SN Ia: Blown to Smithereens (Röpke and Hillebrandt 2005) Nick Cowan UW Astronomy March 2005
Dec 22, 2015
SN Ia: Blown to Smithereens(Röpke and Hillebrandt 2005)
Nick Cowan
UW Astronomy
March 2005
Nick Cowan
UW Astronomy
March 2005
Type I vs Type II Supernovae
Type I• Thermonuclear
explosion• No hydrogen lines• Silicon feature• WD is blown to
smithereens
Type I• Thermonuclear
explosion• No hydrogen lines• Silicon feature• WD is blown to
smithereens
Type II• Core-collapse• Hydrogen lines• NS or BH is
produced
Type II• Core-collapse• Hydrogen lines• NS or BH is
produced
Observational Constraints
• Ejecta composition and velocity
• Robust explosion mechanism
• Intrinsic variability
• Correlation with progenitor system
• Ejecta composition and velocity
• Robust explosion mechanism
• Intrinsic variability
• Correlation with progenitor system
SN Ia Progenitors
Double-DegeneratesNo hydrogen.They’re common.Very few of them
orbit close enough to collide.
Variety of mass, composition and angular momentum.
Double-DegeneratesNo hydrogen.They’re common.Very few of them
orbit close enough to collide.
Variety of mass, composition and angular momentum.
SN Ia ProgenitorsSingle-Degenerate
Pretty common. 2 ways to blow up! For slow accretion,
Nova explosions remove more mass than is accreted.
For fast accretion, hydrostatic burning of H and He ensues.
Very high accretion rates lead to H-rich envelope.
Single-Degenerate Pretty common. 2 ways to blow up! For slow accretion,
Nova explosions remove more mass than is accreted.
For fast accretion, hydrostatic burning of H and He ensues.
Very high accretion rates lead to H-rich envelope.
SN Ia ProgenitorsAt moderate accretion rates, a degenerate
layer of He might flash, hence compressing the sub-Mchan WD and leading to its explosion.
These types of explosions do not produce the right luminosities, compositions or velocities for the ejecta.
Supersoft X-ray Sources are a proof of principle that WDs can accrete matter in a stable way. (But they’re way less than Mchan)
People may be under-estimating the accretion rate necessary for H & He burning.
Interaction between WD wind and accreting matter may widen the window for SN Ia.
At moderate accretion rates, a degenerate layer of He might flash, hence compressing the sub-Mchan WD and leading to its explosion.
These types of explosions do not produce the right luminosities, compositions or velocities for the ejecta.
Supersoft X-ray Sources are a proof of principle that WDs can accrete matter in a stable way. (But they’re way less than Mchan)
People may be under-estimating the accretion rate necessary for H & He burning.
Interaction between WD wind and accreting matter may widen the window for SN Ia.
OK, fine, let’s just say that Mchan WDs accreting matter are responsible for SN Ia.
How do they blow up?
Nuclear Burning
Subsonic Deflagration
(weak overpressure)• Unstable• Burning occurs at fuel-ash
boundary.• Equilibrium between heat
diffusion and energy generation.
• Fuel slowly heated to Tc.
Subsonic Deflagration
(weak overpressure)• Unstable• Burning occurs at fuel-ash
boundary.• Equilibrium between heat
diffusion and energy generation.
• Fuel slowly heated to Tc.
Supersonic Detonation
(strong overpressure)• Unstable• Burning occurs at fuel-ash
boundary.• Shock heating• Fuel is burned before
having a chance to expand.• Speed depends on .
Supersonic Detonation
(strong overpressure)• Unstable• Burning occurs at fuel-ash
boundary.• Shock heating• Fuel is burned before
having a chance to expand.• Speed depends on .
Rayleigh Taylor Instability
• Re = 1014
• Fasten your seatbelts: we expect turbulence.
• Fuel consumption is determined by flame surface area.
• Re = 1014
• Fasten your seatbelts: we expect turbulence.
• Fuel consumption is determined by flame surface area.
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Kelvin-Helmholtz Instability
• As bubbles of burning matter float up through the star, K-H instability on the surface of the bubbles gives rise to this secondary instability.
• As bubbles of burning matter float up through the star, K-H instability on the surface of the bubbles gives rise to this secondary instability.
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Kolmogorov Spectrum
• Turbulent cascade of motions to smaller length scales.
• Results in turbulent combustion.
• Turbulent cascade of motions to smaller length scales.
• Results in turbulent combustion.
QuickTime™ and aTIFF (Uncompressed) decompressor
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Modeling Explosions
• Need hydrodynamical equations for mass, species, momentum, energy.
• Must include gravity, viscosity, heat and mass diffusion, nuclear energy generation.
• Supplement with ideal gas of nuclei, arbitrarily relativistic degenerate electron gas, radiation, electron-positron pair production and annihilation.
(In other words, its rather tricky.)
• Need hydrodynamical equations for mass, species, momentum, energy.
• Must include gravity, viscosity, heat and mass diffusion, nuclear energy generation.
• Supplement with ideal gas of nuclei, arbitrarily relativistic degenerate electron gas, radiation, electron-positron pair production and annihilation.
(In other words, its rather tricky.)
Details of Current Simulation
• Nuclear Physics Made Simple:
Only consider 5 species: -particles, 12C, 16O, “Mg” and “Ni”.
• 3D grid of size x = 7.9 km• Treat known small-scale effects properly.• Rescale burning rate to reflect unexpected
phenomena like “active turbulent combustion”.
• Nuclear Physics Made Simple:
Only consider 5 species: -particles, 12C, 16O, “Mg” and “Ni”.
• 3D grid of size x = 7.9 km• Treat known small-scale effects properly.• Rescale burning rate to reflect unexpected
phenomena like “active turbulent combustion”.
Results of Simulations
• c3_4 exactly reproduces previous simulations done in 1 octant.
• f1 leads to asymmetric explosions and these are more powerful than their symmetric counterparts.
• Unfortunately, even these mightier explosions are pretty weak by observational standards.
• In the f1 model the ejecta was asymmetric, but still not enough.
• c3_4 exactly reproduces previous simulations done in 1 octant.
• f1 leads to asymmetric explosions and these are more powerful than their symmetric counterparts.
• Unfortunately, even these mightier explosions are pretty weak by observational standards.
• In the f1 model the ejecta was asymmetric, but still not enough.
Conclusions
• Some SN Ia are probably caused by accretion of matter onto a Mchan WD.
• Simulating the explosion of a WD is tricky.• However, taking into account all sorts of
small-scale hydrodynamics and running simulations in 3D for the full star seems to be a step in the right direction.
• Ironically, one of the most readily observable astronomical events is still poorly understood.
• Some SN Ia are probably caused by accretion of matter onto a Mchan WD.
• Simulating the explosion of a WD is tricky.• However, taking into account all sorts of
small-scale hydrodynamics and running simulations in 3D for the full star seems to be a step in the right direction.
• Ironically, one of the most readily observable astronomical events is still poorly understood.