The formation mechanism of brown dwarfs

By Matthew R. Bate, Ian A. Bonnell, Volker Bromm. 2002

301 citations recorded by the source corpus.

We present results from the first hydrodynamical star formation calculation to demonstrate that brown dwarfs are a natural and frequent product of the collapse and fragmentation of a turbulent molecular cloud. The brown dwarfs form via the fragmentation of dense molecular gas in unstable multiple systems and are ejected from the dense gas before they have been able to accrete to stellar masses. Thus, they can be viewed as 'failed stars'. Approximately three-quarters of the brown dwarfs form in gravitationally unstable circumstellar discs while the remainder form in collapsing filaments of molecular gas. These formation mechanisms are very efficient, producing roughly the same number of brown dwarfs as stars, in agreement with recent observations. However, because close dynamical interactions are involved in their formation, we find a very low frequency of binary brown dwarf systems (≤5 per cent) and that those binary brown dwarf systems that do exist must be close, ≤ 10 au. Similarly, we find that young brown dwarfs with large circumstellar discs (radii ≥ 10 au) are rare ( 5 per cent).

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/bcdf63fd76991454b08160b37f1f50c112cb6341

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

Citations in the corpus

Detection of Nine M8.0-L0.5 Binaries: The Very Low Mass Binary Population and Its Implications for Brown Dwarf and Very Low Mass Star Formation (2003, background): “Assuming (as has been suggested by Reid et al. 2002; Bate et al. 2002) that eventually a close multiple encounter ejects VLM (<0.185M ) binaries, it would be interesting to see if such an ‘‘ ejected ’’ VLM binary distribution would have a maximum separation of 16 AU as observed.”
Imaging Extrasolar Giant Planets (2016, background): “…burning limit (≈75 MJup) to brown dwarfs at the opacity limit for fragmenta- 23 tion (≈5–10 MJup), which corresponds to the minimum mass of a pressure-supported fragment during the collapse of a molecular cloud core (Low & Lynden-Bell 1976; Silk 1977; Boss 2001; Bate et al. 2002; Bate 2009).”
New Brown Dwarfs and an Updated Initial Mass Function in Taurus (2004, background): “For instance, Reipurth & Clarke (2001), Boss (2001), and Bate et al. (2002) have suggested that brown dwarfs could form as protostellar sources whose accretion is prematurely halted by ejection from multiple systems.”
Simulating star formation in molecular cloud cores. I. The influence of low levels of turbulence on fragmentation and multiplicity (2003, background): “Dynamical interactions and ejections have been proposed by Reipurth & Clarke (2001) (see also Bate et al. 2002a, Delgardo-Donate et al. 2003) as a mechanism for the production of brown dwarves: stellar embryos are ejected from cores before they can accrete enough material to become hydrogenburning…”
Measuring Accretion in Young Substellar Objects: Approaching the Planetary Mass Regime (2005, background): “…brown dwarfs form from the collapse of very low mass cloud cores, such as those produced by turbulent fragmentation (Padoan & Nordlund 2002), or whether they are created via ejecion of low-mass embryos from the main reservoirs of gas in a molecular cloud (Reipurth & Clarke 2001; Bate et al. 2002).”
The formation of close binary systems by dynamical interactions and orbital decay (2002, background): “The formation mechanism of the brown dwarfs in this calculation has been discussed by Bate et al. (2002a).”
Accretion in stellar clusters and the collisional formation of massive stars (2002, background): “This extends a similar finding that gas accretion on its own is capable of explaining the IMF (Bonnell et al. 2001b).”
The Stellar Population of the Chamaeleon I Star-forming Region (2007, background): “Several studies have suggested that brown dwarfs form by the ejection of protostellar sources from multiple systems (Reipurth & Clarke 2001; Boss 2001; Bate et al. 2002; Delgado-Donate, Clarke, & Bate 2003; Umbreit et al. 2005; Goodwin & Whitworth 2007).”
THE PALOMAR/KECK ADAPTIVE OPTICS SURVEY OF YOUNG SOLAR ANALOGS: EVIDENCE FOR A UNIVERSAL COMPANION MASS FUNCTION (2008, methodology): “Based on results from three-dimensional smoothed particle hydrodynamic simulations, Bate et al. (2002) and Bate & Bonnell (2005) estimate that the opacity limit for gravo-turbulent fragmentation may be as low as 3–10 MJup.”
The formation of free-floating brown dwarves and planetary-mass objects by photo-erosion of prestellar cores (2004, methodology): “…that this is because brown dwarves are ejected from nascent multiple systems before they can acquire sufficient mass to become Main Sequence stars, and this suggestion is supported by the numerical simulations of Bate et al. (2002), Delgado Donate et al. (2003) and Goodwin et al. (2004a,b).”
The origin of the initial mass function and its dependence on the mean Jeans mass in molecular clouds (2004, methodology): “In thissection,we investigate in detailwhy the second calculation form sm ore brown dwarfsthan the rst.From Calculation 1,Bate et al.(2002a) found that the m echanism forbrown dwarfform ation wasthata fragm entwasejected from the region ofdense m olecular gas in which it form ed c 0000 R A S,M N R…”
The First Stars (2003, background): “A fraction of the accreting cores is ejected, by slingshot interactions with neighboring ones, from the natal cloud before they could grow to stellar masses, and thus end up as brown dwarfs (Bate et al. 2002).”
Global hierarchical collapse in molecular clouds. Towards a comprehensive scenario (2019, background): “Numerical simulations including this so-called opacitylimited fragmentation also show an efficient formation of brown dwarfs (Bate et al. 2002), and in fact the problem then becomes to avoid an excessive formation of these objects by inclusion of radiative transfer to adequately model the gas…”
The effect of magnetic fields on star cluster formation (2008, background): “Thus, low mass stars are simply those which have been quickly ejected from multiple systems and thus have only a short accretion history (Bate et al. 2002; Bate & Bonnell 2005), whereas higher mass stars are those which form and remain at the bottom f deep potential wells and build up their mass…”
LOW VIRIAL PARAMETERS IN MOLECULAR CLOUDS: IMPLICATIONS FOR HIGH-MASS STAR FORMATION AND MAGNETIC FIELDS (2013, background): “…observations constrain under which conditions numerical cloud simulations with initial virial parameters α > 1 (e.g., series of simulations started by Bate et al. 2002) or α < 1 (e.g., Hennebelle et al. 2011) may apply, and why some stellar clusters might be born with velocity dispersions too low…”