THE BURST MODE OF ACCRETION AND DISK FRAGMENTATION IN THE EARLY EMBEDDED STAGES OF STAR FORMATION

By Eduard I. Vorobyov, S. Basu. 2010

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We revisit our original papers on the burst mode of accretion by incorporating a detailed energy balance equation into a thin-disk model for the formation and evolution of circumstellar disks around low-mass protostars. Our model includes the effect of radiative cooling, viscous and shock heating, and heating due to stellar and background irradiation. Following the collapse from the prestellar phase allows us to model the early embedded phase of disk formation and evolution. During this time, the disk is susceptible to fragmentation, depending upon the properties of the initial prestellar core. Globally, we find that higher initial core angular momentum and mass content favors more fragmentation, but higher levels of background radiation can moderate the tendency to fragment. A higher rate of mass infall onto the disk than that onto the star is a necessary but not a sufficient condition for disk fragmentation. More locally, both the Toomre Q-parameter needs to be below a critical value and the local cooling time needs to be shorter than a few times the local dynamical time. Fragments that form during the early embedded phase tend to be driven into the inner disk regions and likely trigger mass accretion and luminosity bursts that are similar in magnitude to FU-Orionis-type or EX-Lupi-like events. Disk accretion is shown to be an intrinsically variable process, thanks to disk fragmentation, nonaxisymmetric structure, and the effect of gravitational torques. The additional effect of a generic α-type viscosity acts to reduce burst frequency and accretion variability, and is likely to not be viable for values of α significantly greater than 0.01.

Subfields: Astronomy and Astrophysics, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/b5b91bd47db83a3b548ef474e1e463d09a742d7d

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Citations in the corpus

Protoplanetary Disks and Their Evolution (2011, background): “The instabilities would lead to sporadic bursts of high accretion (Zhu et al. 2009) and prevent the disk mass from growing faster than the star (Vorobyov & Basu 2010).”
THREE-DIMENSIONAL SIMULATION OF MASSIVE STAR FORMATION IN THE DISK ACCRETION SCENARIO (2011, background): “…et al. 1992; Tomley et al. 1994; Laughlin & Bodenheimer 1994; Miyama et al. 1994; Papaloizou & Lin 1995a; Laughlin & Korchagin 1996; Laughlin & Rozyczka 1996; Bate 1998; Yorke & Bodenheimer 1999; Vorobyov & Basu 2006, 2007, 2010) in the accretion disk will transfer angular momentum to outer radii.”
RADIATION MAGNETOHYDRODYNAMIC SIMULATIONS OF PROTOSTELLAR COLLAPSE: NONIDEAL MAGNETOHYDRODYNAMIC EFFECTS AND EARLY FORMATION OF CIRCUMSTELLAR DISKS (2015, background): “While mass and angular momentum transport by magnetic fields are almost steady and smooth, the gravitational torque via nonaxisymmetric structures is unsteady and episodic (see also Vorobyov & Basu 2006, 2010; Stamatellos et al. 2011).”
Accretion onto Pre-Main-Sequence Stars (2016, background): “…could be explained by highly time-variable accretion, where much of the mass was accreted in short bursts like those of FU Ori objects (Section 2.5), so that most protostars are observed in a low-accretion, low-luminosity state (see also Vorobyov & Basu 2005, 2010, 2015, Bae et al. 2013, 2014).”
VARIABLE PROTOSTELLAR ACCRETION WITH EPISODIC BURSTS (2015, methodology): “Systems with ξ & 0.1 are likely to be unstable to fragmentation (Vorobyov & Basu 2010a).”
Rapid inward migration of planets formed by gravitational instability (2011, background): “…have observed that clumps could drift inwards (e.g., Mayer et al. 2002; Boss 2005; Cha & Nayakshin 2010), and some of them have focused on the early phases of disc formation and evolution following the collapse from the prestellar core stage (Vorobyov & Basu 2006, 2010a,b; Machida et al. 2011).”
THE VLA NASCENT DISK AND MULTIPLICITY SURVEY OF PERSEUS PROTOSTARS (VANDAM). II. MULTIPLICITY OF PROTOSTARS IN THE PERSEUS MOLECULAR CLOUD (2016, background): “For instance, gravitationally unstable disk models often show clumps that have yet to collapse into stellar objects migrating inward (Vorobyov & Basu 2006, 2010).”
RESOLVING THE LUMINOSITY PROBLEM IN LOW-MASS STAR FORMATION (2011, methodology): “This is a natural consequence of the fact that these models feature average mass accretion rates that decrease with time (Vorobyov & Basu 2010; see Figure 2), thus the first 50% of the mass will accrete from the core faster than the second 50% of the mass.”
Dynamics of Protoplanetary Disks (2010, background): “Accretion in this regime is highly variable, due to a combination of the dominance of global modes (Forgan et al. 2010, Laughlin & Bodenheimer 1994), the effect of infall, and the formation and disruption of clumps (Boley et al. 2010, Vorobyov & Basu 2010).”
Formation of Supermassive Black Hole Seeds (2016, background): “In fact, 3D radiation hydrodynamical simulations by Hosokawa et al. (2015) show that clump migration leads to intermittent accretion (also see Vorobyov & Basu (2010) and (Vorobyov et al. 2013)) and disk fragmentation does not halt the formation of massive stars.”