Pair-instability supernovae

Pair-instability supernovae

From Woosley et al. (2002, 2007)

Woosley Lecture 19

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Mass Loss in Very Massive Primordial Stars

• Negligible line-driven winds (mass loss ~ metallicity1/2) (Kudritzki 2002)

• No opacity-driven pulsations (no metals)• Continuum-driven winds likely small contribution• Epsilon mechanism inefficient in metal-free stars

below ~1000 M (Baraffe, Heger & Woosley 2000)from pulsational analysis we estimate upper limits:– 120 solar masses: < 0.2 %– 300 solar masses: < 3.0 %– 500 solar masses: < 5.0 %– 1000 solar masses: < 12.0 %during central hydrogen burning

• Red Super Giant pulsations could lead to significant mass loss during helium burning for stars above ~500 M

8 – 11 M¯: uncertain situation

?

• M < M1 ' 8 M¯: No C ignition

• M > M2 ' 12 M¯: Full nondegenerate burning

• In between: ????

• Degenerate off-centre ignition

• Possibly O-Ne-(Mg?) white dwarfs (after some additional mass loss)

• With sufficient O-Ne core mass: continued burning and core collapse

Pair-instability supernovae

• He burning

• collapse and energy release

• + ! e+ + e-: 1 < 4/3

• Dynamical collapse, bounce, explosive burning (for M < 260 M¯)

• Dynamical collapse directly to black hole (for M > 260 M¯)

Pop. III stars, no mass loss

Possibly observed: SN 2006gy

Smith et al. (2007; ApJ 666, 1116)

Can very massive stars retain their masseven today?

The Pistol Star• Galactic star• Extremely high mass loss rate• Initial mass: 150 (?)• Will die as much less massive object

Pair instability

Helium core mostly convective and radiation a large part of the total pressure.~ 4/3. Contracts and heats up after helium burning. Ignites carbon burning radiatively

Above 1 x 109 K, pair neutrinos accelerate evolution. Contraction continues. Pair concentration increases. Energy goes into rest mass of pairs rather than increasing pressure, < 4/3. Contraction accelerates.

Oxygen and (off-center) carbon burn explosively liberating a large amount of energy. At higher mass silicon burns to 56Ni

The star completely, or partially explodes

Barkat, Rakavy and Sack (1967)

(M> 40 solar masses)

Helium stars, MHe = 2.2 – 8

degeneracy parameter

Nomoto and Hasimoto (1986; Prog. Part. Nucl. Phys. 17, 267)

Pair-Instability Supernovae

Many studies in literature since more than 3 decades, e.g.,Rakavey, Shaviv, & Zinamon (1967)Bond, Anett, & Carr (1984)Glatzel, Fricke, & El Eid (1985)Woosley (1986)

Some recent calculations:Umeda & Nomoto 2001Heger & Woosley 2002

63 M / Me 40

130 > M / Me 95

133   M / Me   63

260 M / Me 130

M 133 Me

M > 260 Me

Pulsational PairSupernovae

Pair instabilitySupernovae

Black holes

Rotation reduces thesemass limits!

Mass loss alters them.¯

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Light curves of pair instability supernovae in their restframe

Compared with a typical SN Ia (red SN 2001el), a Type Iip(blue. SN 1999em) and the hypernova SN 2006gy (green)

Red-shifted light curve of a bright pair-instability SN

Pulsational PairInstability Supernovae

Pulsations

Woosley et al. (2007; Nature 450, 390)

238 million light years away

Smith et al. (2007; ApJ 666, 1116)

Smith et al. (2007; ApJ 666, 1116)

Onset of instability

Woosley et al. (2007; Nature 450, 390)

At end of first pulse

Woosley et al. (2007; Nature 450, 390)

After 2nd pulse

Woosley et al. (2007; Nature 450, 390)

At final point

Woosley et al. (2007; Nature 450, 390)

Velocity and enclosed mass after second mass ejection - 110 solar mass model (74.6 at explosion)

Shock heating

Woosley et al. (2007; Nature 450, 390)

Light curves of the two outbursts (110 solar mass model)

Woosley et al. (2007; Nature 450, 390)

20061999 2012

Absolute R-band magnitudesof the 110 solar mass modelcompared with obsevations of “hypernova” SN 2006gy.

Instabilities will smooththese 1 D calculations.The brighter curve assumedtwice the velocity for all ejecta. (7.2 x 1050 ergbecomes 2.9 x 1051 erg)

Woosley et al. (2007; Nature 450, 390)