A Numerical Study of Jets from Tilted BlackHole Accretion Disks

1
A Numerical Study of Jets from Tilted Black-Hole
Accretion Disks

• Chris Lindner
• PI P. Chris Fragile
• College of Charleston

2
Relativistic Jets

• High Speed
• High Energy
• Observable in X-Ray and sometimeseven visible
  and radio spectrums

Images courtesy of NASA and ATNF
NGC 4261 Radio and visible image
M87Hubble Space Telescope Visible
PKS 2356-61
Radio and visible image
3
The Source Black Hole Accretion Disks

• Often formed from binary star systems
• 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

4
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

Total intensity image at 4.85 GHz of SS433
Blundell, K. M. Bowler, M. G., 2004, ApJ, 616,
L159
5
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

6
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

7
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)

8
Untilted Disk Jets
Unbound Material
Magnetic Field Lines
9
15 Degree Tilt Jets
Unbound Material
Magnetic Field Lines
10
Future Work

• Further analysis of jet orientation and power
• Run simulations out further
• Compare power and orientation diagnostics
• Is jet orientation dependant on other parameters?
• Black Hole Spin
• Disk thickness
• Jet precession?

11
Untilted Disk Jets
Unbound Material
Magnetic Field Lines
12
15 Degree Tilt Jets
Unbound Material
Magnetic Field Lines
13
The Cubed Sphere
Six cubes are projected into segments of a sphere
Each block has its own coordinate system
14
Jet Orientation