The Status of Core-Collapse
Supernova Explosion Modelling

Bernhard Müller
F. Hanke, L. Hüdepohl, J. v. Groote, H.-Th. Janka, A. Marek, T. Melson
Max-Planck-Institut für Astrophysik, Garching
I. Tamborra (U Amsterdam), G. Raffelt (MPI for Physics)

Major Questions inSupernova Theory●●

How does the “engine” work? Is
the -driven mechanism viable
or do we need something else?

What can we observe?
●Neutrinos – from bounce tocooling●Gravitational waves (?)●

Nucleosynthesis yields●Ejecta morphology, pulsar
kicks, light curves...

The Thorny Path towards Explosion
ModelsComputationalChallenges●Multi-dimensionality of the flow

●Multi-scale problem

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Transition between the diffusion &free streaming regimes of theneutrinos → kinetic theory required→ 6D problem
Nuclear & particle physics input
partly undeterminedseveral 100 km

Strong gravitational fields(GM/rc2≈0.1...0.2) & high velocities→ relativistic effects important
Combine all this in a first-principle
approach!
The most ambitious 3D models
currently take ~5000 core years

not to scale~108km

Why SN explosions have proved
difficult to obtain (in simulations...)
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Delicate sensitivity of heating/cooling to neutrino interaction rates:
tadv/theat~(LE2)5/3 → importance of accurate transport
General relativity only recently included in multi-dimensionaltransport simulations (Müller et al. 2010; first attempts in 3D: Kuroda
et al. 2012, Ott et al. 2013)
Long simulations (~1s) and 3D models not feasible until recently
Too few models: impact of progenitor variations (in the innermost<2M8) has long remained unexploredMore successful results recently reported (results & methods cannot
all be evaluated here):●MPA group: Marek & Janka (2009), Müller et al. (2012, 2013), Janka et al.
(2012)●Suwa et al. (2010, 2012), Takiwaki et al. (2012), Kuroda (2012)●

OakRidge group: Bruenn et al. (2009), Bruenn et al. (2012).

A Panoramic View of Multi-Group Neutrino
Hydrodynamics Simulations (MPA Group)

8.8 O-Ne-Mg core progenitor

9.6 M8, Z=0

8.1 M8, Z=10-4Z8

oscillatory“sloshing”

shock

11.2 M8
Janka et al. (2012)

15 M8
Evolution of the entropy along the polar axis
(show shock evolution, shell interfaces & neutrino-heated matter)

27 M8

A Panoramic View of Multi-Group Neutrino
Hydrodynamics Simulations (MPA Group)

8.8 O-Ne-Mg core progenitor

9.6 M8, Z=0

8.1 M8, Z=10-4Z8

oscillatory“sloshing”

shock

11.2 M8
Janka et al. (2012)

15 M8
Evolution of the entropy along the polar axis
(show shock evolution, shell interfaces & neutrino-heated matter)

27 M8

A Panoramic View of Multi-Group Neutrino
Hydrodynamics Simulations (MPA Group)

8.8 O-Ne-Mg core progenitor

9.6 M8, Z=0

8.1 M8, Z=10-4Z8

oscillatory“sloshing”

shock

11.2 M8
Janka et al. (2012)

15 M8
Evolution of the entropy along the polar axis
(show shock evolution, shell interfaces & neutrino-heated matter)

27 M8

A Large Variety of Ways Towards the Explosion
11.2 M8

8.8 O-Ne-Mg core progenitor

Supernovae with O-Ne-Mg
cores:●Robust explosions
obtained by 3 groups(MPA, Arizona, Basel)●Clue: Tenuous envelope
around iron core

New Class of Fast-Exploding Low-MassProgenitors with Iron Cores

8.1 M8, Z=10-4Z8

9.6 M8, Z=0

More 2D explosions from 2013

Progenitors from Woosley et al. (2002)

Criticality
parameter forneutrino heating

Progenitors from Woosley & Heger (2007)

Open Questions●●●●●

radialvelocity

Explosions still difficult to obtainin 2D especially for some of theless massive progenitors!
Mass ranges for
successful/failed explosions
compatible with observations?

Eldrige & Smartt

Explosion energies to low?

15 M8 (no transport!)

Do the large-scale sloshingmotions that facilitate explosionsin 2D survive in 3D?
Net effect of 3D helpful or evenharmful? Opinions differ...
2D

entropysnapshots

3D
Hanke et al.
(2012)

Open Questions●●●●●

radialvelocity

Explosions still difficult to obtainin 2D especially for some of theless massive progenitors!

from Nomotoet al. (2003)

Mass ranges for
successful/failed explosions
compatible with observations?
Explosion energies to low?

15 M8 (no transport!)

Do the large-scale sloshingmotions that facilitate explosionsin 2D survive in 3D?
Net effect of 3D helpful or evenharmful? Opinions differ...
2D

entropysnapshots

3D
Hanke et al.
(2012)

Does the SASI Survive in 3D?
Hanke et al. (2013)

shocksurface

velocity around spiral axis

Computed on ~8000 cores of
the CURIE computer (Paris)●●●27 M8Strong sloshing & “spiral” mode in
two 3D models with full transport
SASI looks even “cleaner” than in
2D
Recent parametrized 3D models
provide further confirmation(Couch & O'Connor 2013)

Heating Conditions:
2D vs. 3D●

3D simulations for
11.2M8, 20M8 & 27M8
with multi-grouptransport underway●

No explosions so far!

●Consistent picture:●●Transient phase with
better heating conditions
than in 2D
Failure close to runawaythreshold

The Conundrum●

Ways to obtain robust bubble
expansion in 3D:
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Reduced drag at high resolution –but beware of analogies!
Progenitor asphericities (Couch &Ott 2013)? How large is theeffect?
Magnetic fields? Weak rotation?

Neutrino luminosities, meanenergy & flux factors accurate
within 10%?
●●Rate uncertainties atneutrinospheric densities?
Flavor conversion (multiazimuthal angle instability...)?

Drag coefficient vs. Reynolds number

The Conundrum●

Ways to obtain robust bubble
expansion in 3D:
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●

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Reduced drag at high resolution –but beware of analogies!
Progenitor asphericities (Couch &Ott 2013)? How large is theeffect?
Magnetic fields? Weak rotation?

Neutrino luminosities, meanenergy & flux factors accurate
within 10%?
●●Rate uncertainties atneutrinospheric densities?
Flavor conversion (multiazimuthal angle instability...)?

Drag coefficient vs. Reynolds number

Probing the Supernova Core withNeutrinos
What will observations of a Galactic supernova tell us
about the supernova engine?

Neutrino Signal – Overview●●

Electron neutrino burstafter bounce
Accretion phase:●

Gray-body law for /:
2L~4   R T●

onset ofexplosion

4Additional accretion
contribution
L acc~ G M Ṁ / Rfor e and e●●

e mean energy~neutronstar mass

Signs of the explosion?

27 M8 model, spherical integration of
the total neutrino flux

Can we learn more about the dynamics?
●●

Exploit temporalvariations of the 
signal as fingerprints
of multi-D instabilities!
Exemplary cases:●●

Supernova models as
seen by the IceCube
detector at a distance of
10kpc
No non-linear flavor
conversion & ordinary
mass hierarchy assumed

 flux

25 M8

 fluxDetecting Shock Oscillations
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Sloshing motions result inquasi-periodic andasymmetric neutrino
emission
Sloshing frequency
related to shock andproto-neutron star radius
Modulations survive in 3D(Tamborra et al. 2013)
Detectable in IceCube forup to ~10 kpc
Opportunity to reconstruct
shock trajectory!

Non-exploding 25 M8 modelDetecting Shock Oscillations
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Sloshing motions result inquasi-periodic andasymmetric neutrino
emission
Sloshing frequency
related to shock andproto-neutron star radius
Modulations survive in 3D(Tamborra et al. 2013)
Detectable in IceCube forup to ~10 kpc
Opportunity to reconstruct
shock trajectory!

2
period ∝ r 3/shock
lnr shockr PNS

Signatures of the Explosion●●●Explosion phasecharacterized by slowlychanging large-scaleanisotropies→ emission modulation
periods >20 Hz
Weak explosions:
possible emission spikes
due to “early fallback”

oscillatory“sloshing”

27 M8 explosion modelSignatures of the Explosion●●Explosion phasecharacterized by slowlychanging large-scaleanisotropies→ emission modulation
periods >25ms

radialvelocity

entropy

15 M8 explosion modelSignatures of the Explosion●●Explosion phasecharacterized by slowlychanging large-scaleanisotropies→ emission modulation
periods >25ms

15 M8 explosion modelSignatures of the Explosion●●●Explosion phasecharacterized by slowlychanging large-scaleanisotropies→ emission modulation
periods >25ms
Weak explosions:
possible emission spikes
due to “early fallback”

11.2M8 explosion modelSignatures of the Explosion●●●Explosion phasecharacterized by slowlychanging large-scaleanisotropies→ emission modulation
periods >25ms
Weak explosions:
possible emission spikes
due to “early fallback”

Summary & Outlook●●●The neutrino-driven supernova mechanism works for a host progenitor
models in 2D (from 8.1M8 to 27M8) thanks to GR, good  transport
and improved  rates
But: first self-consistent 3D models with VERTEX fail to explode,though not by far!
Conclusions:●

3D supernova models may bring up more questions than they answer●

Cross-comparisons of model needed to ensure the accuracy of current simulations●●

Don't shirk from questioning the input physics (progenitors, high-density physics,neutrino physics) and current simulation methodology

Direct observations of supernova neutrinos would help a lot to validate
or correct multi-D simulations:●●Time evolution of luminosities & rise of neutrino mean energies reflect theaccretion history (→ progenitor structure)
SASI activity & shock recession/expansion directly reflected in time-frequency
structure of the neutrino signal●Emission modulations at frequencies < 40 Hz mark the onset of the explosion●Early fallback in weak explosions will produce emission spikes