![Snapshots of the system 1 ps after the initial contact of the nanograins for different initial velocities. Atom colour key indicates hydrogen: white; carbon: dark gray; oxygen: red; silicon: beige; and magnesium: green. -- [astro-ph.GA]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/07/When-Two-Worlds.png?fit=1200%2C671&ssl=1)
[astro-ph.GA] Our overall objective is to determine how collision velocity governs the interactions between silicate and carbonaceous nanograins. (astrochemistry)
We aim to: i) identify collisional regimes capable of producing mixed silicate-carbonaceous grains and/or chemically complex molecular species, and ii) quantify fragmentation threshold velocities related to dust destruction. We performed molecular dynamics simulations employing a machine-learning force field to model head-on collisions between silicate and carbonaceous nanograins of comparable masses. Collision velocities span 1 – 11 km/sec.
For all collisions, we tracked the extent of grain-grain mixing and the formation of molecular fragments. We identified four velocity regimes: 1) <1.5 km/sec, where grains bounce off one another, 2) 1.5-3.5 km/sec, where sticking between the grains starts to occur, 3) 3.5-7.5 km/sec, where grains tend to aggregate and form inter-grain chemical bonds, yielding stable mixed grains, and 4) >7.5 km/sec, where fragmentation dominates.
The latter regime produces CO as the main product, along with hydrocarbons, complex organic molecules, molecular silicates, and mixed carbonaceous-silicate clusters. The fragmentation threshold velocity for these collisions is approximately 7.5 km/sec. We show that collision velocities govern both the physical and chemical outcomes of silicate-carbonaceous nanograin interactions.
In the fragmentation regime, collisions provide a viable pathway for generating mixed grains and a wide range of molecular species, many of which have been observationally detected. Here, we provide a simple credible mechanism linking the physics of grain processing with observed complex interstellar chemistry.
Alexandros Kyriazis, Albert Rimola, Stefan T. Bromley
Comments: Accepted in A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2607.22213 [astro-ph.GA] (or arXiv:2607.22213v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2607.22213
Focus to learn more
Related DOI:
https://doi.org/10.1051/0004-6361/202661452
Focus to learn more
Submission history
From: Stefan Bromley
[v1] Fri, 24 Jul 2026 11:31:33 UTC (5,206 KB)
https://arxiv.org/abs/2607.22213
Astrobiology,
