Collapse of Rotating Magnetized Molecular Cloud Cores and Mass Outflows

By Kohji Tomisaka. 2001

162 citations recorded by the source corpus.

The collapse of rotating magnetized molecular cloud cores is studied with axisymmetric magnetohydrodynamic (MHD) simulations. Because of the change of the equation of state of the interstellar gas, molecular cloud cores experience several phases during the collapse. In the earliest isothermal runaway collapse (n ≲ 1010 H2 cm-3), a pseudodisk is formed, and it continues to contract until an opaque core is formed at the center. In this disk, a number of MHD fast and slow shock pairs appear whose wave fronts are parallel to the disk. We assume that the interstellar gas obeys a polytropic equation of state with the exponent of Γ > 1 above the critical density at which the core becomes optically thick against the thermal radiation from dusts ncr ~ 1010 cm-3. After the equation of state becomes hard, an adiabatic quasi-static core forms at the center (the first core), which is separated from the isothermal contracting pseudodisk by the accretion shock front facing radially outward. By the effect of the magnetic tension, the angular momentum is transferred from the disk midplane to the surface. The gas with an excess angular momentum near the surface is finally ejected, which explains the molecular bipolar outflow. Two types of outflows are found. When the poloidal magnetic field is strong (its energy is comparable to the thermal one), a U-shaped outflow is formed, in which gas is mainly outflowing through a region whose shape looks like a capital letter U at a finite distance from the rotation axis. The gas is accelerated by the centrifugal force and the magnetic pressure gradient of the toroidal component. The other is a turbulent outflow in which magnetic field lines and velocity fields seem to be randomly oriented. In this case, globally the gas moves out almost perpendicularly from the disk, and the outflow looks like a capital letter I. In this case, although the gas is launched by the centrifugal force, the magnetic force working along the poloidal field lines plays an important role in expanding the outflow. The continuous mass accretion leads to a quasi-static contraction of the first core. A second collapse due to the dissociation of H2 occurs in it. Finally, another less massive quasi-static core is formed by atomic hydrogen (the second core). At the same time, it is found that another outflow is ejected around the second atomic core, which seems to correspond to the optical jets or the fast neutral winds.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/969cffd42272147145bd690571709d572192f4c2

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Citations in the corpus

High- and Low-Velocity Magnetized Outflows in the Star Formation Process in a Gravitationally Collapsing Cloud (2008, methodology): “…1998, 2000, 2002;Burkert&Balsara 2001;Matsumoto & Tomisaka 2004; Machida et al. 2004, 2005a; Fromang et al. 2006;Banerjee&Pudritz 2006;Hennebelle&Fromang 2008) and that the high-velocity flow is driven from another core (Tomisaka 2002; Banerjee & Pudritz 2006; Machida et al. 2006a, 2007a).”
Collapse of Magnetized Singular Isothermal Toroids. II. Rotation and Magnetic Braking (2003, background): “Rotation decreases somewhat the rate of mass accretion onto the central point mass, a trend also present in the calculations of Tomisaka (2002) and Krasnopolsky & Königl (2002).”
Outflows and Jets from Collapsing Magnetized Cloud Cores (2005, methodology): “Such large scale, low velocity outflows are also seen in other collapse simulations (e.g., Tomisaka 1998, 2002; Allen et al. 2003).”
Gravitational Collapse of Magnetized Clouds. I. Ideal Magnetohydrodynamic Accretion Flow (2006, background): “…calculations and numerical simulations have extended these works to follow the increase of density towards the formation of an optically thick core (Tomisaka 2002, Machida et al. 2005a,b) and through the formation of a point-mass into the protostellar accretion phase (Li & Shu 1997; Ciolek &…”
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).”
RADIATION MAGNETOHYDRODYNAMIC SIMULATIONS OF PROTOSTELLAR COLLAPSE: NONIDEAL MAGNETOHYDRODYNAMIC EFFECTS AND EARLY FORMATION OF CIRCUMSTELLAR DISKS (2015, background): “…are strong enough to remove angular momenta efficiently and overcome the centrifugal barrier (Basu & Mouschovias 1994, 1995a, 1995b; Mouschovias & Paleologou 1979, 1980; Tomisaka 1998, 2000, 2002; Machida et al. 2005a, 2005b, 2011a; Commerçon et al. 2010; Tomida et al. 2010b; Bate et al. 2014).”
The physics of star formation (2003, background): “It seems almost certain that both rotation and magnetic fields are involved in the origin of the bipolar outflows, although the various models that have been proposed differ considerably in their details (Königl and Ruden 1993: Königl and Pudritz 2000; Shu et al 2000; Tomisaka 2002).”
The Burst Mode of Protostellar Accretion (2006, background): “…the full effect of magnetic fields, since there is expected to be significant magnetic braking (Krasnopolsky & Königl 2002), collapse-driven outflow (Tomisaka 2002), and magnetorotational instability (Fromang et al. 2005), all of which can play a role in the angular momentum evolution of the disk.”
RADIATION MAGNETOHYDRODYNAMIC SIMULATIONS OF PROTOSTELLAR COLLAPSE: PROTOSTELLAR CORE FORMATION (2012, background): “On the other hand, Tomisaka (1998, 2000, 2002) showed that magnetic fields transport angular momentum far more efficiently via torsional Alfvén waves (so-called magnetic braking; Mouschovias & Paleologou 1979, 1980) and bipolar outflows using two-dimensional (2D) MHD simulations.”
THE INTERPLAY OF MAGNETIC FIELDS, FRAGMENTATION, AND IONIZATION FEEDBACK IN HIGH-MASS STAR FORMATION (2010, background): “…with viable suggestions including disk winds (Blandford & Payne 1982; Königl & Pudritz 2000), tower flows produced by wound up toroidal field (Tomisaka 1998, 2002; Matsumoto & Tomisaka 2004; Machida et al. 2004; Banerjee & Pudritz 2006, 2007) or interactions between the disk field and…”
Theory of Star Formation (2007, background): “A prediction of these simulations is that a slow (v ∼ cs ∼ 0.2 km s−1) outflow should occur at large radii (∼ 103 AU; Tomisaka, 1998, 2002; Banerjee & Pudritz, 2006).”