Credit: ALMA (ESO/NAOJ/NRAO)/ J. R. Goicoechea (Instituto de Física Fundamental, CSIC, Spain)
Dr. Javier R. Goicoechea is leading a new research that proves the existence of short-lived molecular cloudlets (ages less than 10,000 years and total mass of about 60 solar masses) around Sgr A*, the location of the super massive black hole at the centre of our galaxy. This research has revealed exciting evidence of molecular gas, the fuel that forms stars, orbiting within the central parsec of the Milky Way at high speeds, up to about 300 km/s. The images (1″-resolution ALMA observations, see above) reveal the small spatial scale morphology of the interstellar gas in this fascinating region and the presence of molecular “cloudlets” (less than 20,000 AU size) at about one light year from SgrA*. While it is unlikely that the observed cloudlets will directly form new massive stars, their presence is a piece of the puzzle toward understanding the formation of stars close to supermassive black holes. The above image is ESO’s Picture of the Week (see below).
More information:
This research was presented in the paper “High-speed molecular cloudlets around the Galactic center’s supermassive black hole“, published in Astronomy and Astrophysics Volume 618, A35 (19pp), 11 October 2018. The authors are: Javier R. Goicoechea (Instituto de Física Fundamental, IFF-CSIC, Madrid, Spain), Jerome Pety (Institut de Radioastronomie Millimétrique (IRAM), France), Edwige Chapillon (Institut de Radioastronomie Millimétrique (IRAM) and OASU/LAB-UMR5804, CNRS, Université Bordeaux, France), José Cernicharo (Instituto de Física Fundamental, IFF-CSIC, Madrid, Spain), Maryvonne Gerin (Sorbonne Université, Observatoire de Paris, France), Cinthya Herrera (Institut de Radioastronomie Millimétrique (IRAM), France), Miguel A. Requena-Torres (Department of Astronomy, University of Maryland, USA) and Miriam G. Santa-Maria (Instituto de Física Fundamental, IFF-CSIC, Madrid, Spain).
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 sphericalshell
“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, VLAand 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.
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
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).
