Shusuke Utsumi
Theory Astrophysics Lab in Nagoya University, Japan

Abstract
Smoothed Particle Hydrodynamics (SPH) offers a powerful way to
study formation processes across a wide range of astrophysical systems.
I will present two applications from brown dwarfs to rocky planets where
advanced simulations are challenging established theories.

First, we test the idea that brown dwarfs form when two circumstellar
disks pass close enough to create collapsing gravitational "bridge
structures." Our SPH simulations show that this mechanism requires
unusually massive disks and extremely close encounters, conditions that
are both rare. We therefore find that disk encounters are unlikely to be
a major brown-dwarf formation pathway.

Second, I introduce a new SPH-based Lagrangian method for modeling
collisions of rocky bodies. By representing elastic stresses through
central forces rather than evolving a full stress tensor, the scheme
conserves angular momentum exactly while greatly reducing computational cost.
This enables more realistic simulations of asteroid-shape
evolution, fragmentation, and early planet-building collisions.

Together, these studies illustrate how advances in SPH methods can
improve our understanding of both substellar formation and the
collisional growth of rocky planets.

2026 January 14, 13:30

IA/U.Porto
Centro de Astrofísica da Universidade do Porto (Auditorium)
Rua das Estrelas, 4150-762 Porto