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Abstract In certain scenarios, the accreted angular momentum of plasma onto a black hole could be low; however, how the accretion dynamics depend on the angular momentum content of the plasma is still not fully understood. We present three-dimensional, general relativistic magnetohydrodynamic simulations of low angular momentum accretion flows around rapidly spinning black holes (with spina = +0.9). The initial condition is a Fishbone–Moncrief (FM) torus threaded by a large amount of poloidal magnetic flux, where the angular velocity is a fractionfof the standard value. Forf= 0, the accretion flow becomes magnetically arrested and launches relativistic jets but only for a very short duration. After that, free-falling plasma breaks through the magnetic barrier, loading the jet with mass and destroying the jet–disk structure. Meanwhile, magnetic flux is lost via giant, asymmetrical magnetic bubbles that float away from the black hole. The accretion then exits the magnetically arrested state. Forf= 0.1, the dimensionless magnetic flux threading the black hole oscillates quasiperiodically. The jet–disk structure shows concurrent revival and destruction while the gas outflow efficiency at the event horizon changes accordingly. Forf≥ 0.3, we find that the dynamical behavior of the system starts to approach that of a standard accreting FM torus. Our results thus suggest that the accreted angular momentum is an important parameter that governs the maintenance of a magnetically arrested flow and launching of relativistic jets around black holes.
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Young Stellar Object Jets Magnetocentrifugally Driven by Reconnecting Atmospheric Avalanche Accretion Streams above Inner Circumstellar Disks
Abstract Fast, collimated jets are ubiquitous features of young stellar objects. They are generally thought to be powered by disk accretion, but the details are debated. Through 2D (axisymmetric) MHD simulations, we find that a fast (>100 km s−1) collimated bipolar jet is continuously driven along the north and south poles of a circumstellar disk that is initially magnetized by a large-scale open poloidal field and contains a thermally ionized inner magnetically active zone surrounded by a dead zone. The fast jet is primarily driven magnetocentrifugally by the release of the gravitational binding energy of the so-called “avalanche accretion streams” near the boundary of an evacuated poloidal field dominated polar region and a thick disk atmosphere raised by a toroidal magnetic field. Specifically, the fast outflow is driven along the upper (open) branch of the highly pinched poloidal field lines threading the (strongly magnetically braked) accretion streams, where the density is relatively low so that the lightly loaded material can be accelerated magnetocentrifugally along the open field line to a high speed. The highly pinched poloidal magnetic fields threading the avalanche accretion streams tend to reconnect, enabling mass to accrete to the center without dragging along the poloidal magnetic flux with it. The reconnection provides a potential heating source for producing chondrules and calcium- and aluminum-rich inclusions.
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- Award ID(s):
- 2307199
- PAR ID:
- 10562165
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 978
- Issue:
- 1
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 84
- Size(s):
- Article No. 84
- Sponsoring Org:
- National Science Foundation
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