Seminars & Lectures
| * TITLE | Mechanism that removes accretion disk angular momentum while driving associated bi-directional astrophysical jets | ||||||
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| * DATE / TIME | 2016-07-06, 4 PM | ||||||
| * PLACE | Hogil Kim Memorial Hall Classroom 307 | ||||||
| * ABSTRACT | |||||||
| I propose a mechanism [1] that simultaneously drives astrophysical jets and removes angular momentum from an accretion disk. The mechanism depends on (i) the very great difference in ionization between the weakly ionized accretion disk and the highly ionized exterior region and (ii) the complete circuit of poloidal electric current. In the highly ionized exterior region collisionless Hamiltonian mechanics and axisymmetry constrain charged particles to move on nested poloidal flux surfaces whereas in the weakly ionized accretion disk particle motion is very different. The weak ionization in the disk means that ions in the disk collide very frequently with neutrals so any momentum a disk ion gains electromagnetically is immediately shared with nearby neutrals. A fluid element consisting of ions and neutrals thus behaves as if it has the charge of the ions and the mass of the neutrals. This fluid element consequently behaves dynamically like a collisionless meta-particle having charge to mass ratio reduced from than that of an ion by the nominal accretion disk 10^-15 – 10^-8 fractional ionization. This means that the meta-particle cyclotron frequency can be of the order of the Kepler angular frequency in which case meta-particles with a critical charge to mass ratio have zero canonical angular momentum. Hamiltonian dynamics shows that meta-particles with zero canonical angular momentum experience no centrifugal force and spiral inward towards the central body [2]. Because the metaparticles are positively charged, the accumulation of inward spiraling meta-particles near the central body produces radially and axially outward electric fields. The axial outward electric field drives an out-of-plane poloidal electric current along arched poloidal flux surfaces in the collisionless region external to the disk. This out-of-plane poloidal current and its associated toroidal magnetic field produce forces that drive bidirectional astrophysical jets flowing normal to and away from the disk [3,4]. The poloidal electric current circuit is completed in the disk by a radially inward current that removes angular momentum from the accreting mass in the disk via a $-r J_r B_z$ counter-torque. The complete poloidal electric circuit removes disk angular momentum and transports it electrically to infinity in the disk plane in a manner analogous to how wires connecting an electric generator to a distant electric motor transport angular momentum from the generator to the motor. The disk region is an electric power source (E⋅J<0) while the jet region is an electric power sink (E⋅J>0). [1] P. M. Bellan, Monthly Notices Royal Astron. Soc., in press [2] P. M. Bellan, Physics of Plasmas 14, 122901 (2007). [3] D. Kumar and P. M. Bellan, Physical Review Letters 103, 105003 (2009) [4] X. Zhai, H. Li, P. M. Bellan, and S. Li, ApJ 791, 40 (2014). -Supported by USDOE and NSF. |
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| * ABSTRACT FILE | 2016-Bellan-Integreated-jet-disk-model-Korea-visit.docx | ||||||
