The Fragmentation of Magnetized, Massive Star-Forming Cores With Radiative Feedback

Myers, Andrew C.; McKee, Christopher F.; Cunningham, A. J.; Klein, Richard; Krumholz, Mark R.

doi:10.1088/0004-637x/766/2/97

Cited by 189 publications

(269 citation statements)

References 81 publications

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“…Indeed, we note that the relative unimportance of magnetic fields as opposed to radiation in preventing fragmentation on small scales around stars, as opposed to the formation of additional stars far from existing ones, is consistent with the findings of radiationmagnetohydrodynamic simulations (Commerçon, Hennebelle & Henning 2011;Myers et al 2013). These show that radiation rather than magnetic fields is more important in prevent fragmentation close to growing stars.…”

Section: Critical Massessupporting

confidence: 88%

“…Hansen et al (2012) and Krumholz, Klein & McKee (2012) included outflows with radiation, but not magnetic fields. The only published studies reporting radiation-magnetohydrodynamic simulations of the formation of multiple stars are those of Price & Bate (2009), Peters et al (2011), and Myers et al (2013. Only the last of these both includes protostellar outflows and, most importantly, forms enough stars that one can obtain meaningful statistics from it, albeit only in the mass range near the IMF peak that is best sampled.…”

Section: Introductionmentioning

confidence: 99%

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What physics determines the peak of the IMF? Insights from the structure of cores in radiation-magnetohydrodynamic simulations

Krumholz

Myers

Klein

et al. 2016

Mon. Not. R. Astron. Soc.

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As star-forming clouds collapse, the gas within them fragments to ever-smaller masses. Naively one might expect this process to continue down to the smallest mass that is able to radiate away its binding energy on a dynamical timescale, the opacity limit for fragmentation, at ∼ 0.01 M . However, the observed peak of the initial mass function (IMF) lies a factor of 20 − 30 higher in mass, suggesting that some other mechanism halts fragmentation before the opacity limit is reached. In this paper we analyse radiation-magnetohydrodynamic simulations of star cluster formation in typical Milky Way environments in order to determine what physical process limits fragmentation in them. We examine the regions in the vicinity of stars that form in the simulations to determine the amounts of mass that are prevented from fragmenting by thermal and magnetic pressure. We show that, on small scales, thermal pressure enhanced by stellar radiation heating is the dominant mechanism limiting the ability of the gas to further fragment. In the brown dwarf mass regime, ∼ 0.01 M , the typical object that forms in the simulations is surrounded by gas whose mass is several times its own that is unable to escape or fragment, and instead is likely to accrete. This mechanism explains why ∼ 0.01 M objects are rare: unless an outside agent intervenes (e.g., a shock strips away the gas around them), they will grow by accreting the warmed gas around them. In contrast, by the time stars grow to masses of ∼ 0.2 M , the mass of heated gas is only tens of percent of the central star mass, too small to alter its final mass by a large factor. This naturally explains why the IMF peak is at ∼ 0.2 M .

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Section: Critical Massessupporting

confidence: 88%

Section: Introductionmentioning

confidence: 99%

What physics determines the peak of the IMF? Insights from the structure of cores in radiation-magnetohydrodynamic simulations

Krumholz

Myers

Klein

et al. 2016

Mon. Not. R. Astron. Soc.

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“…The misalignment is expected if the angular momenta of dense cores are generated through turbulent motions (e.g., Burkert & Bodenheimer 2000;Seifried et al 2012b;Myers et al 2013;Joos et al 2013). Plausible observational evidence for it was recently uncovered by Hull et al (2013) using CARMA, who found that the distribution of the angle between the magnetic field on the 10 3 AU-scale and the bipolar outflow axis (taken as a proxy for the rotation axis) is consistent with being random.…”

Section: Magnetic Field-rotation Misalignmentmentioning

confidence: 97%

The Earliest Stages of Star and Planet Formation: Core Collapse, and the Formation of Disks and Outflows

Li¹,

Banerjee²,

Jørgensen³

et al. 2014

Protostars and Planets VI

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The formation of stars and planets are connected through disks. Our theoretical understanding of disk formation has undergone drastic changes in recent years, and we are on the brink of a revolution in disk observation enabled by ALMA. Large rotationally supported circumstellar disks, although common around more evolved young stellar objects, are rarely detected during the earliest, "Class 0" phase; a few excellent candidates have been discovered recently around both low-and high-mass protostars though. In this early phase, prominent outflows are ubiquitously observed; they are expected to be associated with at least small magnetized disks. Whether the paucity of large Keplerian disks is due to observational challenges or intrinsically different properties of the youngest disks is unclear. In this review we focus on the observations and theory of the formation of early disks and outflows, and their connections with the first phases of planet formation. Disk formation -once thought to be a simple consequence of the conservation of angular momentum during hydrodynamic core collapse -is far more subtle in magnetized gas. In this case, the rotation can be strongly magnetically braked. Indeed, both analytic arguments and numerical simulations have shown that disk formation is suppressed in the strict ideal magnetohydrodynamic (MHD) limit for the observed level of core magnetization. We review what is known about this "magnetic braking catastrophe", possible ways to resolve it, and the current status of early disk observations. Possible resolutions include non-ideal MHD effects (ambipolar diffusion, Ohmic dissipation and Hall effect), magnetic interchange instability in the inner part of protostellar accretion flow, turbulence, misalignment between the magnetic field and rotation axis, and depletion of the slowly rotating envelope by outflow stripping or accretion. Outflows are also intimately linked to disk formation; they are a natural product of magnetic fields and rotation and are important signposts of star formation. We review new developments on early outflow generation since PPV. The properties of early disks and outflows are a key component of planet formation in its early stages and we review these major connections.

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“…They found that rotationally supported disks (RSDs) do not form out of uniform and non-uniform cores under strong magnetic fields unless the field is misaligned with respect to the rotation axis (Hennebelle & Ciardi 2009). Turbulence has also been shown to help with disk formation (Santos-Lima et al 2012;Seifried et al 2012;Myers et al 2013;Joos et al 2013;Li et al 2014b).…”

Section: Introductionmentioning

confidence: 99%

Testing protostellar disk formation models with ALMA observations

Harsono

Dishoeck

Bruderer

et al. 2015

A&A

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Context. Recent simulations have explored different ways to form accretion disks around low-mass stars. However, it has been difficult to differentiate between the proposed mechanisms because of a lack of observable predictions from these numerical studies. Aims. We aim to present observables that can differentiate a rotationally supported disk from an infalling rotating envelope toward deeply embedded young stellar objects (M env > M disk ) and infer their masses and sizes. Methods. Two 3D magnetohydrodynamics (MHD) formation simulations are studied with a rotationally supported disk (RSD) forming in one but not the other (where a pseudo-disk is formed instead), together with the 2D semi-analytical model. We determine the dust temperature structure through continuum radiative transfer RADMC3D modeling. A simple temperature-dependent CO abundance structure is adopted and synthetic spectrally resolved submm rotational molecular lines up to J u = 10 are compared with existing data to provide predictions for future ALMA observations. Results. The 3D MHD simulations and 2D semi-analytical model predict similar compact components in continuum if observed at the spatial resolutions of 0.5-1 (70-140 AU) typical of the observations to date. A spatial resolution of ∼14 AU and high dynamic range (>1000) are required in order to differentiate between RSD and pseudo-disk formation scenarios in the continuum. The first moment maps of the molecular lines show a blue-to red-shifted velocity gradient along the major axis of the flattened structure in the case of RSD formation, as expected, whereas it is along the minor axis in the case of a pseudo-disk. The peak position-velocity diagrams indicate that the pseudo-disk shows a flatter velocity profile with radius than does an RSD. On larger scales, the CO isotopolog line profiles within large (>9 ) beams are similar and are narrower than the observed line widths of low-J (2-1 and 3-2) lines, indicating significant turbulence in the large-scale envelopes. However a forming RSD can provide the observed line widths of high-J (6-5, 9-8, and 10-9) lines. Thus, either RSDs are common or a higher level of turbulence (b ∼ 0.8 km s −1 ) is required in the inner envelope compared with the outer part (0.4 km s −1 ). Conclusions. Multiple spatially and spectrally resolved molecular line observations can differentiate between the pseudo-disk and the RSD much better than continuum data. The continuum data give a better estimate of disk masses, whereas the disk sizes can be estimated from the spatially resolved molecular lines observations. The general observable trends are similar between the 2D semi-analytical models and 3D MHD RSD simulations.

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The Fragmentation of Magnetized, Massive Star-Forming Cores With Radiative Feedback

Cited by 189 publications

References 81 publications

What physics determines the peak of the IMF? Insights from the structure of cores in radiation-magnetohydrodynamic simulations

What physics determines the peak of the IMF? Insights from the structure of cores in radiation-magnetohydrodynamic simulations

The Earliest Stages of Star and Planet Formation: Core Collapse, and the Formation of Disks and Outflows

Testing protostellar disk formation models with ALMA observations

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