The formation of binary and multiple star systems

Chapman, Sydney; Pongracic, H.; Disney, M. J.; Nelson, A. H.; Turner, J. A.; Whitworth, Anthony Peter

doi:10.1038/359207a0

Cited by 54 publications

(48 citation statements)

References 19 publications

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“…A mechanism which drives mass ratios towards unity in simulations of star formation was first described by Chapman et al (1992), and has subsequently been noted by Burkert & Bodenheimer (1993) and by Bate & Bonnell (1997) (but see Ochi et al 2005 for a different view, and Clarke 2007, for a rebuttal of Ochi et al). If a binary system continues to grow by accretion, the specific angular momentum of the infalling material (relative to the centre of mass of the binary system) tends to increase with time.…”

Section: Multiplicitymentioning

confidence: 99%

Simulating star formation in molecular cloud cores

Attwood

Goodwin²,

Stamatellos

et al. 2009

A&A

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Context. Observations suggest that low-mass stars condense out of dense, relatively isolated, molecular cloud cores, with each core spawning a small-N cluster of stars. Aims. Our aim is to identify the physical processes shaping the collapse and fragmentation of a 5.4 M core, and to understand how these processes influence the mass distribution, kinematics, and binary statistics of the resulting stars. Methods. We perform SPH simulations of the collapse and fragmentation of cores having different initial levels of turbulence (α TURB = 0.05, 0.10, 0.25). We use a new treatment of the energy equation that captures (i) excitation of the rotational and vibrational degrees of freedom of H 2 , dissociation of H 2 , ionisation of H and He; and (ii) the transport of cooling radiation against opacity due to both dust and gas (including the effects of dust sublimation, molecules, and H − ions). We also perform comparison simulations using a standard barotropic equation of state. Results. We find that -when compared with the barotropic equation of state -our more realistic treatment of the energy equation results in more protostellar objects being formed, and a higher proportion of brown dwarfs; the multiplicity frequency is essentially unchanged, but the multiple systems tend to have shorter periods (by a factor ∼3), higher eccentricities, and higher mass ratios. The reason for this is that small fragments are able to cool more effectively with the new treatment, as compared with the barotropic equation of state. We also note that in our simulations the process of fragmentation is often bimodal, in the following sense. The first protostar to form is usually, at the end, the most massive, i.e. the primary. However, frequently a disc-like structure subsequently forms round this primary, and then, once it has accumulated sufficient mass, quickly fragments to produce several secondaries. Conclusions. We believe that this delayed fragmentation of a disc-like structure is likely to be an important source of very low-mass stars in nature (both low-mass hydrogen-burning stars and brown dwarf stars); hence it may be fundamental to understanding the way in which the statistical properties of stars change -continuously but monotonically -with decreasing mass. However, in our simulations the individual cores probably produce too many stars, and hence too many single stars. We list the physical and numerical features that still need to be included in our simulations to make them more realistic; in particular, radiative and mechanical feedback, non-ideal magneto-hydrodynamic effects, and a more sophisticated implementation of sink particles.

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Section: Multiplicitymentioning

confidence: 99%

Simulating star formation in molecular cloud cores

Attwood

Goodwin²,

Stamatellos

et al. 2009

A&A

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“…However, it is difficult to evaluate the contribution that collisions make to the overall galactic star formation rate, as we do not know how frequently such collisions occur, nor how star formation proceeds when they do (e.g Pongracic et al 1992;Chapman et al 1992;Whitworth et al 1994;Heitsch et al 2006;Inoue & Fukui 2013;Dobbs, Pringle & Duarte-Cabral 2015). Moreover, instances where on-going star formation may have been triggered by cloud-cloud collisions are hard to identify, and the observations are difficult to interpret unambiguously (Haworth et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Star formation triggered by cloud–cloud collisions

Balfour

Whitworth

Hubber

et al. 2015

Mon. Not. R. Astron. Soc.

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We present the results of SPH simulations in which two clouds, each having mass M O = 500 M and radius R O = 2 pc, collide head-on at relative velocities of ∆v O = 2.4, 2.8, 3.2, 3.6 and 4.0 km s −1 . There is a clear trend with increasing ∆v O . At low ∆v O , star formation starts later, and the shock-compressed layer breaks up into an array of predominantly radial filaments; stars condense out of these filaments and fall, together with residual gas, towards the centre of the layer, to form a single large-N cluster, which then evolves by competitive accretion, producing one or two very massive protostars and a diaspora of ejected (mainly low-mass) protostars; the pattern of filaments is reminiscent of the hub and spokes systems identified recently by observers. At high ∆v O , star formation occurs sooner and the shock-compressed layer breaks up into a network of filaments; the pattern of filaments here is more like a spider's web, with several small-N clusters forming independently of one another, in cores at the intersections of filaments, and since each core only spawns a small number of protostars, there are fewer ejections of protostars. As the relative velocity is increased, the mean protostellar mass increases, but the maximum protostellar mass and the width of the mass function both decrease. We use a Minimal Spanning Tree to analyse the spatial distributions of protostars formed at different relative velocities.

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“…If star formation is dynamically-triggered, then the stars formed will be much more tightly clustered than is the average across the whole of the star-forming region. For instance, in simulations of star formation triggered by clump-clump collisions in a GMC (Chapman et al 1992, the majority of the stars that are formed undergo encounters. The star formation in such events is coeval, however, so that the initial encounters that occur are likely to be disc-disc rather than disc-star interactions.…”

Section: Capture Ratesmentioning

confidence: 99%

Numerical simulations of protostellar encounters - I. Star-disc encounters

Boffin¹,

Watkins²,

Bhattal³

et al. 1998

Monthly Notices RAS

101

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It appears that most stars are born in clusters, and that at birth most stars have circumstellar discs which are comparable in size to the separations between the stars. Interactions between neighbouring stars and discs are therefore likely to play a key rôle in determining disc lifetimes, stellar masses, and the separations and eccentricities of binary orbits. Such interactions may also cause fragmentation of the discs, thereby triggering the formation of additional stars.We have carried out a series of simulations of disc-star interactions using an SPH code which treats self-gravity, hydrodynamic and viscous forces. We find that interactions between discs and stars provide a mechanism for removing energy from, or adding energy to, the orbits of the stars, and for truncating the discs. However, capture during such encounters is unlikely to be an important binary formation mechanism.A more significant consequence of such encounters is that they can trigger fragmentation of the disc, via tidally and compressionally induced gravitational instabilities, leading to the formation of additional stars. When the disc-spins and stellar orbits are randomly oriented, encounters lead to the formation of new companions to the original star in 20% of encounters. If most encounters are prograde and coplanar, as suggested by simulations of dynamically-triggered star formation, then new companions are formed in approximately 50% of encounters.

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The formation of binary and multiple star systems

Cited by 54 publications

References 19 publications

Simulating star formation in molecular cloud cores

Simulating star formation in molecular cloud cores

Star formation triggered by cloud–cloud collisions

Numerical simulations of protostellar encounters - I. Star-disc encounters

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