A Numerical Study of Brown Dwarf Formation via Encounters of Protostellar Disks

Abstract

The formation of brown dwarfs (BDs) due to the fragmentation of proto-stellar disks undergoing pairwise encounters was investigated. High resolution allowed the use of realistic initial disk models where both the vertical structure and the local Jeans mass were resolved. The results show that objects with masses ranging from giant planets to low mass stars can form during such encounters from initially stable disks. The parameter space of initial spin-orbit orientations and the azimuthal angles for each disk was explored. An upper limit on the initial Toomre Q value of ~2 was found for fragmentation to occur. Depending on the initial configuration, shocks, tidal-tail structures and mass inflows were responsible for the condensation of disk gas. Retrograde disks were generally more likely to fragment. When the interaction timescale was significantly shorter than the disks' dynamical timescales, the proto-stellar disks tended to be truncated without forming objects. The newly-formed objects had masses ranging from 0.9 to 127 Jupiter masses, with the majority in the BD regime. They often resided in star-BD multiples and in some cases also formed hierarchical orbiting systems. Most of them had large angular momenta and highly flattened, disk-like shapes. The objects had radii ranging from 0.1 to 10 AU. The disk gas was assumed to be locally isothermal, appropriate for the short cooling times in extended proto-stellar disks, but not for condensed objects. An additional case with explicit cooling that reduced to zero for optically thick gas was simulated to test the extremes of cooling effectiveness and it was still possible to form objects in this case. Detailed radiative transfer is expected to lengthen the internal evolution timescale for these objects, but not to alter our basic results.

18 pages, 12 figures and 2 tables. Accepted for publication in MNRAS

References in corpus (8)

• The properties of brown dwarfs and low-mass hydrogen-burning stars formed by disc fragmentation
• Numerical requirements for simulations of self gravitating and non-self gravitating disks
• Inefficient star formation: The combined effects of magnetic fields and radiative feedback
• Secular evolution of viscous and self-gravitating circumstellar discs
• Multiplicity and Optical Excess Across the Substellar Boundary in Taurus
• Low Mass Stars and Brown Dwarfs in NGC 2024: Constraints on the Substellar Mass Function
• The GL 569 Multiple System
• The role of the energy equation in the fragmentation of protostellar discs during stellar encounters

Cited by in corpus (17)

• The stellar and sub-stellar IMF of simple and composite populations
• The Formation and Early Evolution of Low-mass Stars and Brown Dwarfs
• Tidally induced brown dwarf and planet formation in circumstellar discs
• Black Hole Binary Formation in AGN Discs: From Isolation to Merger
• The Jeans Mass as a Fundamental Measure of Self-Gravitating Disc Fragmentation and Initial Fragment Mass
• Convergence of the critical cooling rate for protoplanetary disk fragmentation achieved; the key role of numerical dissipation of angular momentum
• Particle hydrodynamics with tessellation techniques
• The enrichment history of cosmic metals
• The fragmentation of protostellar discs: the Hill criterion for spiral arms
• The IMF and multiplicity of stars from gravity, turbulence, magnetic fields, radiation and outflow feedback
• Stellar orbit evolution in close circumstellar disc encounters
• Substellar Objects in Nearby Young Clusters VII: The substellar mass function revisited
• Formation of freely floating sub-stellar objects via close encounters
• The Properties of Prestellar Discs in Isolated and Multiple Prestellar Systems
• Exciting spiral arms in protoplanetary discs from flybys
• Formation of free-floating planetary mass objects via circumstellar disk encounters
• The formation of planets by disc fragmentation