The formation of stars and planetary systems is a complex phenomenon that relies on the interplay of multiple physical processes. Nonetheless, it represents a crucial stage for our understanding of the Universe, and in particular of the conditions leading to the formation of key molecules (e.g. water) on comets and planets. Herschel observations demonstrated that stars form in gaseous filamentary structures in which the main constituent is molecular hydrogen (H2). Depending on its nuclear spin H2 can be found in two forms: 'ortho' with parallel spins and 'para' where the spins are anti-parallel. The relative ratio among these isomers, the ortho-to-para ratio (OPR), plays a crucial role in a variety of processes related to the thermodynamics of star-forming gas and to the fundamental chemistry affecting the deuteration of water in molecular clouds, commonly used to determine the origin of water in Solar System bodies. Here, for the first time, we assess the evolution of the OPR starting from the warm neutral medium by means of state-of-the-art 3D magnetohydrodynamic simulations of turbulent molecular clouds. Our results show that star-forming clouds exhibit a low OPR (≪ 0.1) already at moderate densities (∼1000 cm-3). We also constrain the cosmic-ray ionisation rate, finding that 10-16 s-1 is the lower limit required to explain the observations of diffuse clouds. Our results represent a step forward in the understanding of the star and planet formation processes providing a robust determination of the chemical initial conditions for both theoretical and observational studies.

Lupi, A., Bovino, S., Grassi, T. (2021). On the low ortho-to-para H2ratio in star-forming filaments. ASTRONOMY & ASTROPHYSICS, 654(1 October 2021) [10.1051/0004-6361/202142145].

On the low ortho-to-para H2ratio in star-forming filaments

Lupi A.
;
2021

Abstract

The formation of stars and planetary systems is a complex phenomenon that relies on the interplay of multiple physical processes. Nonetheless, it represents a crucial stage for our understanding of the Universe, and in particular of the conditions leading to the formation of key molecules (e.g. water) on comets and planets. Herschel observations demonstrated that stars form in gaseous filamentary structures in which the main constituent is molecular hydrogen (H2). Depending on its nuclear spin H2 can be found in two forms: 'ortho' with parallel spins and 'para' where the spins are anti-parallel. The relative ratio among these isomers, the ortho-to-para ratio (OPR), plays a crucial role in a variety of processes related to the thermodynamics of star-forming gas and to the fundamental chemistry affecting the deuteration of water in molecular clouds, commonly used to determine the origin of water in Solar System bodies. Here, for the first time, we assess the evolution of the OPR starting from the warm neutral medium by means of state-of-the-art 3D magnetohydrodynamic simulations of turbulent molecular clouds. Our results show that star-forming clouds exhibit a low OPR (≪ 0.1) already at moderate densities (∼1000 cm-3). We also constrain the cosmic-ray ionisation rate, finding that 10-16 s-1 is the lower limit required to explain the observations of diffuse clouds. Our results represent a step forward in the understanding of the star and planet formation processes providing a robust determination of the chemical initial conditions for both theoretical and observational studies.
Articolo in rivista - Articolo scientifico
Astrochemistry; ISM: molecules; Magnetohydrodynamics (MHD); Methods: numerical; Stars: formation;
English
15-ott-2021
2021
654
1 October 2021
L6
none
Lupi, A., Bovino, S., Grassi, T. (2021). On the low ortho-to-para H2ratio in star-forming filaments. ASTRONOMY & ASTROPHYSICS, 654(1 October 2021) [10.1051/0004-6361/202142145].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/332106
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