Numerical simulation of astrophysical jets and accretion disks

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Numerical simulation of astrophysical jets and
accretion disks

• P. Rossi (INAF)
• G. Bodo (INAF)
• A. Ferrari (UniTO)
• S. Massaglia (UniTO)
• A. Mignone (INAF, UniTO)

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Physics of accretion-ejection flows
They are present in many astrophysical
environments Young Stellar Objects X-ray
binaries Active Galactic Nuclei ..
Numerical simulations of HD, MHD, relativistic
flows are essential for studying such problems

• Angular momentum transport in accretion disks
• Jet acceleration and collimation
• Emission from shocks in YSO jets
• Jet interaction with the ambient medium,
  deceleration
• of relativistic jets

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Accretion flows are ubiquitous in astrophysics
they occur around protostars, accreting compact
objects in binary systems, supermassive black
holes at the cores of galaxies. Accretion flows
are mainly in the form of accretion disk
AGN
YSO
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Collimated, supersonic outflows (jets) are
generated in many astrophysical environments
AGN
pulsars
YSO
X-ray transients
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Angular momentum transport in accretion disks

• If angular momentum is conserved matter just
  orbits the central object
• Accretion rate is determined by the outward
  transport of angular momentum

• Frictional or viscous transport too inefficient
  to explain observed luminosities
• Something many orders of magnitude more
  efficient is needed
• Shakura Sunyaev (1973) assumed transport was
  due to turbulence in the
• disc. Introduced ??parameter.
• Origin of turbulence magnetorotational
  instability (Balbus Hawley 1991)

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Questions ???
What is the value of ???
How ??depends on disk physical parameters ?
Numerical simulations of MRI
What are the effects of the numerics?
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Local versus global simulations
In a cartesian frame of reference corotating
with the disk
Advantages Higher resolution Longer time
integration
PLUTO code Plutocode.to.astro.it
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Despite big effort still many questions still
open?
Local simulations are meaningful only if they
capture correctly the dynamics of MRI driven
turbulence and the associated angular momentum
transport in the full disk
Global simulations with suitable resolution on
the limit of present possibilities
Are local simulations self-consistent? Solutions
are indeed local?
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Channel solution in correspondence of peaks
of Maxwell stresses
(Sano Inutsuka 2001)
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128x 512x 128
512x 512x 128
Still dependence on vertical box size? Reexamine
dependence on parameters
Introduce stratification
Global simulations
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Maximum
Minimum
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Fanaroff-Riley classification
Deceleration of relativistic jets

• FR I
• or jet dominated
• FR II
• or lobe dominated
• classical doubles

3C 449 VLA
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On parsec scale all jets are relativistic. In
FRI jet asymmetry decreases at larger scales
transition to subrelativistic regime
Faster spine Lower velocity layer Which
are the processes that lead to jet deceleration
? We investigate the effects of the
interaction between jet and ambient medium
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Numerical Approach
plutocode.to.astro.it
High resolution 20 pts on jet radius
Non uniform
grid Lower resolution 12 pts on jet radius
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JET INSTABILITY AND DECELERATION
Jet KH instabilities linear growth lKH increases
with MJ and g
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Grid size 1000x350x350 24 points on the jet radius
1) M3 h1000 G10 t760
2) M30 h10 G10 t265
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1)
2)
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Doppler boosting
Jet velocity structure
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Conclusions
The fundamental parameter is the density
ratio The final velocity structure presents a
relativistic core subrelativistic layer well
distinct Agreement with radio observations
But. Our layer is too slow we will explore in
more details the parameter space and we will
introduce the magnetic field, that at the moment
is missing .