Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Supernovae Type Ia Explosion Models
Maximilian Wagner
Advised by: Prof. Zingale
March 27, 2015
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Outline
1
Introduction
2
Progenitor Systems and Explosion Models
3
The Merger of White Dwarfs
4
Simulations of Supernovae Due to Mergers
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Type Ia Supernovae and White
Dwarfs
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Why Do We Study Type Ia Supernovae (SNe Ia)?
Homogenity of the majority =⇒ standard candles
⇓
⇓
precise measurement of the
Hubble constant
discovery of the accelerating
universe
But: observation of peculiar events =⇒ uncertainty in exact
mechanism and progenitors
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Classification of SNe
Classification by the spectrum at maximum light:
Figure:
Classification scheme, taken from
http://astronomy.swin.edu.au/c.osmos/S/supernova+classification (03/18/15)
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Light curves of SN Ia
Figure:
Spectra of several SNe Ia at B-band
maximum, see Matheson et al. 2008
Figure:
Light curves of several SNe Ia compared
to numerical calculations, see Scalzo et al. 2014
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Characteristics of (normal) SNe Ia
Thermonuclear explosion of a white dwarf (WD)
⇓
ejecta composition and energy
Spectral lines at maximum light: Si, Ca, Mg, S and O
Production and radioactive decay of 0.5M − 0.9M
56 Ni
⇓
Brightness and light curve
Maximum light: MB ≈ MV ≈ −19.30 ± 0.03 + 5 log(H0 /60)
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Facts About White Dwarfs
Core remnants of low- and intermediate-mass stars
faint =⇒ no Hydrogen burning
TWD = 5000K − 80000K
Most common: Carbon and Oxygen white dwarfs
MWD ∼ M , RWD ∼ RE =⇒ high density
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Physics of White Dwarfs
High density and gravitational pressure
Pauli’s exclusion principle =⇒ electron degeneracy pressure
Chandrasekhar-limit: Completely degenerate electron gas fails
to support WD!
⇓
MWD ≈ 1.38M
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Type Ia Supernovae Explosion Models
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Observational caonstraints on Explosion Models
Spectra =⇒ composition and velocities of the ejecta
Light curves =⇒ amount of produced and decaying
56 Ni
Homogeneity of normal SN Ia =⇒ robustness of the model
Rate of SNe Ia =⇒ must be explained by progenitor system(s)
Fainter events =⇒ parameter governing explosion strength
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
The Most Prominent Scenarios
Chandrasekhar mass explosions
Sub-Chandrasekhar mass explosions
Violent mergers of two white dwarfs
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Chandrasekhar Mass Explosions
Companion star: H/He burning donor
Mechanism:
Accretion until Chandrasekhar limit is reached
⇓
C/O burning (deflagration) and expansion of the wd and
production of intermediate mass elements
⇓
Detonation and production of 56 Ni
Numerical studies: Good agreement with normal SNe Ia but
too rare
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Sub-Chandrasekhar Mass Explosions
Companion star: Helium rich donor
Mechanism
Accretion of He into a He layer
⇓
He detonation
⇓
Shock wave
⇓
Secondary detonation of the WD
Numerical studies: Good agreement of spectra and light
curves, but production of Ti
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Violent Mergers of Two White Dwarfs
Companion star: secondary CO WD
Total mass exceeds Chandrasekhar limit =⇒ explosion after
the merger
Natural explanation of the missing H and He lines
Numerical studies: Very frequent, good agreement with
normal and sub-luminous events
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
The Merger of Two White Dwarfs
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Description of the Merger
Inspiral of the system
Disruption of the
secondary WD
Primary WD accretes the
mass of the secondary
WD
Figure:
Merger proces of a 1.1M and a
0.9M WD, see Hillendbrandt et al. 2013
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Description of the Merger Remnant
Differentially rotating single WD
Surrounded by a Keplerian disc
Heating of the core through
compression
Figure:
Description of the merger
remnant, see Yoon et al. 2007
Cooling of the core through
neutrino emission and thermal
diffusion
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Conditions for SNe Ia
Local peak temperature smaller than critical temperature for
carbon ignition
Sufficiently low mass accretion from the disk
Loss of angular momentum of the core sufficiently slow
compared to cooling
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Simulations of SNe Ia
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Overview of the Numerical Techniques
Reactive equations of hydrodynamics (simple example, 1D):
∂
∂
(ρ, ρv , e, ρλ)+ (ρv , P+ρv 2 , (e+P)v , ρv λ) = (0, ρg , 0, ρR)
∂t
∂x
Coupling to nuclear network
⇓
Ejecta velocities, composition and density
Observables: spectra and light curves
⇓
Radiative transfer code
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Sub-luminous SNe Ia
Nearly equal mass WDs
(MWD ≈ 0.9 M )
M,1 + M,2 > MCh
Ignition at hot spot:
T = 2.9 ∗ 109 K
ρ = 3.8 ∗ 106 g cm−1
Figure:
al. 2010
Evolution of the binary, see Pakmor et
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Comparison of the Synthetic Spectra to SN 2005bl
Figure: Synthetic spectra of the model compared to the observed
spectrum SN 2005bl, see Pakmor et al. 2010
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Synthetic Light Curves
Figure: Synthetic light curves compared to several observed supernovae,
see Pakmor et al. 2010
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Normal SNe Ia
Primary WD: M1 = 1.1M ; secondary WD: M2 = 0.9M
Explosion at hot spot: T = 2.5 ∗ 109 K and
ρ = 2 ∗ 106 g cm−1
Initial conditions: 47.5%C, 50%O and 2.5%Ne
Production of 0.6 M
56 Ni
⇓
and 0.7 M of iron group elements
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Comparison of the Synthetic Sectrum to SN 2003du
Figure: Synthetic spectrum compared to SN 2003du, see Pakmor et al.
2012
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Light Curves
Figure: Comparison of synthetic light curves to several observed normal
SNe Ia, see Pakmor et al. 2012
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Conclusion
Violent merger =⇒ good agreement with observations for
both sub-luminous and normal SNe Ia
Ignition still not completely understood
Different initial condition may lead to a gravitational collapse
Recently observed inhomogeneity =⇒ more than one
progenitor channel
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
References
Hillenbrandt, Kromer, Röpke and Ruiter, Front. Phys., 2013,8(2):
116-143
Pakmor, Kromer, Röpke, Sim, Ruiter, Hillenbrandt, Nature 463,
61-64 (7 January 2010)
Pakmor, Hachinger, Röpke, Hillenbrandt, A&A 528 (2011) A117
Pakmor, Kromer, Taubenberger, Sim, Röpke, Hillenbrandt, The
Astrophysical Journal Letters, 01/2012, 747
Yoon, Podsiadlowski, Rosswog, Mon.Not.R.Astron.Soc. 380,
933948 (2007)
Scalzo et al., MNRAS (May 11, 2014), Vol. 440, 1498-1518
Matheson et al., The Astronomical Journal 135, 1598, 2008
Carrol, Ostlie, An Introduction to Modern Astrophysics, second
edition 2006, Addison-Wesley
Bihari, Schwendemann, Journal of Computational Physics, Volume
154, Issue 1 (1999)
Introduction Progenitor Systems and Explosion Models The Merger of White Dwarfs Simulations of Supernovae Due to Mergers
Thank You!