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

1. SN Ia: Blown to Smithereens(Röpke and Hillebrandt 2005) Nick Cowan UW Astronomy March 2005

2. Outline • Introduction • Models • Simulations

3. 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 I vs Type II Supernovae

4. Observational Constraints • Ejecta composition and velocity • Robust explosion mechanism • Intrinsic variability • Correlation with progenitor system

5. Alright, so what kind of astronomical objects can produce such events?

6. SN Ia Progenitors Double-Degenerates • No hydrogen. • They’re common. • Very few of them orbit close enough to collide. • Variety of mass, composition and angular momentum.

7. SN Ia Progenitors 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.

8. SN Ia Progenitors • 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.

9. OK, fine, let’s just say that Mchan WDs accreting matter are responsible for SN Ia.How do they blow up?

10. 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 . Nuclear Burning

11. Rayleigh Taylor Instability • Re = 1014 • Fasten your seatbelts: we expect turbulence. • Fuel consumption is determined by flame surface area.

12. 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.

13. Kolmogorov Spectrum • Turbulent cascade of motions to smaller length scales. • Results in turbulent combustion.

14. Bubbly Supernova

15. Enough of this hydrodynamical mumbo jumbo, let’s try to simulate one of these things!

16. 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.)

17. 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”.

18. Initial Conditions C3_4 f1

20. 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.

21. 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.