October 2, 2025Open Access

Brown Dwarf Formation through Gravitational Collapse: Insights from 3D Numerical Simulations

Key Points

Brown dwarfs may form similarly to low-mass stars, but with a prolonged first-core phase.
The simulations employed the RAMSES code, capturing critical dynamical ranges and processes of BD formation.
Key processes include isothermal collapse, hydrostatic core formation, and H2 dissociation.
Initial brown dwarfs have radii of approximately 0.75 R⊙ and masses around 0.8 MJup, evolving through accretion.

Abstract

Abstract The formation mechanism of brown dwarfs (BDs), whether akin to stars or ejected planetary-mass objects, remains debated. We present the first 3D radiation-MHD simulations of magnetized, turbulent, gravitationally unstable low-mass cores (0.05–0.1 M ⊙ ) collapsing into proto-BDs. Using the RAMSES code with adaptive mesh refinement, we model the full dynamical range (10 5 –10 22 cm −3 ), including radiative transfer (flux limited diffusion) and nonideal MHD (ambipolar diffusion). Our simulations self-consistently follow the isothermal collapse, first hydrostatic core formation, H 2 dissociation, and BD birth. The resulting BDs have initial radii ≈0.75 R ⊙ and masses ≈0.8 M Jup , growing via accretion as we follow the early evolution of the object. Crucially, we find that BDs may form similarly to low-mass stars but with a prolonged first-core phase, supporting a starlike formation scenario.

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