The “Mysterious” Origin of Brown Dwarfs

By P. Padoan, Åke Nordlund. 2002

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Hundreds of brown dwarfs (BDs) have been discovered in the last few years in stellar clusters and among field stars. BDs are almost as numerous as hydrogen-burning stars, and so a theory of star formation should also explain their origin. The "mystery" of the origin of BDs is that their mass is 2 orders of magnitude smaller than the average Jeans mass in star-forming clouds, and yet they are so common. In this work we investigate the possibility that gravitationally unstable protostellar cores of BD mass are formed directly by the process of turbulent fragmentation. Supersonic turbulence in molecular clouds generates a complex density field with a very large density contrast. As a result, a fraction of BD mass cores formed by the turbulent flow are dense enough to be gravitationally unstable. We find that with density, temperature, and rms Mach number typical of cluster-forming regions, turbulent fragmentation can account for the observed BD abundance.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/b8efa8ad0b125086d762ac55afc977eb030ab973

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Citations in the corpus

The T Tauri Phase Down to Nearly Planetary Masses: Echelle Spectra of 82 Very Low Mass Stars and Brown Dwarfs (2005, background): “Some theorists, most recently Padoan & Nordlund (2004), have suggested that objects all the way from solar-mass stars to brown dwarfs form the same way, via ‘‘turbulent fragmentation.’’”
THE STAR FORMATION RATE OF SUPERSONIC MAGNETOHYDRODYNAMIC TURBULENCE (2009, methodology): “In Padoan & Nordlund (2004) we computed the mass fraction available to form brown dwarfs as the integral of the pdf of gas density from a critical density to infinity.”
AB INITIO EQUATIONS OF STATE FOR HYDROGEN (H-REOS.3) AND HELIUM (He-REOS.3) AND THEIR IMPLICATIONS FOR THE INTERIOR OF BROWN DWARFS (2014, result): “Since there is an overlapping mass regime of BDs and GPs (Hennebelle & Chabrier 2008; Padoan & Nordlund 2004), we also assume that the GP KOI-889b consists of a homogeneous layer, in contrast to the three layer model applied for Jupiter, see the previous section.”
THE VLA NASCENT DISK AND MULTIPLICITY SURVEY OF PERSEUS PROTOSTARS (VANDAM). II. MULTIPLICITY OF PROTOSTARS IN THE PERSEUS MOLECULAR CLOUD (2016, background): “…thermal (Jeans) fragmentation aided by rotation and asymmetry (e.g., Bonnell & Bastien 1993; Burkert & Bodenheimer 1993) or turbulent fragmentation (Padoan & Nordlund 2002, 2004; Offner et al. 2010); these routes tend to produce companions on ∼1000 au scales, but can also result in companions with…”
Gravoturbulent Formation of Planetesimals (2005, methodology): “This process is very similar to the gravoturbulent fragmentation of molecular clouds into protostellar cores (Klessen et al. 2000; Padoan & Nordlund 2004).”
Theory of Star Formation (2007, background): “A recent comprehensive proposal to explain the CMF and IMF has been advanced by Padoan & Nordlund (2002, 2004) (hereafter “PN”).”
The properties of brown dwarfs and low-mass hydrogen-burning stars formed by disc fragmentation (2008, background): “Padoan & Nordlund (2004) suggest that magnetoturbulent fragmentation of molecular clouds produces prestellar cores of brown-dwarf mass with densities high enough for them to be gravitationally unstable and collapse.”
Gravitational fragmentation and the formation of brown dwarfs in stellar clusters (2008, background): “Turbulent fragmentation (Padoan & Nordlund 2002) envisions that strong, magnetic shocks produce high density post-shock gas which will have low Jeans masses and therefore form brown dwarfs directly from the turbulence ⋆ E-mail: iab1@st-and.ac.uk (Padoan & Nordlund 2004).”
The stellar and sub-stellar IMF of simple and composite populations (2011, background): “…in a dissipating turbulent interstellar medium (Nordlund & Padoan 2003; Padoan & Nordlund 2002; Mac Low & Klessen 2004; Tilley & Pudritz 2004; Padoan & Nordlund 2004; Hennebelle & Chabrier 2008, 2009; Elmegreen 2011) augmented with massdependent accretion and accretion-truncation…”
The Formation and Early Evolution of Low-Mass Stars and Brown Dwarfs (2012, background): “Turbulent compression and fragmentation of gas in a molecular cloud produces collapsing cores over a wide range of masses (Elmegreen 2011, Hennebelle & Chabrier 2008, Padoan & Nordlund 2002, 2004).”