The Formation of Brown Dwarfs as Ejected Stellar Embryos

By B. Reipurth, C. Clarke. 2001

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We conjecture that brown dwarfs are substellar objects because they have been ejected from small newborn multiple systems that have decayed in dynamical interactions. In this view, brown dwarfs are stellar embryos for which the star formation process was aborted before the hydrostatic cores could build up enough mass to eventually start hydrogen burning. The disintegration of a small multiple system is a stochastic process, which can be described only in terms of the half-life of the decay. A stellar embryo competes with its siblings in order to accrete infalling matter, and the one that grows slowest is most likely to be ejected. With better luck, a brown dwarf would therefore have become a normal star. This interpretation of brown dwarfs readily explains the rarity of brown dwarfs as close companions to normal stars, the absence of wide brown dwarf binaries, and the flattening of the low-mass end of the initial mass function. Possible observational tests of this scenario include statistics of brown dwarfs near Class 0 sources and the kinematics of brown dwarfs in star-forming regions, while they still retain a kinematic signature of their expulsion. Because the ejection process limits the amount of gas brought along in a disk, it is predicted that substellar equivalents to the classical T Tauri stars should be rather short-lived.

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

The Gemini Deep Planet Survey (2007, result): “The competitive accretion and ejection mechanism that was proposed initially to explain the formation of BDs (Reipurth & Clarke 2001) could also form planetary mass companions on large orbits, as suggested by the results of recent simulations by Bate & Bonnell (2005).”
The formation of free-floating brown dwarves and planetary-mass objects by photo-erosion of prestellar cores (2004, unknown): “Reipurth & Clarke (2001) have suggested 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.…”
THE VLA NASCENT DISK AND MULTIPLICITY SURVEY OF PERSEUS PROTOSTARS (VANDAM). II. MULTIPLICITY OF PROTOSTARS IN THE PERSEUS MOLECULAR CLOUD (2016, background): “A promising route to explain these systems is a dynamical ejection scenario (Reipurth & Clarke 2001; Reipurth et al. 2010; Reipurth & Mikkola 2012).”
The properties of brown dwarfs and low-mass hydrogen-burning stars formed by disc fragmentation (2008, background): “As a consequence of ejection they stop accreting, and so they never acquire sufficient mass to sustain hydrogen burning (Reipurth & Clarke 2001).”
THE HAWAII INFRARED PARALLAX PROGRAM. II. YOUNG ULTRACOOL FIELD DWARFS (2016, background): “Two natural explanations are that some young objects experience early dynamical interactions that lead to significant acceleration (e.g., ejection from their birth clouds; Reipurth & Clarke 2001) or old (high-gravity) objects can display spectra that mimic low gravity.”
The primordial binary population. I. A near-infrared adaptive optics search for close visual companions to A star members of Scorpius OB2 (2004, unknown): “The presence of this gap could support the embryo-ejection formation scenario for brown dwarfs (e.g. Reipurth & Clarke 2001; Bate et al. 2003; Kroupa & Bouvier 2003).”
Brown dwarfs in the Pleiades cluster: Clues to the substellar mass function , (2002, background): “Reipurth & Clarke (2001) proposed that substellar objects are “stellar embryos” according to the following scenario: as molecular cloud cores fragment to form unstable protostellar multiple systems which decay dynamically, the lowest mass fragments are ejected from the core, and deprived of…”
On the diversity and statistical properties of protostellar discs (2018, background): “The observed small disc sizes would be consistent with brown dwarfs being ejected from multiple protostellar systems during their formation (Reipurth & Clarke 2001; Bate et al. 2002a; Goodwin & Whitworth 2007; Stamatellos et al. 2007; Bate 2009a, 2012).”
Evidence for a T Tauri Phase in Young Brown Dwarfs (2003, background): “A key prediction of Reipurth & Clarke (2001) is that " sub-stellar equivalents to the classical T Tauri stars should be rather short-lived " because the ejection process limits the amount of gas brought along in a disk.”
On the Evolutionary Status of Class I Stars and Herbig-Haro Energy Sources in Taurus-Auriga (2004, background): “The presence of circumstellar material and accretion argues against low-mass star/brown dwarf formation scenarios involving early ejection from a competitively accreting cluster (e.g., Reipurth & Clarke 2001).”
Very Low Mass Stars and Brown Dwarfs in Taurus-Auriga (2002, background): “The ejected core , removed from the reservoir of material , would grow from its low possibly substellar mass ( Reipurth & Clarke 2001 ) .”
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…”
Stellar, brown dwarf and multiple star properties from a radiation hydrodynamical simulation of star cluster formation (2011, background): “Reipurth & Clarke (2001) also speculated that if brown dwarfs formed via ejection, they might have smaller, lower-mass discs than stars.”
MAPPING THE SHORES OF THE BROWN DWARF DESERT. II. MULTIPLE STAR FORMATION IN TAURUS–AURIGA (2011, background): “The most popular formulation of this concept is the “embryo ejection” model of star formation (Reipurth & Clarke 2001), which postulates that protostellar cores produce many low-mass protostars or proto-brown dwarfs, but most are ejected from the protostellar envelope (and hence cut off from the…”
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, methodology): “We take the value of 3 km s 1 since this is the value calculated for the ejection velocity of, on average, more massive single objects from a dissolving minicluster (Sterzik & Durisen 1998; Reipurth & Clarke 2001).”
The formation mechanism of brown dwarfs (2002, methodology): “This latter mechanism is similar to that discussed by Reipurth & Clarke (2001).”
The stellar and sub-stellar IMF of simple and composite populations (2011, background): “This velocity dispersion can either be the same as that of the stars if BDs form like stars, or larger if they are ejected embryos (Reipurth & Clarke 2001).”