Magnetic processes in a collapsing dense core I. Accretion and ejection

By P. Hennebelle, Sébastien Fromang. 2007

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Context. To understand the star formation process, it is important to study the collapse of a prestellar dense core. Aims. We investigate the effect of the magnetic field during the first collapse up to the formation of the first core, focusing particularly on the magnetic braking and the launching of outflows. Methods. We perform 3D AMR high resolution numerical simulations of a magnetically supercritical collapsing dense core using the RAMSES MHD code and develop semi-analytical models that we compare with the numerical results. Results. We study in detail the various profiles within the envelope of the collapsing core for various magnetic field strengths. Even modest values of magnetic field strength modify the collapse significantly. This is largely due to the amplification of the radial and toroidal components of the magnetic field by the differential motions within the collapsing core. For a weak magnetic intensity corresponding to an initial mass-to-flux over critical mass-to-flux ratio, μ equals 20 a centrifugally supported disk forms. The strong differential rotation triggers the growth of a slowly expanding magnetic tower. For higher magnetic field strengths corresponding to μ = 2, the collapse occurs primarily along the field lines, therefore delivering weaker angular momentum into the inner part whereas at the same time, strong magnetic braking occurs. As a consequence no centrifugally supported disk forms. An outflow is launched from the central thermally supported core. Detailed comparisons with existing analytical predictions indicate that it is magneto-centrifugally driven. Conclusions. For cores having a mass-to-flux over critical mass-to-flux radio μ < 5, the magnetic field appears to have a significant impact. The collapsing envelope is denser and flatter than in the hydrodynamical case and no centrifugally supported disk forms. For values μ < 20, the magnetic field drastically modifies the disk evolution. In a companion paper, the influence of the magnetic field on the dense core fragmentation is studied.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/adc90b44ac3dbfb9346d3c27a47f871e02d775bb

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Citations in the corpus

Disk formation during collapse of magnetized protostellar cores (2009, background): “2006) which transports angular momentum from the inner parts of the cloud towards its outer regions (Allen et al. 2003, Fromang et al. 2006, Price & Bate 2007, Hennebelle & Fromang 2008 (hereafter HF08), Mellon & Li 2008, 2009).”
Effect of Magnetic Braking on Circumstellar Disk Formation in a Strongly Magnetized Cloud (2010, result): “This type of outflow was seen in many previous studies (e.g., Tomisaka 2002; Machida et al. 2004, 2005b; Machida et al. 2006, 2008b; Hennebelle & Fromang 2008; Duffin & Pudritz 2009; Tomida et al. 2010).”
ANALYTICAL THEORY FOR THE INITIAL MASS FUNCTION. II. PROPERTIES OF THE FLOW (2009, background): “…magnetic field, which has been shown to severely inhibit disk fragmentation (Machida et al. 2005, 2008, Hennebelle & Teyssier 2008, Price & Bate 2008) or even to prevent disk formation by magnetic braking (Galli et al. 2006, Price & Bate 2007, Hennebelle & Fromang 2008, Mellon & Li 2008a,b).”
Magnetic Fields of Nondegenerate Stars (2009, methodology): “…clouds havinglar er initial magnetic fluxes forming in average first/second cores rotating slower and being more often single (e.g., Machida et al. 2008b; Hennebelle & Fromang 2008; Hennebelle & Teyssier 2008); it is however unclear yet how much of this can be extrapolated to more massive stars.”
On the diversity and statistical properties of protostellar discs (2018, background): “…core is aligned with a global field that is anchored at large distances from the centre of the core (Allen et al. 2003; Galli et al. 2006; Price & Bate 2007; Mellon & Li 2008; Hennebelle & Fromang 2008; Duffin & Pudritz 2009; Dapp & Basu 2010; Machida et al. 2011; Li et al. 2011; Dapp et al. 2012).”
NON-IDEAL MHD EFFECTS AND MAGNETIC BRAKING CATASTROPHE IN PROTOSTELLAR DISK FORMATION (2011, methodology): “This magnetic braking catastrophe was confirmed numerically by Mellon & Li (2008) and Hennebelle & Fromang (2008) using, respectively, 2D and 3D simulations (see also Price & Bate 2007), at least when the magnetic and rotation axes are aligned (see, however, Machida et al. 2010 and discussion in…”
THE GENERATION OF STRONG MAGNETIC FIELDS DURING THE FORMATION OF THE FIRST STARS (2010, background): “In particular, r ecent advances in the modeling of galactic star-forming clouds imply that the presence of magnetic fiel ds can reduce the level of fragmentation [20], and by doing so strongly influences the stellar mas s spectrum.”
Physical Processes in the Interstellar Medium (2014, background): “It can alter how cores fragment (Price and Bate 2007b, 2008; Hennebelle and Fromang 2008; Hennebelle and Teyssier 2008; Hennebelle et al. 2011; Peters et al. 2011), change the coupling”
LIMITING ACCRETION ONTO MASSIVE STARS BY FRAGMENTATION-INDUCED STARVATION (2010, background): “This objection is, however, weakened by the fact that magnetic fields are able to reduce the level of fragmentation on scales of molecular clouds as a whole (Heitsch et al. 2001) as well as of collapsing cloud cores (Hennebelle & Fromang 2008; Hennebelle & Teyssier 2008).”
The importance of radiative feedback for the stellar initial mass function (2008, background): “Recently, Price & Bate (2007) showed that stronger magnetic fields generally inhibit disc formation and binary formation (see also Hennebelle & Fromang 2008; Hennebelle & Teyssier 2008).”
OUTFLOW FEEDBACK REGULATED MASSIVE STAR FORMATION IN PARSEC-SCALE CLUSTER-FORMING CLUMPS (2009, background): “Magnetic braking driven bubbles provide a form of energy feedback that should accompany any star formed in a magnetized cloud (e.g., Draine 1980; Tomisaka 1998; Banerjee & Pudritz 2006; Mellon & Li 2008; Hennebelle & Fromang 2008) but is absent from purely hydrodynamic models.”
Small-scale dynamo action during the formation of the first stars and galaxies - I. The ideal MHD limit (2010, background): “…numerical studies of the collapse of magnetised molecular cloud cores in the context of present-day star formation (e.g. Hennebelle & Teyssier 2008; Hennebelle & Fromang 2008; Hennebelle & Ciardi 2009; Mellon & Li 2009) indicate that even modest field strengths can suppress binary formation and…”
Ambipolar diffusion in low-mass star formation - I. General comparison with the ideal magnetohydrodynamic case (2015, background): “…result of the very effective magnetic braking created by a strong pile-up of magnetic flux towards the centre of the collapsing system (Galli et al. 2006, Allen et al. 2003, Price & Bate 2007; Hennebelle & Teyssier 2008; Matsumoto & Tomisaka 2004; Hennebelle & Fromang 2008; Commerçon et al. 2010).”
Protostellar disk formation and transport of angular momentum during magnetized core collapse (2012, methodology): “5 − 10, Mellon & Li 2008; Price & Bate 2007; Hennebelle & Fromang 2008).”
Stellar, brown dwarf and multiple star properties from hydrodynamical simulations of star cluster formation (2008, background): “Recently, Price & Bate (2007) showed that stronger magnetic fields generally inhibit disc formation and binary formation (see also Hennebelle & Fromang 2008; Hennebelle & Teyssier 2008).”
H II REGIONS: WITNESSES TO MASSIVE STAR FORMATION (2010, background): “Banerjee & Pudritz (2006), Machida et al. (2005), Hennebelle & Teyssier (2008), Hennebelle & Fromang (2008) and Hennebelle & Ciardi (2009) furthermore show that the presence of magnetic fields can dramatically alter the shape and size of accretion disks and strongly suppress the formation of close…”
Our astrochemical heritage (2012, background): “…simulations of collapsing cores (e.g., Allen 4IMHD assumes that the mass to magnetic-flux ratio is constant, which implies that magnetic field lines follow the gas motions, i.e. the magnetic field is “frozen” into the neutral medium. et al. 2003; Mellon and Li 2008; Hennebelle and Fromang 2008).”