal other things related to its discovery in space: it’s not all going to be bad, it also has other good things (or just characteristics inherent to it, in science we’re not manichean).

Discovery and transdisciplinarity

It was 1972 when P. Thaddeus, leading a five-person research team, discovered the presence of hydrogen sulfide in the interstellar medium. He used the 12-meter telescope at Kitt Peak National Observatory (USA). This work detected this compound in seven sources studied in our galaxy, the Milky Way [1]. They estimated that the abundance of hydrogen sulfide was similar to that of formaldehyde, but had to wait until 2005 for Comito et al. to conduct an in-depth survey and determine its abundances.

By the way: the 1972 article was also signed by an A. A. Penzias and another R. W. Wilson. Do those names ring a bell? Six years later, both of them, working at Bell Telephone Laboratories, would receive the Nobel Prize for discovering, in 1965, the radiation from the cosmic microwave background. What does this have to do with astrochemistry? Well, a lot.

In 1950, Gerhard Herzberg published a book in which, without being too aware of it, he gave the keys to what would later become an impressive discovery: the echoes of the Big Bang, embodied in the radiation of the cosmic microwave background.

Many had predicted the temperature of the cosmic microwave background, but Herzberg gave the key when talking about a temperature of ‘2.30 K’, obtained from measuring the intensity of cyanide radical (CN). Regardless of this veiled discovery, he received a Nobel Prize in 1971, but not for this matter, but for his work related to free radicals, of which he determined his electronic structure and geometry. It is also known for being the main promoter of molecular spectroscopy, which today allows to study the properties and behaviors of molecules. We can say he was one of the fathers of modern Astrochemistry.

However, this detail about a certain residual temperature, which he mentioned in his work “Molecular spectra and Molecular structure”, went unnoticed, hidden behind his own commentary, defining it as something with a “restricted meaning”[2]. As a result, it would be Penzias and Wilson who would make the definitive association between that temperature and the cosmic microwave backround.

In the words of José Cernicharo, researcher at CSIC, “had there been greater collaboration between astronomers and spectroscopists, this data would have caught the attention of the experts, advancing the discovery fifteen years”. Hence the importance of transdisciplinarity, collaboration between very different fields, to achieve together answers to so many questions. This is what is promoted from projects with Astromol or Nanocosmos, in which astrophysicists, astrochemists, laboratory experts, engineers, etc., come together for the same purpose: to know more about the chemistry of the universe.

But let’s go back to hydrogen sulfide. 

As we said, it was P. Thaddeus who, along with his team, detected hydrogen sulfide in the interstellar medium in 1972. Nearly twenty years later, in 1991, Bockelee-Morvan and collaborators detected hydrogen sulfide at Austin’s comet and subsequently identified its presence on Halley’s comet [3]. Recently, it has also been detected in Rosetta’s comet, 67P/Churiunov-Gerasimenco. [4]

The presence of hydrogen sulfide in comets can tell us about the formation of the comet’s own nucleus and the material that made up the nebula from which the Sun and the planets of the Solar System formed. That is, it gives us information about what materials were originally in that molecular cloud. An interesting fact from this work reveals that hydrogen sulfide detected in Halley’s comet is a parental compound.  

Let’s explain: when a comet (an ice, rock and dust ball) heats up, the matter that makes it up  starts to sublimate (it goes directly from solid state to gaseous state, without going through the liquid state). But this happens in several phases.

The primal matter that is solid in the comet, sublimates forming the coma (a cloud of gas and dust surrounding the comet). In this case we are talking about parental compounds that have sublimated directly from the comet without any chemical transformation. In the coma, however, parental compounds can undergo chemical transformations resulting in “daughter” species, which, having been processed, lose the informational value on the original composition.

Well, as we said, hydrogen sulfide in these comets seems to be “parental”, that is, it is there from the beginning of its formation. 

Isn’t that amazing? Yes, ladies and gentlemen: the hydrogen sulfide of your flatulence, the one in comets, the one that swarms through the interstellar medium, comes from the same mother cloud. So, when they smell like rotten eggs and the person sitting next to you seems a little uncomfortable, think the universe is a set of wonders… (and that maybe the one who released the gas has had a bad day).  

To be continued.

Notes:

[1]. The sources were: Orion A, W51 and in the DR21(OH) region.

[2] “From the intensity ratio of the lines with R = 0 and K = 1 a rotational temperature of 2.3º K follows, which has of course only a very restricted meaning”. From the book “Molecular spectra and Molecular structure”, Gerhard Herzberg.

[3] Eberhardt discovered the presence of H2S on Halley’s comet analyzing data from the Giotto probe, while Roesler et al. discussed the possible presence of hydrogen sulfide in Io, the Jupiter’s satellite.

[4] Organic molecules have also been detected, but none with sulfur. It is described in this work with Spanish participation: “Organic compounds on comet 67P/Churyumov-Gerasimenko revealed by COSAC mass spectrometry”.

Image:

Spacefill model of hydrogen sulfide. Based on file:Hydrogen-sulfide-3D-vdW.png by user:Benjah-bmm27, Wikipedia.

Links:

Data about H2S and its discovery in different environments on the www.astrochymist.org webpage.

NIOSH Pocket Guide to Chemical Hazards (U.S. National Institute of Occupational Safety and Health).

The Hazards of H2S Gas (hydrogen sulfide)

https://www.osha.gov/hydrogen-sulfide

Originally published in Spanish on the Naukas website: Flatulencias espaciales (I), (2015/08/03).

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Cyanogen: a poison, a comet and a Jedi story

Protonated cyanogen detected in two dark and cold molecular clouds.

For years the hypothesis has been raised that cyanogen could be an important constituent of the interstellar environment, but until now it had been impossible to confirm. Detected in Titan’s atmosphere (Saturn’s satellite) and in the tail of Halley’s comet (although, in this case, it was other compound in the cyanogen family than the one in our history), its finding caused not a few “end-of-the-world” advertisements in 1910. And while it is extremely toxic to humans, science fiction has made cyanogen a habitat for fictional creatures: the Celegians. Together, they form a triad of stories.

Cyanogen (NCCN) is the simplest member of the dicyanopolyynes series. Its name means “what produces cyanosis” (in short, if you breathe it, you turn blue like a smurf of a bad suffocation). It smells like almonds and is colorless. And, as we said, very toxic, so don’t even think about playing with this gas.

This compound has been observed in the infrared range in Titan’s atmosphere, which is rich in nitrogen and carbon compounds, and is believed to be an important species in comets. In fact, let’s make a subsection to tell you the first of our three stories.

The Assasin Comet

Take a sit. Year: 1910. From the Yerkes Observatory, a team of researchers discovers that Halley’s tail has “cyanogen”. The news was published as a small column in The New York Times, but it was not scientific news.

The headline read: “Comet’s poisonous tail”, and after a very brief introduction to cyanogen detection on a spectrum carried out from the Yerkes Observatory, the cataclysm that would mean that Halley’s tail, laden with lethal cyanogen, entered Earth, ravaging all known life. “Cyanogen is a very deadly poison, a grain of its potassium salt touched to the tongue being sufficient to cause instant death. In the uncombined state it is a bluish gas very similar in its chemical behavior to chlorine and extremely poisonous.” The astronomer “Prof Flammarion is of the opinion that the cyanogen gas would impregnate the atmosphere and possibly snuff out all the life on the planet.”

For Marcelino Agúndez, researcher at the ICMM-CSIC (we will talk about him in this article), “Mr. Flammarion was quite a character in his day, but we cannot forget that, in addition to astronomer, he was spiritualist and quite fanciful. Scientifically, it is not argued that gas from the tail of a comet like Halley, whose closest distance to Earth at the time was about 22.4 million kilometers, could not even be mixed with our atmosphere. Fortunately today we know a lot more about these issues.”

Whoever wrote the New York newspaper article had no choice but to add the opinions of other specialists (astronomers) who claimed the classic “I’m afraid not”: “Most astronomers do not agree with Flammarion, inasmuch as the tail of a comet is in a state of almost inconceivable rarification, and believe that it would be repelled by the mass of the earth as it is by the light of the sun. Also it is considered probable that the cyanogen of the comet’s tail on contact with the earth’s atmosphere would be decomposed by combustion into nitrogen and carbon dioxide, in quantities quite harmless to animal life.”

Luckily.

Protonated cyanogen

In this article from “The New York Times” they didn’t really refer to exactly the same species we’re going to talk about now, but to the cyanide radical (CN), that is sometimes called cyanogen.

Apart from its toxic characteristics, and already entering our second history, which centers on Astrochemistry, some hypotheses raise that this family of molecules can be an important constituent of the interstellar and circumstellar medium, but it is very difficult to corroborate this theory because observations do not allow us to detect them clearly.

This is because this species does not have a stable electric dipole moment and therefore has no rotation spectrum so it cannot be detected by radio techniques.

And why do we talk about cyanogen if we can’t detect it? Because a research team, led by Marcellin Agúndez (researcher of the Molecular Astrophysics Group of ICMM-CSIC) set out to confirm its presence in molecular clouds using indirect techniques. Analyzing data obtained with both the 40 meter Yebes radio telescope and the IRAM30m radio telescope, and applying chemical models [1] developed by this multidisciplinary team, they searched for the protonated “cousin” of cyanogen. Finally, the team has obtained the first solid evidence of the presence of protonated cyanogen (NCCNH+) [2] in the cold dark molecular clouds TMC-1 and L483.

The protonated species is polar and can be observed in the range of radio waves. Although protonation can change its properties, it helps us to know that the molecule is there. The bottom line is that cyanogen (NCCN) could have an abundance comparable to that of other abundant and decades-known species such as hydrogen cyanide (HCN).

In short: it was hard to spot it, but now we know that there is cyanogen in the interstellar medium.

Celegians

And to close this strange triad, the third story is pure science fiction, because you have to know that there are some living beings that appear in the comics of the Jedi stories of “Star Wars” for whom cyanogen is like oxygen to us. These are the Celegians, strange creatures (forgive me the geek-purists, but I don’t quite know how to call them) similar to the octopuses (or brains with legs) that breathe cyanogen and, to leave their planet, have to live in a tank full of that gas.

If the authors of the comic had known in time, they would not have made these beings merely live in a tank, as they could walk through the interstellar environment or the atmosphere of Titan as cool as a cucumber. Well, maybe not so cool, but we could let them try and see what happens.

More information:

Paper: “Probing non polar interstellar molecules through their protonated form: Detection of protonated cyanogen (NCCNH+)”.

Notes

[1] The chemical model predicts an abundance ratio of NCCNH+/NCCN of ~ 10-4, implying that the abundance of cyanogen in dark clouds could be as high as (1-10) x 10-8  compared to H2, i.e. comparable to that of other abundant nitriles such as HCN, HNC and HC3N.

[2] Protonated cyanogen (NCCNH+) has been identified through rotational transitions J = 5 – 4 and J = 10 – 9.

Images:

Originally published in Spanish on the Naukas website:  El cianógeno: un veneno, un cometa y una historia jedi (2015/07/21).

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IRC+10216 asks for respect for her privacy

In statements made to “The Life of the Stars”, the hottest “celebrities” program of the moment, the IRC+10216 circumstellar envelope has declared to be fed up with being persecuted by the paparazzi.

Distribution of matter around IRC+10216.

It’s been a few years since IRC+10216 rose to fame for going through a rather tumultuous moment in her life. However, in the latter stages, she confesses to being already very fed up with paparazzi’s persecution, who insist (in a way that becomes strenuous) to make known every detail of her daily existence. “I’m especially tired of such an ALMA, it doesn’t leave me alone,” she says angrily. 

Apparently, such “ALMA” has penetrated its intimacies to limits that exceed molecular sizes. Readers of heart magazines and social media users have made multiple comments about it, even with sometimes unwise tweets. “She is dangerously close,” said Luis Velilla (who is causally an astrophysicist and studies stars of this kind) after learning of her statements and her exhausting. Other tweets say “That happens to you for going star” or “as an audience, we don’t like to stay on the surface, we like to go beyond the envelope”.

ALMA, the “paparazzi” of the coldest stars

We have contacted ALMA, the paparazzi of the coldest stars, to find out her opinion. “I was working on cycle zero, which was a bit like my baptism of fire, and I gave to look closely at the celebrity I had closest. Others are dedicated to hot stars. I’m more into evolved, colder stars, who have a lot to tell but who hide their intimacy insistently. It was an impressive challenge for me. It’s not my fault she’s around and she’s a (role) model.”

The last assault on her intimacy perpetrated by ALMA and made public has been the one that has revealed  in detail how silicon is distributed in IRC+10216.

How did this happen?

In the spring of 2012 IRC+10216 was in her things when she realized she was being watched. She had been of interest to the pink press before. But this time it was different. ALMA’s ability to get “to the kitchen” was impressive. As if it were an impressive telephoto lens, ALMA draw with unprecedented precision the map of the distribution SiS, SiO and  SiC2  in the envelope of  this evolved star [1].

For us, who are very gossipy, this has been a real bomb, since knowing the inner parts of IRC+10216 in such detail is very revealing: in particular, the lines of high vibrational levels [2] of SiS come from a very warm region, an area very close to the star with which IRC+10216 maintains a special relationship. This is CW Leonis, who ended up making these statements:

“Yes, IRC+10216 and I have a very close relationship since I reached mature age. This is what happens to evolved stars: we eject the material to the outside in the form of layers. I will not deny it: something special has been born between us. My envelope and I are very close.”

This is not dirty laundry, this is molecules

Penetrating IRC+10216 to the limits with CW Leonis, as if it were the layer of an onion, we stumbled upon SiC2, but this molecule mysteriously disappears as we walk away to, oh surprise, reappear in a thin layer quite far from the star.  This may be due to the capabilities of ALMA [3].

As for SiO, it has a certain extensive and elongated structure. What could this be about? Explaining elongation is very speculative, but it gives rise to interesting ideas.

First, it could be the presence of a dust “belt” in the direction of elongation. This could cause more gas to form due to increased density in that area. Or, maybe, there is a companion star orbiting CW Leonis. This companion star could also create a preferred direction (the plane of the orbit) for material accumulation and increased density, favoring molecular formation. Although it could also be a molecular jet. For now, it’s all assumptions.

For ALMA this has just begun: “I am now finishing cycle two. If in cycle zero I was learning, now I’m taking a wagon: I’ve learned to use my tools and now there’s no one to stop me.”

IRC+10216 has stated that it will continue to grant exclusives as long as the privacy of its relationship with CW Leonis is respected (on the possible companion star she said not much, but it will undoubtedly be another of the hot topics of the “stellar summer”). The most chic community looks forward to news about this relationship that so many articles are generating in the pinker press (scientific, of course).

More information

Paper: “Si-bearing molecules toward IRC+10216: ALMA unveils the molecular envelope of CW Leo” (DOI: 10.1088/2041-8205/805/2/L13).

Notes

[1] Detailed maps of the SiS, SiO and SiC2 distribution have been carried out in IRC+10216. In particular, rotational transitions were observed and not only in the fundamental vibrational state, as the detected even SiS rotational transitions of high vibrational levels (v-7) and tentatively (v-10).

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

[3] There is some loss of flow (emission) in the outer thin layer because it has a very large size. This is because in ALMA (and any other interferometer) exists what is called an MRS (Maximum Recoverable Scale), the maximum recoverable scale. This means that any actual structure that is larger than a given formula is filtered and we lose much of its emission.

Images

Image 1: This image shows the central section of a series of images that, as in a scan, allow us to distinguish the distribution of matter around the star IRC+10216. The data for composing this image has been obtained by the IRAM 30m telescope and was developed for the article Molecular shells in IRC+10216: tracing the mass loss history“.

Image 2: ALMA, the “paparazzi” of the coldest stars. Credit:  ESO/B. Tafreshi  (twanight.org)

Originally published in Spanish on the Naukas website:  IRC+10216 pide respeto a su privacidad (2015/07/16).

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Twenty years is nothing (for silicon carbide)

Gardel’s tango “Volver” sounds, the one that I like so much and to which I have resorted on occasion for its temporal implications, and I arrive at that part in which he sings that “twenty years is nothing”.  And hearing it I can’t help but remember the SiCSi molecule and silicon carbide (SiC, not to be confused with  sic). All because, in the 1990s, scientists were already talking about SiCSi as a missing link in the formation of silicon carbide and that there should be a lot in the most intimate and hidden regions of carbon-rich dying star envelopes. But it took twenty years to be able to confirm this by astronomical observations.

Circumstellar enveloppe IRC+10216

The SiCSi molecule is formed by two silicon atoms and one carbon atom. The fact that it has been called a ‘missing link’ is simple, although we have to explain it step by step.

For starters, we go back to our fetish envelope, which is providing a huge amount of information to astrochemists. We’re talking about the envelope of the star CW Leonis, also known as IRC+10216. Let us remember that it is an evolved star, a star that has begun the final phase of its life, ejecting into the environment the matter that composes it in the form of layers. At the end of its life it will form a planetary nebula and, at its center, there will be a white dwarf star. But there´s still a long way to go to reach that point.

About 400 light years from us, this star is one of the brightest infrared sources in the sky and, thanks to its proximity, we can study its envelope in great detail (and more since we have tools and data with Herschel and ALMA). IRC+10216 has been found to be exceptionally rich in molecular species (in fact, half of the known interstellar and circumstellar species have been observed in this carbon-rich envelope). But astrochemistry has an interdisciplinary way of working: observations are not enough; you have to corroborate the information in a laboratory.

The laboratory

Before interpreting astronomical observations, astrochemistry looks for answers in laboratories. This is where they work to characterize molecular species and chemical processes, emulating the conditions that occur in very specific environments (such as the envelopes of evolved stars or the interstellar medium).

Experts had been trying to “catch” the SiCSi molecule for many years, but it took a long time. After numerous attempts, McCarthy et al. (2015, Harvard University) managed to synthesize and characterize it in the laboratory, allowing the community to confirm that what was seen in the astronomical  observations  was, indeed, the molecule SiCSi. It was finally possible to put a name to those lines obtained by the team of astronomers of Astromol/Nanocosmos: in total,  112 lines of this molecule in the spectrum of IRC + 10216 using data from the  IRAM 30m radio telescope  [1].

By obtaining such an accurate spectroscopic characterization, it was possible to validate the hypothesis that this molecule is abundant in this type of environment, where it is very likely to play a fundamental role in the early stages of formation of silicon carbide (SiC) powder grains. However, many unknowns remain about that role.

How are dust grains formed?

We know that dust grains, an ubiquitous component in the interstellar medium of galaxies, are synthesized mainly in two types of sources: in the internal winds of AGB stars (Asymptotic Giant Branch) [2] and in the ejection of massive stars when they explode as supernovae.

In supernovae different types of dust can form depending on the degree of enrichment in heavy elements, although the effectiveness of dust formation in supernovae is still a matter of debate (in fact, recent studies with the Herschel Space Telescope suggest that the masses of dust formed are much greater than previously thought).

The formation of dust grains can be simplified by explaining it as a two-stage process: first the “seeds”, called nucleation seeds, are formed from gas-phase species composed of chemical elements of a high refractory character. When we talk about refractory character we refer to those chemical elements that, below a certain temperature (the higher the temperature the greater the refractory character), tend to disappear from the gas phase and participate in the formation of solid condensates.

The second stage involves the growth of the grain: on the nuclei formed, compounds of a certain refractory character are condensed (in theory, less refractory than the elements that have formed the nucleus). That is, after forming a small nucleus, atoms and molecules are glued to it.

There are still many mysteries in this sequence of events, starting with the fundamental step of the formation of the seeds of nucleation, in which simple species in the gas phase are added to form nanoparticles. In fact, that’s one of the goals of Nanocosmos – to recreate this process in a lab to learn more about how those dust grains are born.

Silicon carbide (SiC): grain versus molecule

Silicon carbide (SiC) grains are abundant in space. In fact, their presence in micrometeorites is proof of the importance of the chemistry of these compounds (SiC, Si2C and SiC2) in the environment of red giant stars [3].

That’s because micrometeorites are a repository of primordial matter, since we assume that these remains formed in the same molecular cloud from which the entire Solar System emerged. If that is the case, the primordial molecular cloud could, in turn, be made up of material ejected by a red giant star [3] into the interstellar medium. This would close, for now, the cycle of silicon carbide: from a dying star to the interstellar medium, where a cloud would form from which, in turn, stars would be born that would eventually die, either as supernovae or as red giant stars, and so on. But knowing the process does not explain how silicon carbide was born.

On the one hand, it would be logical to think that the molecular precursors from which these grains of silicon carbide are born were the gas-phase molecules of silicon carbide themselves, but that does not seem to be the case.

In fact, the gas-phase silicon carbide (SiC) molecule has been detected in the outer regions of the IRC +10216 envelope (and not in the inner ones). Therefore, if it is not in the internal ones, it does not participate in the formation of the grains. In contrast, in the inner layers, where the dust is formed, the most abundant molecules containing Si−C bonds are SiC2  and the newly discovered SiCSi.

Both molecules should play a key role in the formation of grains of silicon carbide (SiC) dust. Add to this the fact that the abundance of SiCSi decreases as we move away from the star, and the data suggest that these molecules could be progressively incorporated into silicon carbide grains as they move into a colder environment.

Further deepening in this process of birth and formation of silicon carbide grains will require high-resolution interferometric observations. We still don’t know how that nucleation seed is born, whether it’s silicon carbide or any other grain of dust. Again, laboratories and frontier projects such as Nanocosmos will help us to obtain more data to draw more clearly the path of the formation of the dust grains that populate the interstellar medium and that are so important in the process of star and planet formation. Perhaps, recalling Gardel again, we should not wait another twenty years to uncover this mystery.

Notes

[1] Nine of these lines have also been detected with the  Submillimeter Array (SMA).

[2] AGB stars are stars with masses less than 8 solar masses that are in their last evolutionary stages. Since the early twentieth century it has been known that, in the photospheres of AGB stars, there are molecules such as TiO, VO, ZrO, CN, C2 and C3, among others.

[3] The presence of silicon carbide in carbon-rich AGB stars was first confirmed in the 1970s.

Article based on astromol’s press release (in Spanish): “How silicon carbide is formed“.

Links:

– Paper: “Discovery of SiCSi in IRC +10216: A missing link between Gas and Dust Carriers of Si−C Bonds”

Images:

Image 1: Large-scale structure of the circumstellar envelope IRC+10216, seen through the brightness of the J=2-1 carbon monoxide (CO) line. The observations have been made with the IRAM 30m radio telescope (Granada) and are described in the article (Cernicharo et al 2015, A&A, 575, A91). The region in which the SiCSi molecule has been found and where the formation of the dust grains takes place corresponds to the innerst region.

Originally published in Spanish on the Naukas website:  Veinte años no son nada para el carburo de silicio (2015/06/16).

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A surprisingly abundant radical

Astronomers discover the presence of interstellar ketenyl (HCCO)

Stars use to form in dark and cold clouds. But everything has a beginning. When the process of stellar formation in these clouds has not yet begun, recent research reveals that they could undergo chemical processes other than those we imagined, taking on a relevant role the grains of dust, whose action, until now, had essentially been confined to the clouds where the existence of a nascent star was already known.

Lupus 1 molecular cloud region, where the presence of the ketenyl radical has been discovered.

The molecular clouds we find in the interstellar environment are dim, seemingly empty spaces in which stars are born. It is a process by which the gas and dust contained in these clouds begin to condense and fragment at some points, collapsing with gravity and leading to protostars. There are still many unknowns related to the reasons that cause this process to trigger. Therefore, molecular clouds are highly studied environments in the field of Astrochemistry.

Recently, a team of researchers has studied nine of these dark clouds using data obtained with the IRAM 30m radio telescope. Among them were both dark and cold clouds without stellar nuclei, as well as molecular clouds in which the birth of a protostar has already taken place.

Detailed analysis of these observations has revealed, for the first time, the presence of ketenyl radical (HCCO) in both the dark and cold cloud core Lupus-1A [1], in which there is still no indication of the presence of a protostar, and in the molecular cloud L483, which has a protostar inside.

In addition, ketene (H2CCO) and acetaldehyde (CH3CHO) molecules have been found in these two sources and in three more dark clouds. Finally, formyl radical (HCO) has been detected in the nine sources (which has been a surprise) and propylene (CH2CHCH3)[2] in four of the observed clouds, significantly expanding the number of dark clouds where these molecules are known to be present. This work has therefore presented two rather eye-catching new study fronts.

HCO, you used to be cool

The formyl radical (HCO) is usually a tracer of photodissociation regions, that is, it is found in areas where there is an intense activity of stellar formation and radiation tends to break the bonds of molecules, making the existence of complex molecules difficult. But it now seems to be confirmed that it is not only present in regions of photodissociation, but are also found in the dark and cold clouds: it has been detected in the nine clouds studied in this work. [3] So, from being a radical present only in active areas, now it has become present in both environments, losing his exclusivity.

Cold dark cloud gas phase chemical models can reproduce the observed abundances of HCO, but they cannot explain the presence of ketenyl radical (HCCO) in Lupus-1A and L483 and the high abundance derived from propylene.

HCCO, insistent ketenyl

The real discovery has been to know the abundance of ketenyl radical. Normally a radical is expected to be less abundant than its stable counterpart, in our case ketene. This is because radicals are chemically more unstable and reactive.  

But in both Lupus-1A and L483, ketenyl radical is only about 10 times less abundant than ketene, indicating that there must be an effective mechanism for forming this radical. And one more fact: the ketenyl radical (HCCO) found in Lupus-1A and L483 is a missing link in the HxC2O series. [4]

Cloud with star, cloud without star

Organic molecules are ubiquitous in interstellar clouds. The most complex and saturated are found in clouds inside which stellar objects are forming. The energy released by the forming star is the engine that causes the chemical machinery to become operational, allowing the thermal evaporation of  molecules frozen on the surface of the dust grains. 

But, in dark cold clouds where there are no stellar nuclei yet, the chemical composition is characterized by being simpler and more unsaturated: highly unsaturated carbon chains are found in the polyyne and cyanopolyyne families, as well as relatively simple oxygen-carrying organic molecules, whose synthesis depends to a large extent on the chemical processes that take place in the gas phase. As there is no star, there is no evaporation of ice in the dust grains.

However, the frequent presence of methanol (CH3OH) in cold dark clouds and the most recent detections of other complex and saturated organic molecules such as propylene (CH2CHCH3), methyl formicate (CH3OCOH), dimethyl ether (CH3OCH3), methoxyl (CH3O) and formic acid (HCOOH), have put on the table the role of reactions on the surface of dust grains and non-thermal desorption processes in these cold and seemingly calm environments.  

In short, the dark and cold clouds, in which stars are not yet forming, could undergo chemical processes other than those we imagined, taking on a relevant role the grains of dust, whose action, until now, had essentially been confined to the clouds where the existence of a nascent star was already known.

It is clear that, in light of these new observational results, it will be necessary to review the chemistry of cold dark clouds. We need in-depth observational studies capable of expanding both the number of chemically characterized sources and the inventory of identified molecules. All because, until now, we thought the ices slept peacefully on the dust grains if there was no heat to wake them up.

More information:

This work has been published in the scientific paper Discovery of interstellar ketenyl (HCCO), a surprisingly abundant radical, whose authors are Marcelino Agúndez (Institute of Materials Science of Madrid-CSIC, Spain);  José Cernicharo (Institute of Materials Science of Madrid-CSIC, Spain); and Michel Guélin (Institute de Millimetric Radioastronomy, IRAM, France).

Notes:

[1] Located in the constellation Lupus (the wolf), this area was discovered by Sakai et al. (2010). This starless core in the molecular cloud of Lupus has a chemical richness comparable to that of the widely studied TMC-1 cloud and provides an excellent opportunity for the study of dark cloud chemistry.

[2] Formyl radical (HCO) had only previously been detected in L1448, B1 and TMC-1, and propylene (CH2CHCH3), only in TMC-1. 

[3] Perhaps it was because until now the searches had been carried out at other wavelengths. 

[4] Many of the organic oxygen-carrying molecules observed in the dark clouds can be described by the general formula HxCnO, with n = 1 (CO, HCO, H2CO, CH3O, y CH3OH), n = 2 (C2O, H2CCO, and CH3CHO), andn = 3 (C3O y HCCCHO). The formation of most of them is reasonably explained either by chemical reactions of the gas phase (with notable exceptions as in the case of CH3OH). That’s why ketenyl radical (HCCO) is considered to be a missing link in the HxC2O series.

Images:

Lupus 1 molecular cloud region, where the presence of the cetenyl radical has been discovered. Credits: Apo TEC140 (140/f7.2) – FLI Proline 16803 – L (340m) R (120m) G (120m) B (120m) – Warrumbungle Observatory, Coonabarabran, NSW, Australia.

Originally published in Spanish on the Naukas website: Un radical sorprendentemente abundante (2015/05/22).