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Simulations of Jets from Black-Hole Accretion Disks Chris Lindner UT Austin PI: P. Chris Fragile College of Charleston Collaborators: Peter Anninos, Jay.

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Presentation on theme: "Simulations of Jets from Black-Hole Accretion Disks Chris Lindner UT Austin PI: P. Chris Fragile College of Charleston Collaborators: Peter Anninos, Jay."— Presentation transcript:

1 Simulations of Jets from Black-Hole Accretion Disks Chris Lindner UT Austin PI: P. Chris Fragile College of Charleston Collaborators: Peter Anninos, Jay Salmonson

2 Relativistic Jets Images courtesy of NASA and ATNF High Speed High Energy Observable in X-Ray and sometimes even visible and radio spectrums M87 Hubble Space Telescope Visible NGC 4261 Radio and visible image PKS Radio and visible image

3 Relativistic Jets Minkowskis Object Radio emissions overlaid in red Jet from an AGN Crab Nebula Jet from a Neutron Star Active Galaxy Centaurus A

4 Simulating Tilted Black Hole Accretion disks End of a stars life Gravity bends light around it It bends to the point where no light can escape! Can be found at the center of almost every galaxy

5 Simulating Tilted Black Hole Accretion disks We cant see black holes… …but we can study how their gravity affects the objects around them

6 Black Hole Accretion Disk Systems X-ray binary star systems and galaxy nuclei Black hole accretes matter from donor star Disk of plasma forms around black hole Angular momentum is exchanged through Magnetic fields Magnetically dominated flux points away from black holes poles, forming jets

7 What is a jet? Poynting Flux Jet – EM jet described by Blandford-Znajek Mechanism located in evacuated funnel Funnel Wall jet – gas-pressure launched material jet surrounding the poyting flux region Total Pressure (gas plus magnetic) Hawley & Krolik, 2006

8 Magnetic fields are enhanced via angular momentum transport Leads to a strong polar magnetic field The Magneto Rotational Instability and Blandford-Znajek Mechanism Blandford and Znajek 1977 Positron-electron pair creation could create spark gaps in B fields, and acceleration of these charges could lead to observed emissions

9 Jets: What we dont know What powers the jets? What sets Jet orientation? Not all jets are perfectly linear Some form corkscrew patterns, indicating jet precession Binary systems have been observed where jet orientations dont match the angular momentum of the accreting object How is the black hole oriented? Currently, this cannot be determined by observation alone Blundell, K. M. & Bowler, M. G., 2004, ApJ, 616, L159 Total intensity image at 4.85 GHz of SS433

10 Why do Computational Astrophysics? Tests the extremes of space that cannot be experimentally recreated Many vital parameters cannot be observed Many problems have no exploitable symmetry

11 Finite Volume Simulations Divide the computational area into zones Each zone contains essential data about the material contained inside The simulation is evolved in time through a series of time steps As the simulation progresses, cells communicate with each other – calculate

12 GRMHD Equations in Cosmos++ Extended Artificial Viscosity (eAV) mass conservation momentum conservation induction divergence cleanser

13 Highlights of Cosmos++ Developers: P. Anninos, P. C. Fragile, J. Salmonson, & S. Murray – Anninos & Fragile (2003) ApJS, 144, 243 – Anninos, Fragile, & Murray (2003) ApJS, 147, 177 – Anninos, Fragile & Salmonson (2005) ApJ, 635, 723 Multi-dimensional Arbitrary-Lagrange-Eulerian (ALE) fluid dynamics code – 1, 2, or 3D unstructured mesh Local Adaptive Mesh Refinement (Khokhlov 1998)

14 Highlights of Cosmos++ Multi-physics code for Astrophysics/Cosmology – Newtonian & GR MHD – Arbitrary spacetime curvature (K. Camarda -> Evolving GRMHD) – Relativistic scalar fields – Radiation transport (Flux-limited diffusion -> Monte Carlo) – Equilibrium & Non-Equilibrium Chemistry (30+ reactions) – Radiative Cooling – Newtonian external & Self-gravity Developed for large parallel computation – LLNL Thunder, NCSA Teragrid, NASA Columbia, JPL Cosmos, BSC MareNostrum, UT Lonestar, UT Ranger

15 Relativistic Jets in Simulation Angular momentum supported torus surrounding a rotating black hole Weak seed dipole magnetic field (poloidal) Low density background Minor initial fluctuations to foster instabilities Mass disk << Mass BH Simulated for low number of orbital periods

16 Relativistic Jets in Simulation McKinney 2005 Log Density (~10 orders of magnitude between dark red and blue) Magnetic Field Geometry

17 Simulating Tilted Black Hole Accretion disks Black holes spin Accretion Disks Spin Do they have to spin together? Could this explain jet precession?

18 What determines jet orientation in accretion disk systems? We can answer this question by simulating systems where the angular momentum of the disk is not aligned with the angular momentum of The black hole Tilted accretion disks (Fragile, Mathews, & Wilson, 2001, Astrophys. J., 553, 955) Can arise from asymmetric binary systems Breaks the main degeneracy in the problem

19 Initial tilted-disk simulations [Show Movies]

20 Initial tilted-disk simulations Standing shock along line of nodes creates accretion streams Increase in accretion rate Observable precession No Bardeen-Petterson effect observed No Jets!!! Interesting physics.. but

21 Spherical-Polar Grid Most commonly used type of grid for accretion disk simulations –good angular momentum conservation –easy to accommodate event horizon Not very good for simulating jets in 3D –zones get very small along pole forcing a very small integration timestep –pole is a coordinate singularity creates problems, particularly for transport of fluid across the pole

22 Cubed-Sphere Grid Common in atmospheric codes Not seen as often in astrophysics Adequate for simulating disks –good angular momentum conservation –easily accommodates event horizon Advantages for simulating jets –nearly uniform zone sizing over entire grid –no coordinate singularities (except origin)

23 The Cubed Sphere Each block has its own coordinate system Six cubes are projected into segments of a sphere

24 Untilted Disk Jets Magnetic Field Lines Unbound Material

25 Untilted Disk Jets Scaled as 6 x (Mjet/Mtorus) MassFluxRMax = Blue UnboundMassFlux = Black DeVilliers, Hawley & Krolik 2004 (x10^6 – 6x10^6)

26 Possible Issues Unphysical or physical numerical reconnection Mass loading Lack of angular momentum conservation in funnel region … or maybe previous simulations are too symmetric?

27 Conclusions Two types of jets: Poynting flux and matter (funnel wall) Jets do form in MHD simulations – Do not require initial large-scale magnetic fields Further study is needed in the area of jet orientation and eliminating symmetries (and were working on it!)

28

29 Late time evolution of Gamma Ray Bursts Light curve decays rapidly in Gamma ray burst Is it a product of Central engine activity? Is there enough material to feed a jet?

30 Relativistic Jets in Simulation Beckwith, Hawley, and Krolik 2008Hawley, and Krolik 2005 Plasma β Magnetosonic Mach Number

31 Hawley & Krolik 2005 Untilted Disk Jets

32 Magnetosonic Mach Number Late Time Hawley & Krolik 2005


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