1 07/10/2010 - Séminaire du LUTh - Jérôme Guilet Asymmetric explosions of Core collapse...
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Transcript of 1 07/10/2010 - Séminaire du LUTh - Jérôme Guilet Asymmetric explosions of Core collapse...
107/10/2010 - Séminaire du LUTh - Jérôme Guilet
Asymmetric explosions of
Core collapse supernovae
Jérôme Guilet
En collaboration avec Thierry Foglizzo, Sébastien Fromang & Jun’ichi Sato
207/10/2010 - Séminaire du LUTh - Jérôme Guilet
Outline
Introduction: Asymmetry in Core Collapse supernovae
The Standing Accretion Shock Instability The linear growth mechanism
The saturation of SASI
Effect of a magnetic field SASI in a magnetized flow
Dynamics of an Alfvén surface
Conclusions and perspectives
307/10/2010 - Séminaire du LUTh - Jérôme Guilet
Supernova : death of a star
•Extremely powerful/bright explosion
•SN Ia : thermonuclear explosion
(not discussed here)
•SN II : Collapse of the core of a massive star
=> formation of a neutron star
•Electromagnetic waves detected days after the explosion : the central engine is difficult to detect
•Gravitational waves and neutrinos would give a view of the instant of explosion
407/10/2010 - Séminaire du LUTh - Jérôme Guilet
Polarization Pulsar kicks
Indications of explosion asymmetry
Pulsars have high peculiar velocities : ~ 400 km.s-1, up to >1000 km.s-1
probably originated fromasymmetries in supernovaexplosion
guitar nebula
507/10/2010 - Séminaire du LUTh - Jérôme Guilet
From core collapse to the stalled shock
Stalled shock
How to revive the shock and obtain an explosion ?
massive star
collapse of the iron core
607/10/2010 - Séminaire du LUTh - Jérôme Guilet
heating
cooling
From the stalled shock to an explosion ???
•Classical delayed neutrino-driven mechanism :
•Many physical ingredients :– Nuclear physics– Neutrino transport– General relativity– Multi-Dimensional hydrodynamics– Magnetic field
-->Extremely challenging numerical task !
•No explosion in the most sophisticated 1D simulations... (Liebendorfer et al 2001)
Asymmetries are essential for the explosion mechanism !!
Neutrino heating below the shock
drives the explosion
Protoneutron
star
neutrinosphere(r~30-80km)
shock(r~200km) gain radius
collapsing core
707/10/2010 - Séminaire du LUTh - Jérôme Guilet
Breaking the spherical symmetry
•Due to neutrino heating below the shock•small angular scale : l ~ 4-5
•Induces shock oscillations•large angular scale : l ~ 1-2
Neutrino driven convection Standing Accretion Shock Instability (SASI) Blondin et al 2003
induces a global asymmetry !
Foglizzo et al 2006 Foglizzo et al 2006
807/10/2010 - Séminaire du LUTh - Jérôme Guilet
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Neutrino driven explosion Acoustic explosion
- SASI and convection help neutrino heating by increasing the dwell time in the gain region
A marginal explosion in 2D ? (Marek & Janka 2009)
Robust explosion in 3D ?? (Nordhaus et al. 2010)
Marek & Janka 2009 Burrows et al. 2006
- SASI induces g-mode oscillations of the neutron star
- Acoustic power revives the shock
907/10/2010 - Séminaire du LUTh - Jérôme Guilet
Important consequences of SASI
•Global asymmetry of the explosion :
– polarization observation
– profile of oxygen line
•Could explain neutron star kicks up to 1000 km/s (Scheck et al 2006, Wongwathanarat et al 2010)
•Affect the neutron star spin (Blondin & Mezzacappa 2007)
•Gravitational waves emission (e.g. Kotake et al 2009, Marek et al 2009)
Wongwathanarat et al 2010
Blondin & Mezzacappa 2007
1007/10/2010 - Séminaire du LUTh - Jérôme Guilet
Outline
Introduction: Asymmetry in Core Collapse supernovae
The Standing Accretion Shock Instability The linear growth mechanism
The saturation of SASI
Effect of a magnetic field SASI in a magnetized flow
Dynamics of an Alfvén surface
Conclusions and perspectives
1107/10/2010 - Séminaire du LUTh - Jérôme Guilet
Methods
•Perturbative analysis :– stationary flow
=>simplifying assumptions– add small perturbations– compute eigenmodes
• growth rates• frequencies• eigenfunctions: spatial distribution
•Numerical simulations :– No need for a stationnary flow– Can describe the non linear dynamics
growth rate
shock position
Foglizzo et al 2007
1207/10/2010 - Séminaire du LUTh - Jérôme Guilet
Two competing mechanisms
Purely acoustic mechanismAdvective-acoustic cycle
neutronstar
shock
entropy-vorticity wave
neutronstar
shock
acoustic wave acoustic wave
Foglizzo et al 2007 Blondin & Mezzacappa 2006
Advective-acoustic cycle favored by a WKB analysis
BUT : valid for high frequency modes only...
1307/10/2010 - Séminaire du LUTh - Jérôme Guilet
SASI mode frequencies
•Fundamental frequency (most unstable mode) is consistent with both mechanisms
(Foglizzo et al 2007, Scheck et al 2008)
•Higher harmonics inconsistent with the purely acoustic mechanism (Guilet & Foglizzo in prep)
frequencyrsh = 2.5rPNS
Advective-acoustic cycle wins !
1407/10/2010 - Séminaire du LUTh - Jérôme Guilet
Outline
Introduction: Asymmetry in Core Collapse supernovae
The Standing Accretion Shock Instability The linear growth mechanism
The saturation of SASI
Effect of a magnetic field SASI in a magnetized flow
Dynamics of an Alfvén surface
Conclusions and perspectives
1507/10/2010 - Séminaire du LUTh - Jérôme Guilet
Saturation by parasitic instabilities
advective-acoustic cycle
=> Saturation
entropy-vorticity wave
1607/10/2010 - Séminaire du LUTh - Jérôme Guilet
The parasitic instabilities
Entropy wave :
Rayleigh-Taylor instability
Vorticity wave :
Kelvin-Helmholtz instability
Stabilizing effects for the parasites :• Stratification (Stationary entropy caused by neutrino cooling) :
Efficient near the neutron star• Advection : efficient just below the shock
1707/10/2010 - Séminaire du LUTh - Jérôme Guilet
QuickTime™ et undécompresseur
sont requis pour visionner cette image.
QuickTime™ et undécompresseur
sont requis pour visionner cette image.
small amplitude entropy wave large amplitude entropy wave
potential step decelerating the flow
1807/10/2010 - Séminaire du LUTh - Jérôme Guilet
Efficiency of the acoustic feedback
Kelvin-Helmholtz(entropy-vorticity wave)
Rayleigh-Taylor(entropy wave)
1907/10/2010 - Séminaire du LUTh - Jérôme Guilet
Dissociation energy increases & neutrino cooling decreases
Fernandez &Thompson 2009
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Scheck et al 2008
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
2007/10/2010 - Séminaire du LUTh - Jérôme Guilet
Estimate of the saturation amplitude
•Criterion :
•Result : Rayleigh-Taylor is responsible for the saturation
Stratification advectionSASI growth rate
This saturation mechanism seems to work well !
Guilet et al 2010
2107/10/2010 - Séminaire du LUTh - Jérôme Guilet
Outline
Introduction: Asymmetry in Core Collapse supernovae
The Standing Accretion Shock Instability The linear growth mechanism
The saturation of SASI
Effect of a magnetic field SASI in a magnetized flow
Dynamics of an Alfvén surface
Conclusions and perspectives
2207/10/2010 - Séminaire du LUTh - Jérôme Guilet
QuickTime™ et undécompresseur TIFF (LZW)
sont requis pour visionner cette image.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Neutrino driven explosion Magnetic explosion
- no magnetic field
- Magnetic field amplification: B ~1015 G
- Obtains for VERY rapid rotation
Marek & Janka 2009
Burrows et al. 2007
Moderate field effect ?
2307/10/2010 - Séminaire du LUTh - Jérôme Guilet
Outline
Introduction: Asymmetry in Core Collapse supernovae
The Standing Accretion Shock Instability The linear growth mechanism
The saturation of SASI
Effect of a magnetic field SASI in a magnetized flow
Dynamics of an Alfvén surface
Conclusions and perspectives
2407/10/2010 - Séminaire du LUTh - Jérôme Guilet
A toy model for SASI in a magnetized flow
neutronstar
shock
or
B
planar adiabatic toy model(Foglizzo 2009)
x
z v
« neutron star »
shock
deceleration byan external potential
Advective-acoustic cycle with a magnetic field : vorticity can propagate through Alfvén and slow waves !
decelerated flow
supersonic flow
neutrino cooling
2507/10/2010 - Séminaire du LUTh - Jérôme Guilet
Interference between vorticity cycles
Propagation of the vorticity
different cycles are out of phase
Entropy
Vorticity : Alfvén and slow waves
Wave - Wave +
choc
~vA~Bgrowth rate
magnetic field strength
The advective-acoustic cycle separates in up to 5 cycles !
Guilet & Foglizzo 2010
2607/10/2010 - Séminaire du LUTh - Jérôme Guilet
Coupling efficiency
-Vertical B : No effect
-Horizontal B : - Strong amplification of the
vorticity cycles when field lines are bent (k // B)
- Increase of the growth rate
- Significant effect if vA~v
magnetic field strength
growth rate
coupling efficiency
Conclusion : Ambiguous result...
2707/10/2010 - Séminaire du LUTh - Jérôme Guilet
Outline
Introduction: Asymmetry in Core Collapse supernovae
The Standing Accretion Shock Instability The linear growth mechanism
The saturation of SASI
Effect of a magnetic field SASI in a magnetized flow
Dynamics of an Alfvén surface
Conclusions and perspectives
2807/10/2010 - Séminaire du LUTh - Jérôme Guilet
Alfvén surface simulations
•The alfvén surface is defined by : v = vA
Alfvén speed : vA2 = B2/(
•An Alfvén wave propagates against the flow at the speed : v-vA
•Accumulation of Alfvén waves at the Alfvén surface !
•We performed 1D simulations with the code RAMSES
2907/10/2010 - Séminaire du LUTh - Jérôme Guilet
Alfvén wave amplification and pressure feedback
•The Alfvén wave amplifies while its wavelength decreases (Williams 1975) :
•When the wavelength is as small as the dissipative scale, the Alfvén wave is dissipated
•Creation of a pressure feedback that increases the upstream pressure
z
deceleration
Alfvén surface
3007/10/2010 - Séminaire du LUTh - Jérôme Guilet
Analytical estimate versus simulations
Small amplitude Alfvén wave Non linear saturation
frequency
incident amplitude
(Guilet et al submitted to ApJ)
3107/10/2010 - Séminaire du LUTh - Jérôme Guilet
How does this affect core collapse ?
•Fast enough amplification if the Alfvén surface is above the proto-neutron star surface
•Magnetic field required :
•SASI creates Alfvén waves with an amplitude :
•Amplitude of the pressure feedback (from the analytic estimate) :
Pressure increase pushes the shock :
-> might help the explosion
-> change the geometry
Important effect !!!
3207/10/2010 - Séminaire du LUTh - Jérôme Guilet
Outline
Introduction: Asymmetry in Core Collapse supernovae
The Standing Accretion Shock Instability The linear growth mechanism
The saturation of SASI
Effect of a magnetic field SASI in a magnetized flow
Dynamics of an Alfvén surface
Conclusions and perspectives
3307/10/2010 - Séminaire du LUTh - Jérôme Guilet
Conclusions
•Multidimensional dynamics is important in core collapse supernovae
•SASI can be attributed to the advective-acoustic cycle
•The saturation of SASI can be explained by the appearance of parasitic instabilities (Rayleigh-Taylor instability)
•The magnetic field could have an important effect when vA ~ v, even if the magnetic pressure is negligible
– SASI could be either stabilized or amplified
– Alfvén wave amplification at the Alfvén surface creates an important pressure feedback
3407/10/2010 - Séminaire du LUTh - Jérôme Guilet
Perspectives
•Dependence of the SASI amplitude on the physical ingredients ?
– Heating, cooling by neutrinos– Equation of state– Rotation...
•Analytical estimate of consequences of SASI :– amplitude of the kick, – spin of the NS, – gravitational wave signal...
•Effect of a more realistic magnetic field geometry ?
•Multidimensional dynamics at the Alfvén surface ? Effect of the turbulence of the flow ?
Merci de votre attention!
Dipolar magnetic field
3507/10/2010 - Séminaire du LUTh - Jérôme Guilet
Frequencies and associated timescales
•Fundamental mode (most unstable)
– advective-acoustic time
– azimuthal acoustic time
•Higher harmonics :
-> radial propagation time...
Acoustic modes of a box
Lz
Lx
Analogy
Lr=rsh-r*
Lx=r
frequency
3607/10/2010 - Séminaire du LUTh - Jérôme Guilet
Radial time in a simplified model of SASI
acoustic
advective-acoustic
timescale
Extracted from SASI eigenspectrum :
shock position