The effect of partial ionisation in star formation James Wurster - - PowerPoint PPT Presentation
The effect of partial ionisation in star formation James Wurster with Matthew Bate & Daniel Price 1 st Phantom Users Workshop Monash University, 23 February 2018 Non-ideal magnetohydrodynamics Ambipolar Diffusion (dissipative) Hall
with Matthew Bate & Daniel Price 1st Phantom Users Workshop Monash University, 23 February 2018
Adapted from Wardle (2007)
Ambipolar Diffusion (dissipative) Hall Effect (non-dissipative) Ohmic Resistivity (dissipative)
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Image credit: Tsukamoto et al (2017); see also: Braiding & Wardle (2012a,b)
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ØInitial conditions: Ø1 Msun of gas ØUniform density ØStrong magnetic fields (µ0 = 5) ØΩ.B < 0 (primary suite) ØΩ.B > 0 (secondary suite) ØProcesses included: ØNon-ideal MHD ØOhmic resistivity ØHall Effect ØAmbipolar diffusion
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Wurster, Bate & Price (2018b)
iMHD ρmax=10-15g cm-3 ζ12 ζ13 ζ14 ζ15 ζ16 ζ17 ζ18 ζ19 ζ20 ζ22 ζ23 ζ24 ζ25 ζ30
log density [g/cm3] 500 AU HD ρmax=10-13g cm-3
log density [g/cm3] 150 AU ρmax=10-12g cm-3
log density [g/cm3] 30 AU
Ø Images are log(density). Ø Rows are ρ = 10-15 g cm-3, ρ = 10-13 g cm-3, ρ = 10-12 g cm-3 𝜂 = 10-17 s-1 Ideal MHD Hydrodynamic 𝜂 = 10-18 s-1 𝜂 = 10-16 s-1
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Wurster, Bate & Price (2018b)
iMHD ρmax=10-15g cm-3 ζ12 ζ13 ζ14 ζ15 ζ16 ζ17 ζ18 ζ19 ζ20 ζ22 ζ23 ζ24 ζ25 ζ30
log density [g/cm3] 500 AU HD ρmax=10-13g cm-3
log density [g/cm3] 150 AU ρmax=10-12g cm-3
log density [g/cm3] 30 AU
Ø Images are log(density). Ø Rows are ρ = 10-15 g cm-3, ρ = 10-13 g cm-3, ρ = 10-12 g cm-3 𝜂 = 10-17 s-1 Ideal MHD Hydrodynamic 𝜂 = 10-18 s-1 𝜂 = 10-16 s-1
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Wurster, Bate & Price (2018b)
ρmax ideal MHD =10-12g cm-3 ζcr=10-13s-1 ζcr=10-14s-1 ζcr=10-15s-1 ζcr=10-16s-1 ζcr=10-17s-1 ζcr=10-18s-1
log density [g/cm3] Hydro
log |B|
vr [km/s]
50 vy [km/s]
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Wurster, Bate & Price (2018b)
ρmax=10-12g cm-3
log |B| 30 AU ρmax=10-12g cm-3 iMHD ζ12 ζ13 ζ14 ζ15 ζ16 ζ17 ζ18 ζ19 ζ20 ζ22 ζ23 ζ24
log density [g/cm3] 30 AU Hydro ρmax=10-12g cm-3
vr [km/s] 30 AU ρmax=10-12g cm-3
50 vy [km/s] 30 AU
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Wurster, Bate & Price (2018b)
100 101 102 103 104 105 106 107 10-17 10-16 10-15 10-14 10-13 10-12 10-11 cpu time [h] ρmax [g cm-3] iMHD HD ζ10 ζ16 ζ17 ζ18 ζ19 ζ20 ζ22 ζ23 ζ24 ζ25 ζ30
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Video available at https://www.youtube.com/watch?v=CgErHuWdcPw&t=3s
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Wurster, Bate & Price (2018a)
10-16 10-12 10-8 10-4 100 ni/(ni+nn) ρmax=10-10g cm-3 ζ12 ζ14 ζ15 ζ16 10-16 10-12 10-8 10-4 100 ni/(ni+nn) ρmax=10-7g cm-3 10-16 10-12 10-8 10-4 100 ni/(ni+nn) ρmax=10-4g cm-3; dtsc=0 10-16 10-12 10-8 10-4 100 10-4 10-3 10-2 10-1 100 101 102 ni/(ni+nn) r [au] dtsc=0.5yr 10-14 10-12 10-10 10-8 10-6 10-4 10-2 100 24400 24600 24800 25000 25200 ρmax[g cm-3] Time [yr] iMHD ζ12 ζ14 ζ15 ζ16 HD
10 ζ ζ ζ ζ 10-4 10-2 100 102 104 106 10-18 10-16 10-14 10-12 10-10 10-8 10-6 10-4 10-2 100 Bmax [G] ρmax [g cm-3]
ζ ρ ζ ζ z [AU] x [AU]
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50
2 log |B| [G] ζcr=10-16s-1 z [AU] x [AU]
50
50
2 vy[km/s] z [AU]
50 ζcr=10-12s-1 ρmax=10-7g cm-3 ζ ζ ζ z [AU]
50 50
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z [AU]
50 ζcr=10-12s-1 ρmax=10-7g cm-3 ζ ζ ζ
Wurster, Bate & Price (2018a)
ζ ρ ζ ζ z [AU] x [AU]
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50
2 vr [km/s] ζcr=10-16s-1
12 12 28 au ζcr=10-12s-1 dtsc=0.5yr
5 10 vr[km/s] 7 au
5 vφ [km/s]
Wurster, Bate & Price (2018a)
28 au ζcr=10-16s-1 dtsc=17yr
5 vr[km/s] 7 au
5 vφ [km/s]
z [AU]
1 ζcr=10-12s-1 dtsc=0.5yr ζ ζ ζ ζ ζ ζ z [AU] x [AU]
1
1
2 log |B|[G] ζcr=10-16s-1
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Wurster, Bate & Price (2018a)
ØModelled the collapse of a molecular cloud core through the first core to stellar densities; included Ohmic resistivity, ambipolar diffusion, the Hall effect ØThe coefficient of the Hall effect is similar to the ambipolar diffusion in the medium surrounding the core ØHigh cosmic ray ionisation rates can reproduce ideal MHD collapses ØLow cosmic ray ionisation rates can approximate hydrodynamicals collapses, but cannot reproduce them ØDecreasing the cosmic ionisation rate increases the lifetime of the first hydrostatic core ØThe first and second hydrostatic cores become thermally ionised, but the accreting material is still only ionised by cosmic rays ØThe second core outflow is suppressed at low cosmic ray ionisation rates
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j.wurster@exeter.ac.uk http://www.astro.ex.ac.uk/people/wurster/