Download Smashing White Dwarfs

A hypothesis or theory is clear, decisive, and positive, but it is believed by no one but the person who created it.
Experimental findings, on the other hand, are messy, inexact things, which are believed by everyone except the person who did that work.
Harlow Shapley
Through Rugged Ways to the Stars
Smashing White Dwarfs: Book One of the Supernovae Trilogy
Frank Timmes
SPIDER
Starlib
100 isotopes
project
THE ASTROPHYSICAL JOURNAL
White dwarf supernova play a key role in astronomy:
Distance indicators Element factories
Cosmic-ray accelerators
Kinetic energy sources
Binary star terminus
Identification of what is exploding is unknown - this is the outstanding mystery in the field.
Tycho Supernova Remnant:
Age:
- Nov 1572
Distance: ~ 8500 ly
Diameter: ~ 18 ly (8 arc min)
Expansion: ~ 0.0015 ly/yr
Blue - high energy electrons
Constellation:
Cassiopeia
Green & Yellow - iron and silicon
Red - dust
NASA’s Spitzer, Chandra, & Spain’s Calar Alto
Several observational characteristics help in the hunt for the progenitors of the explosions:
1) About 90% of all white dwarf supernova form a
homogeneous class in terms of their spectra and
light curves.
White dwarf supernovae are defined by their spectra: no hydrogen lines and a strong silicon absorption feature.
silicon II
cobalt II
magnesium II
sulfer “W”
iron II
calcium II
silicon II
4000
5000
6000
oxygen I
7000
wavelength in angstroms
calcium II
8000
Kasen 2008
Pinwheel (M101)
SN 2011fe
Near maximum light, spectra
are characterized by O-Ca at
high velocity (~20k km/s). Late nebular phase spectra
are dominated by iron lines.
Pereira et al 2013
Expansion and Diffusion
time scales about equal
Luminosity (L⊙)
1010
Optical light curve
56Ni (τ ~ 6 d) +
1/2
56Co (τ ~ 77 d)
1/2
~0.6 M⊙ of 56Ni
for a typical SNIa
γ-ray escape
109
0
20
40
Time (days since peak)
60
Several observational characteristics help in the hunt for the progenitors of the explosions:
1) About 90% of all white dwarf supernova form a
homogeneous class in terms of their spectra and
light curves.
2) Correlations between different observables, such as the peak luminosity and width of the light curve.
-20
Brighter is wider.
MV - 5 log(h/65)
as measured
This empirical fact can
be used to correct for
variations in the peak
luminosity to give a
standard candle.
-18
Calan/Tololo SNe Ia
-17
-20
0
20
40
60
days
-20
light-curve timescale
“stretch-factor”corrected
MV - 5 log(h/65)
After correction,
distances are
accurate to ≤ 7% !
-19
-19
-18
-17
-20
Kim et al 1997
0
20
days
40
60
106
Planetary Nebula:
Tosses off Hydrogen
and Helium Layers
Bright
Runs out of
Helium fuel
He
C+O
H
Red Giant
Luminosity (Lsun)
He
Main Sequence
Helium
Ignites
1 Msun
1
10-4
Helium Burning
to Carbon
Carbon-Oxygen
White Dwarf
in 10 billion years
H → He
Dim
Hot
50,000
Blue
Surface Temperature (K)
Color
Cool
Warm
6000
3000
Yellow
Red
H
Different main-sequence stars make different white dwarfs.
C core + H envelope DA WDs
SDSS DR1, Madej et al. 2004
Number of stars
100
50
0
0.2
0.4
0.6
0.8
Mass [M⊙]
1.0
1.2
Pluto
White Dwarf
Radius: 1185 km
Radius: 1185 km
Mass: 0.18 Earth’s
Mass: 1.37 Sun’s
A white dwarf can only have so much mass.
1.5
Fe
rm
ig
Id
ea
l
pe
2 po
lytro
1
+ General Relativity
+ Coulomb Corrections
n=3/
Total Mass (Msun )
as
n=3 polytrope
Neutron
White
Star
Dwarf
Supernova
.5
0
5
10
7
10
10
-3
Central Density g cm
9
10
11
Single-Degenerate channel
Double-Degenerate channel
Mergers:
Collisions:
The relative frequency of
these channels is unknown.
The first white dwarf smashes were
calculated in 1985:
0.6 + 0.9 Msun
3D, 5000 particles with nuclear
burning done afterwards and
approximate thermodynamics.
Bottom line:
Tiny amounts of 56Ni produced.
Message:
Nothing here, move along.
Benz et al 1985
2010: 2 million particles with inline burning
and realistic thermodynamics.
0.6 + 0.6 M⨀,
zero impact
parameter,
x-y plane,
temperature.
Raskin et al 2010
56
Ni Yield [M๏]
Message in 2010: Lots of interesting possibilities!
0.6
0.5
0.4
0.3
0.2
0.1
0
0.6 + 0.6 M⨀
Equal mass
Equal h
1985
result
0
Raskin et al 2010
500
1000
1500
Particle Count [x1000]
2000
Collisions can cover the observed range of 56Ni masses.
Mass
56
Ni (M⊙)
1.5
Range of observed
56
Ni masses
1
Average
observed
mass
.5
Raskin et al 2010
Kushnir et al 2013
0
.4
.6
.8
1
Average White Dwarf Mass (M⊙)
1.2
Exceptionally bright white dwarf supernova have
been interpreted as double-degenerate events.
2.0
SN 2009dc
SN 2007if
Nickel Mass (Msun)
1.5
SN 2003fg
SN 2006gz
1.0
SN 2005hj
0.5
Howell et al 2006
0.0
0.5
1.0
1.5
2.0
2.5
Luminosity (1043 erg)
3.0
3.5
Observations suggest about 5 million white dwarf
supernova per year within a redshift of one.
SDSS
David Kirkby
An objection to the collision scenario is the perception that such collisions are extremely rare.
Eugene Onegin
and Vladimir
Lensky’s duel.
Watercolor by Ilya Repin (1899)
Collisions have been believed to predominantly occur in dense
stellar environments, such as cores of globular clusters.
Even accounting for gravitational focusing, the collision rate is
~5000 white dwarf supernovae per year within a redshift of one.
2
σ = πb = πR
2
1+
vesc 2
v
Wait! There is a 3rd body in this duel.
Eugene Onegin
and Vladimir
Lensky’s duel.
Watercolor by Ilya Repin (1899)
Hierarchical triple star systems with white dwarf binary
orbital separations of 1-300 AU are known to exist.
The white dwarf binary’s ellipticity can be driven to large values in
a triple star system because ellipticity can be traded for inclination
in the conservation of angular momentum
Lz =
1
e2 cos(i)
in Kozai-Lidov oscillations.
e � 0.999999
3 body problem
15
10
14
m1 = m2 = 0.5 M⊙ white dwarf binary
+ m3 = 0.5 M⊙ perturber
semimajor axis
10
13
Distance (cm)
10
12
10
11
10
10
pericenter
seperation
10
9
Radii of white dwarfs
10
Head-on
Collision
Katz & Dong 2013
8
10
0
20
40
60
80
time (x 1000 yr)
100
120
White dwarfs in a triple star system have a ~3% chance of
experiencing a collision within 5 billion years.
If ~20% of white dwarfs are in triplets, the calculated
supernova rate is about the same as the inferred rate.
15-20 % of 1M⊙ ≤ M ≤ 8M⊙ stars with a M > 1M⊙
companion makes the collision scenario dominant.
RV Measurements of red giants in open clusters, N=797
All binaries
Msecondary > 1 M⊙
15
All Red Giants
0.5 < P < 5 yr
0.5 < P < 5 yr, Msecondary > 1M⊙
Number of Red Giants
Number of binaries
AO Measurements of A-stars, N=121
10
5
100
10
0
5
50
500
Period (years)
5,000
50,000
1
1
2
4
Mprimary (M⊙)
8
Klein & Katz 2016
16
Prediction: GAIA will find ~10 new wide orbit
double degenerates within 20 pc from the Sun.
This puts a strong constraint on the “triple-assisted”
collision model for white dwarf supernovae.
Advances (plus a little serendipity) over the next decade should
enable us to decipher the progenitors of white dwarf supernovae:
1) Silicon, Sulfur, Calcium ratios
2) Unburned carbon and oxygen
3) Tidal tails
4) Sufficient number of binary WDs
5) Early gamma-rays
6) Narrow hydrogen emission or absorption
7) Circumstellar interaction in radio or x-rays
8) Gravitational wave signatures
9) Frequency as a function of redshift
A successful model starting from a carbon+oxygen white dwarf must make
0.1 - 1.0 M☉ 56Ni
for the light curve
0.2 - 0.4 M☉ Si, S, Ar, Ca
for the spectrum
< 0.1 M☉ 54Fe + 58Ni
for the nucleosynthesis
Allow for some diversity
for the population
Raskin et al 2010
0.8 + 0.6 M⨀,
zero impact parameter,
density
Raskin et al 2010
0.8 + 0.6 M⨀,
zero impact parameter,
density, zoomed
Raskin et al 2010