SN Ia: Blown to Smithereens(Röpke and Hillebrandt 2005)

Nick Cowan

UW Astronomy

March 2005

Nick Cowan

UW Astronomy

March 2005

Outline

• Introduction• Models• Simulations

• Introduction• Models• Simulations

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

Alright, so what kind of astronomical objects can

produce such events?

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.

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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.

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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.

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Bubbly Supernova

Enough of this hydrodynamical mumbo

jumbo, let’s try to simulate one of these things!

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”.

Initial Conditions

f1C3_4

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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.