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Magnetohydronamic Production of Relativistic Jets Nick Cowan UW Astronomy December 2004 QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture.

Magnetohydronamic Production of Relativistic Jets Nick Cowan UW Astronomy December 2004

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Magnetohydronamic Production of Relativistic Jets

Nick Cowan

UW Astronomy

December 2004

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Do these things really exist?

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M87 in the Radio

Guilty by Association

• Radio Galaxies and Quasars

• Microquasars• Supernovae• Gamma-ray bursts• T Tauri stars

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Good ol’ Crab

Synchrotron Radiation

• High brightness temperature

• Characteristic spectrum

• Highly polarized• Rapid variability (ns)

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Shocks

• Relativistic usually means supersonic

• The “hot spots” in many radio sources

• Nature’s own particle accelerator

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Superluminous Motion(How it looks)

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Superluminous Motion (How it works)

5 ly

3 ly

4 ly

V = 5/6 c

A

B

Light from A arrives here 2 yrs before light from B

Doppler Boosting & Focusing

D = sqrt(1 - 2) (1 - cos)

• Jet is D2 times brighter due to smaller solid angle

• Jet is D times brighter due to higher frequency of emission

Modelling MHD Jets: Some simplifying assumptions

Plasma behaves like a fluidPlasma is a perfect conductorFrozen-in field linesMagnetic pressureMagnetic tension

Limiting Cases

v2 < B2/8Plasma is flung out centrifugally along field lines

v2 > B2/8Field is bent back by rotating plasma

Characteristic Time Scales

d = R/cms

esc = (R3/2GM)1/2

d < esc Quasi-static outflow

d > esc Explosion or collapse

Recipe for a jet

Gravitating body+ Source of material+ Poloidal B-field+ Differential rotation Torsional Alfven

Wave Train (TAWT)

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Thick disks make powerful jets

• Jet is powered by the poloidal B-field

• Strength of poloidal field is proportional to (H/R)2

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R

H

Frame Drag

• Kerr black holes have angular momentum

• The space time near such a black hole is also rotating differentially

• This leads to more powerful jets

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Bringing it all together

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Power Jet

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Penis

References

• “Magnetohydrodynamic Production of Relativistic Jets” Meier, Koide, Uchida (2001)

• “Sources of Relativistic Jets in the Galaxy” Mirabel, Rodriguez (1999)

• “Hydromagnetic flows from accretion discs and the production of radio jets” Blandford, Payne (1982)