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CORDIS - Résultats de la recherche de l’UE

Setting the Stage for Solar System Formation

Periodic Reporting for period 4 - S4F (Setting the Stage for Solar System Formation)

Période du rapport: 2020-02-01 au 2021-01-31

Low-mass stars like our Sun are formed in the dense regions of dark clouds of dust and gas that obscure their visible light. Deep astronomical observations at infrared and submillimeter wavelengths are uniquely suited to probe the inner regions of these young stellar objects and unravel their structures, as well as the physical and chemical processes involved. These earliest stages are particularly interesting because the properties of the deeply embedded objects reflect the star formation process itself and how it relates to its environment. It is for example during this stage that the final mass of the star and the properties of its disk – and thus ability to form planets – are determined. It is also during these stages that the first seeds for the chemical evolution of the protoplanetary disk are planted and where some complex organic, possibly prebiotic, molecules may be formed. The aim of the program is to map the physics and chemistry of the early Solar System using new high resolution, high sensitivity observations from the Atacama Large Millimeter/submillimeter Array (ALMA) coupled with state-of-the-art radiative transfer tools and theoretical simulations to address some of the key questions concerning the physics and chemistry of the earliest stages of the Solar System: How is the chemistry of the earliest protostellar stages related to the physical structure and evolution of the young stellar object and its surrounding environment? Which complex organic molecules are present in the inner regions of low-mass protostars? What are the chances the rich chemistry of the earliest stages is incorporated into planetary systems such as our own?
The action has been highly active and made excellent progress in addressing the questions outlined above. We have (i) initiated and executed programs to measure the physical and chemical conditions of the gas surrounding embedded protostars, (ii) obtained, reduced and published data from ALMA on the complex organic chemistry of embedded protostars including first detections of a number of complex organic molecules and their isotopologs and (iii) explored the link between the physical structure of protostars and their chemical signatures through sophisticated numerical simulations and detailed observations.

The nexus of the work has been a large survey using ALMA of the complex chemistry of a system of solar-type young stars. The data show a wealth of molecular lines from different species that we identify through spectroscopic data obtained in laboratories on Earth. These observations have so far resulted in a number of discoveries of molecules – some that had never been seen in the interstellar medium before and some that had only been detected in more extreme environments, for example in the center of our Galaxy.

The high-quality data also allow us to make significant progress in making detailed and accurate inventories of molecular species in these regions and address their origin. A significant effort for the team has been on synthesising this information and study the more general trends in the abundances of different molecular species and their isotopic compositions – as well as comparing gas-phase inventories to knowledge about the ice chemistry in these regions. The results of these measurements support a picture where many of these species are formed during the densest cold phases in the evolution of young stars where most of the chemistry takes place on the surfaces of dust grains. The accurate measurements also pose new challenges with respect to mimicking these results in laboratory experiments as well as through detailed chemical models.

The results also pose new questions, e.g. whether this chemistry is ubiquitous - i.e. that all forming young stars are characterized by similar chemical processes and thereby have a chemical complexity that can be incorporated in their protoplanetary disks. We have carried out observations of a number of young protostars from different star-forming regions and in different evolutionary stages, focusing on the kinematics of the gas on the scales where disks form. In particular, we find that the physical structure is of great importance for the observed molecular signatures – but not necessarily that the physical evolution itself changes the chemistry significantly.

The final aspect of the action has been to put the observations of young stars in the earliest stages in the context of the understanding of our own Solar System and its origin. By comparing the chemical structures of Solar-type protostar to measurements of Solar System comets we show that there are significant similarities between the organic contents suggesting that a significant part of the chemistry occurring in the earliest stages of star formation is inherited to the protoplanetary disk and bodies formed within it. Interestingly, the same organic composition is also seen in different regions of the Galaxy – e.g. in its center where the physical conditions are significantly different. Other indications, e.g. the isotopic composition of water and organic molecules, lend support to the notion that the Sun in fact has formed in a clustered environment.

The results of the action has been published in a long range of publications in international peer-reviewed journals, through invited and contributed presentations at international conferences as well as in press-releases presenting particularly high profile results.
The ALMA observations in themselves represent a revolution in terms of the achievable angular resolution and sensitivity critical for studying the physical and chemical processes taking place on the smallest scales toward newly formed protostars. We have been highly successful in taking advantage of this opportunity and thereby move the field beyond the previous state of the art. Likewise, the comparison between these detailed observations and the predictions from the numerical simulations are possible through the effort of developing the techniques for bridging the gap between these different fields, in particular through detailed continuum and line radiative transfer calculations.
The physical regions where complex organic molecules reside around a young protostar.