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

SPIDERStarlib

THE ASTROPHYSICAL JOURNAL

isotopesproject100

White dwarf supernova play a key role in astronomy:

Distance indicators Element factoriesCosmic-ray acceleratorsKinetic energy sourcesBinary star terminus

Green & Yellow - iron and silicon

Blue - high energy electrons

Red - dust

Tycho Supernova Remnant:

Age: - Nov 1572Distance: ~ 8500 ly Diameter: ~ 18 ly (8 arc min) Expansion: ~ 0.0015 ly/yr

Identification of what is exploding is unknown - this is the outstanding mystery in the field.

NASA’s Spitzer, Chandra, & Spain’s Calar Alto

Constellation:Cassiopeia

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.

4000

wavelength in angstroms

5000 6000 7000 8000

silicon II

silicon II

cobalt IImagnesium II

calcium IIiron II

sulfer “W”

oxygen I calcium II

White dwarf supernovae are defined by their spectra: no hydrogen lines and a strong silicon absorption feature.

Kasen 2008

Pereira et al 2013

Near maximum light, spectra are characterized by O-Ca at high velocity (~20k km/s). Late nebular phase spectra are dominated by iron lines.

Pinwheel (M101)

SN 2011fe

0 20 40 60

1010

109

Lum

inosity (

L⊙

)

Time (days since peak)

Optical light curve

56Ni (τ1/2

~ 6 d) +

56Co (τ1/2

~ 77 d)

~0.6 M⊙ of 56Ni

for a typical SNIa

γ-ray escape

Expansion and Diffusion

time scales about equal

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.

Kim et al 1997

Brighter is wider.

-20 0 20 40 60-17

-18

-19

-20

-20 0 20 40 60-17

-18

-19

-20

as measured

light-curve timescale“stretch-factor”corrected

days

MV

- 5

log(

h/65

)

days

MV

- 5

log(

h/65

)

Calan/Tololo SNe Ia

This empirical fact can be used to correct for variations in the peak luminosity to give a standard candle.

After correction, distances are accurate to ≤ 7% !

Surface Temperature (K)

Color

Hot Cool

Blue Red

Dim

Bright

Lum

inos

ity (

Lsun

)

106

10-4

1

Yellow

Warm50,000 6000 3000

1 Msun

Main Sequence

Red Giant

HeliumIgnites

Helium Burning to Carbon

Planetary Nebula:Tosses off Hydrogenand Helium Layers

Runs out ofHelium fuel

Carbon-OxygenWhite Dwarfin 10 billion years

H → He

He

H

HHe

C+O

C core + H envelope DA WDs

SDSS DR1, Madej et al. 2004

Mass [M⊙]

Num

ber o

f sta

rs

100

50

0

0.2 0.4 0.6 0.8 1.0 1.2

Different main-sequence stars make different white dwarfs.

Pluto White Dwarf

Radius: 1185 km

Mass: 0.18 Earth’s

Radius: 1185 km

Mass: 1.37 Sun’s

105 107 109 10110

.5

1

1.5

Central Density g cm-3

Tota

l Mas

s (M

sun)

Ideal

Ferm

i gas + General Relativity

+ Coulomb Corrections

n=3/

2 po

lytro

pe

n=3 polytrope

NeutronStar

WhiteDwarf

Supernova

A white dwarf can only have so much mass.

Single-Degenerate channel Double-Degenerate channel

Mergers:

Collisions:

The relative frequency of these channels is unknown.

Benz et al 1985

The first white dwarf smashes were calculated in 1985:

3D, 5000 particles with nuclear burning done afterwards and approximate thermodynamics.

Bottom line:Tiny amounts of 56Ni produced.

Message:Nothing here, move along.

0.6 + 0.9 Msun

0.6 + 0.6 M⨀, zero impact parameter,x-y plane,temperature.

Raskin et al 2010

2010: 2 million particles with inline burning and realistic thermodynamics.

Message in 2010: Lots of interesting possibilities!

Raskin et al 2010

Equal mass

Equal h

56N

i Yie

ld [M

๏]

00.10.20.30.40.50.6

Particle Count [x1000]0 500 1000 1500 2000

1985result

0.6 + 0.6 M⨀

.4 .6 .8 1 1.20

.5

1

1.5

Mas

s 56

Ni

(M⊙

)

Average White Dwarf Mass (M⊙)

Raskin et al 2010

Kushnir et al 2013

Range of observed 56Ni masses

Average observed mass

Collisions can cover the observed range of 56Ni masses.

Exceptionally bright white dwarf supernova have been interpreted as double-degenerate events.

0.5 1.0 1.5 2.0 2.5 3.0 3.50.0

0.5

1.0

1.5

2.0

Luminosity (1043 erg)

Nic

kel M

ass (

Msu

n)

SN 2009dcSN 2007if

SN 2003fg

SN 2006gz

SN 2005hj

Howell et al 2006

Observations suggest about 5 million white dwarf supernova per year within a redshift of one.

SDSS David Kirkby

Eugene Onegin and Vladimir Lensky’s duel.

Watercolor by Ilya Repin (1899)

An objection to the collision scenario is the perception that such collisions are extremely rare.

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.

σ = πb2 = πR2 1 + vescv

2

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.

3 body problem

e � 0.999999

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.

0 20

Radii of white dwarfs

Head-on

Collision

40 60 80 100 12010

8

109

1010

1011

1012

1013

10

semimajor axis

pericenter

seperation

m1 = m2 = 0.5 M⊙ white dwarf binary

+ m3 = 0.5 M⊙ perturber

14

1015

time (x 1000 yr)

Dis

tance (

cm

)

Katz & Dong 2013

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.

AO Measurements of A-stars, N=121

All binaries

Nu

mb

er

of

bin

arie

s

5

0

5

10

15

50 500 5,000 50,000

Period (years)

Msecondary > 1 M⊙

RV Measurements of red giants in open clusters, N=797

Num

ber o

f Red

Gia

nts

1

10

100

1 2 4 8 16

All Red Giants0.5 < P < 5 yr0.5 < P < 5 yr, Msecondary > 1M⊙

Mprimary (M⊙)

Klein & Katz 2016

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.

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

Advances (plus a little serendipity) over the next decade should enable us to decipher the progenitors of white dwarf supernovae:

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

A successful model starting from a carbon+oxygen white dwarf must make

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