Pablo del Mazo Sevillano, new doctor

On January 25th 2021, Pablo del Mazo Sevillano has defended in the Autonomous University of Madrid his PhD work entitled “Superficie de energía potencial y dinámica para la reacción H2CO + OH” (Potential Energy Surface and Dynamics for H2CO + OH reaction) supervised by professors Octavio Roncero Villa (IFF-CSIC) and Alfredo Aguado Gómez (UAM). Congratulations!

In this text, he explains the content of his tesis:

“The mechanism by which complex organic molecules (COMs) are found in the dense molecular clouds in the interstellar medium (ISM) has been assumed to proceed through their formation on ices. Later, as these ices evolve to hotter regions, the COMs would be released to the gas phase. Nevertheless, this complex organic molecules have been found in cold regions, shielded from UV-radiation, so it is mandatory to rethink this process.

One possible explanation comes from the results shown by CRESU experiment. In particular, it has been found that reactions between COMs and OH exhibit a huge increase in their kinetic rate constants as temperature decreases, what is surprising for reactions that usually present a barrier, hence should have an Arrhenius-like behavior. This opens the possibility of gas phase reactivity that has been previously dismissed. Unfortunately, there is no current experimental setup that can reproduce the conditions found in the ISM, in particular, the low pressure, so it is not possible to calculate the zero-pressure kinetic rate constants to be used in the astrochemical models. It is here that we can take some advantage from the computational simulations, since it is much easier to reproduce this low pressure conditions. In this PhD work we have focused on the simulation of the reactive process between H2CO + OH to form HCO + H2O and HCOOH + H, to evaluate the zero-pressure kinetic rate constants and provide a dynamical explanation of its behavior with temperature.

The dynamical simulation of a reactive process usually involves two steps:

First we must obtain the potential energy surface (PES) of the process. The PES is a function that encodes the energy for every nuclear configuration the system can reach during the simulation. It is from this function that the classical forces the system experience emerge, so a correct description of this function is crucial. In this work we have explored and propose different methodologies to express this function, with special interest in the use of artificial neural networks (ANN). ANNs are functions that present huge flexibility along with a short evaluation time, what makes them an excellent alternative to describe a PES.

The second step is the dynamical simulation itself. Once the interactions between particles are known (the PES) it is possible simulate collisions between the reactive partners and determine whether they react or not. From this, the kinetic rate constant can be calculated. In this work we have employed two methods: a quassiclassical  trajectory  method (including the zero-point energy of the reactants only at the beginning of dynamical calculations) and a Ring-polymer Molecular dynamics (RPMD) method (based on path integral and including quantum effects through the use of replicas or beads), to include quantum effects important at the low temperatures considered,  such as zero-point energy and tunneling. We found two key aspects that explain the increase of the kinetic rate constant for HCO + H2O formation as temperature lowers. On the one hand, due to the permanent dipole moment present in both reactants there is a very efficient capture mechanism at long distances. That way, reactants that are far away feel each other and start approaching until they finally collide. On the other hand, during this approach and finally collision, translational energy is transferred to rotation and vibration. This means that once the energy transfer is produced, it is not so easy for the system to redissociate back to reactants and the system gets trap for long times in a reactive complex. During this time the system has plenty of time to explore the configuration space, increasing the probability that reaction may take place. This is the mayor reaction mechanism for temperatures below 200 K, as has been found both experimentally and theoretically. Above this temperature, the direct mechanism becomes more important, leading to the well-known Arrhenius behavior”.

Representation of a PES (blue surface) over which a trajectory is being propagated (red line). Molecular geometries along the trajectory are shown.

Sarah Massalkhi, new Doctor

On December 18th 2020, Sarah Massalkhi has defended in the Autonomous University of Madrid her PhD work entitled “An Observational Study of Molecular Dust Precursors in Circumstellar Envelopes” supervised by professors Marcelino Agúndez and José Cernicharo (IFF-CSIC). Congratulations!

Circumstellar envelopes around evolved stars of AGB type are probably the main factories of dust in the Universe. However, we still do not understand the process that operates in these environments to convert simple gas-phase molecules into large dust grains. In this thesis, we carried out an observational study to determine the abundance of molecules that could potentially act as precursors of dust in a large sample of AGB stars using the radiotelescope IRAM 30m.

Among the main results, in C-rich AGB envelopes we find a clear trend in which the fractional abundance of SiC2, SiO, y CS decreases as the envelope density increases, which we interpret as an evidence of efficient incorporation of these molecules onto dust grains, suggesting that that they are strong candidates to act as precursors of dust in C-rich envelopes. Likewise, SiO shows the same trend in O-rich envelopes, suggesting that it actively contributes to the formation of dust in these environments. We also find that the studied molecules have different behaviors with respect to the C- or O-rich character of the envelope, with molecules like CS and SiS showing a clear differentiation between these two types of envelopes while SiO does not seem to be sensitive to the C/O ratio.

José Cernicharo, awarded with the “Miguel Catalán” 2020 prize

José Cernicharo, Researcher of the IFF-CSIC and Head of our group, has been awarded the “Miguel Catalán” 2020 Prize for his scientific career within the research awards of the Community of Madrid, “for the quality of his research, his recognized leadership at national and international level in the area of Molecular Astrophysics and for his contributions and technological innovations”.

The Community of Madrid convenes annually the Research Awards “Miguel Catalán” and “Julián Marías” to the scientific career, in order to recognize scientific activity, as well as the scientific and humanistic values developed by researchers who throughout their professional career have been in some way linked to the Community of Madrid, and the Research Awards of the Community of Madrid “Miguel Catalán” and “Julián Marías” to researchers of less than forty years , in order to recognize the quality and excellence of scientific and research work developed at the beginning of his research career. They are convened annually in the two Areas, Sciences and Humanities.

The ceremony, which will take place tomorrow, November 20 at 10:30, can be followed online through the following links:

  1. Madrid Community Canal
  2. Twitter of the Community of Madrid
  3. Complutense University Of Madrid Canal
  4. Youtube from the Complutense University of Madrid

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).

The core of galaxy NGC 1068.

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.


[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).


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.