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Supernovae & Neutrinos
Hans Peter Loens
Seminar: Relativistic Heavy-Ion-Physics
February the 2nd 2006
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
Table of Contents
1 What is a Supernova?The PhenomenonSN1987AClassification Of Supernovae
2 Some PreparationsThe Chandrasekhar-MassStellar Burning Stages
3 How A Supernova Explodes (Type-II)Single Steps Of A Type-II SupernovaThe Role Of The NeutrinosWhat We see...What Is Left Behind?
4 What Was Missing? What Needs To Be Improved?
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
The PhenomenonSN1987AClassification Of Supernovae
What Is A Supernova? - Phenomenological Approach
Figure: SN1994D in NGC 4526
Some Facts
huge stellar explosion!
extreme light-radiation (seenext slide!)
luminosity comparable to awhole galaxy
the fate for all stars withmass
M > 8 ·M�
M� = 1.98 · 1033g
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
The PhenomenonSN1987AClassification Of Supernovae
Carrying Away That Much Energy
Extreme Conditions & Characteristics
high temperatures: > 1 MeV ≈ 1.16 · 1010K
high densities: 107 · gcm3 < ρ < 1015 · g
cm3
high luminosity: up to 1010 · L�huge size: radii ∼ 1013m ≈ 1.44 · 104 · R�
Relative Energy Distribution
total energy: ∼ 1053erg ≡ Egrav
(visible) radiation: set as 1 (∼ 1049erg)
kin. energy of the matter: 100 (∼ 1051erg =: 1Bethe)
neutrino energy: 10000 ≡ 99% of total energy ≡ 1053erg=⇒ this is why we concentrate on the neutrinos!
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
The PhenomenonSN1987AClassification Of Supernovae
SN1987A
Figure: SN1987A
SN1987A-Facts
on 24.02.1987
on 23.02.1987⇒ neutrino det.
@GreatMagellanicCloud
distance 50kPc
M ≈ 20 ·M�
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
The PhenomenonSN1987AClassification Of Supernovae
Supernova Classification
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
The Chandrasekhar-MassStellar Burning Stages
The Chandrasekhar-Mass
White Dwarf: fate of a star with M < 8 ·M�
degenerate electron gas!
the degenerate electron gas creates a pressure that ’presses’against the gravitational force=⇒ star only collapses to a minimum size
Definition
The Chandrasekhar-Mass is the largest mass of a star that canwithstand gravitational collapse by degenerate electron pressure:
MCh ≈ 1.457 · (2Ye)2 ·M�
with Ye = # of electrons# of nucleons as the ’electron abundance’
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
Figure: evolution of a star which will end in a Supernova
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
Single Steps Of A Type-II SupernovaThe Role Of The NeutrinosWhat We see...What Is Left Behind?
A Schematic Overview
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
Single Steps Of A Type-II SupernovaThe Role Of The NeutrinosWhat We see...What Is Left Behind?
Pre-Supernova Situation
above table: evolution of a 15 ·M� star
especially note the time scale, temperature, density &neutrino loss
the fusion stops at iron (= Fe has the highest binding energyper nucleon =⇒ no fusion beyond iron!)
’sudden’ stop of fusion in the Fe zone (= no moretemperature output) has dramatic consequences!
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
Single Steps Of A Type-II SupernovaThe Role Of The NeutrinosWhat We see...What Is Left Behind?
The Onion-Structure
Collapse
But if MCore > MCh ≈ 1.4 ·M�=⇒ Fe-core becomes unstable=⇒ core-collapse starts!
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
Single Steps Of A Type-II SupernovaThe Role Of The NeutrinosWhat We see...What Is Left Behind?
Why The Electrons Cannot Withstand
The Processes
There are basically two processes which lead to the core-collapse:
1 Si-burning creates Fe, which is added to the core ⇒ mass ofcore increases
2 electron capture on nuclei:
e− + ANXZ −→ A
N+1XZ−1 + νe
thus Ye changes ⇒ MCh ≈ 1.457 · (2Ye)2 ·M� decreases
EC On Nuclei More Important!
Although the cross-section for EC on nuclei is smaller than on freeprotons, the EC on nuclei is more important because theabundance of free protons is low!
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
Single Steps Of A Type-II SupernovaThe Role Of The NeutrinosWhat We see...What Is Left Behind?
Figure: EC on nuclei dominates relative to EC on protons
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
Single Steps Of A Type-II SupernovaThe Role Of The NeutrinosWhat We see...What Is Left Behind?
What Happens Next?
the core collapses with ≈ 1/4 · cthe core collapses to a hot, dense, neutron-rich sphere=⇒ Proto-Neutron-Star (PNS)
when reaching nuclear-matter densities, the repulsive nuclearforce comes into play
this happens at densities ∼ 1014g/cm3
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
Single Steps Of A Type-II SupernovaThe Role Of The NeutrinosWhat We see...What Is Left Behind?
Collapse-Phase - Properties
Properties/Characteristics
high temperature: reactions nominated by1 strong interaction2 electromagnetic interaction
are in equilibrium ⇒ matter composition in NSE
reactions nominated by weak interaction are NOT inequilibrium
the neutrino interaction with matter must be considered indetail (Boltzmann transport!)
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
Single Steps Of A Type-II SupernovaThe Role Of The NeutrinosWhat We see...What Is Left Behind?
Collapse Phase - Homologous Core
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
Single Steps Of A Type-II SupernovaThe Role Of The NeutrinosWhat We see...What Is Left Behind?
Collapse Phase - Shockwave Formation
@nuclear-matter densities: sudden strong resistance againstgravitation
⇒ sound waves propagate outwards (analogon: vibrations of ahammer hitting an anvil)
these waves stop @sonic-point, while more material keeps onfalling on the core
sound waves collect @sonic-point ⇒ pressure rises there!
=⇒ discontinuous change in velocity=⇒ a shock wave forms which travels outside!
Important
This shock wave is the main ’force’ for the whole explosion. If theshock wave has enough energy to reach the outer burning shells ofthe star, the star will explode!
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
Single Steps Of A Type-II SupernovaThe Role Of The NeutrinosWhat We see...What Is Left Behind?
Core-Collapse Again
Figure: schematic figure of the first stage of the core collapse
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
Single Steps Of A Type-II SupernovaThe Role Of The NeutrinosWhat We see...What Is Left Behind?
The Neutrino-Trapping
With increasing density another important effect comes into play:
Neutrino-Trapping
ρ ∼ 1012g/cm3 the neutrinos are trapped due to elastic scattering!
mean free path: λ = 1ρσ = 1
ρ12·(
108cm([N2/6A]Xnuclei+Xfree neutrons)·E2
ν
)with N = #neutrons
nucleus , A = #nucleonsnucleus , Xi = mass fraction
from this follows: λ ≈ 0.4km - compared to a diffusion lengthD ≈ 8km=⇒ neutrinos cannot leave core in the relevant time-scale
Important
The neutrinos form a Fermi gas!
This effect is very important! Due to the trapping the backward EC comesinto play and thus the EC-rate becomes equilibrated with its backwardreaction!=⇒ Ye can only fall to a minimum value =⇒ thus a significant amount ofelectrons & protons remains!
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
Single Steps Of A Type-II SupernovaThe Role Of The NeutrinosWhat We see...What Is Left Behind?
Neutrino Reactions
elastic scattering:ν + A � ν + A
absorption:νe + (N,Z ) �e− + (N − 1,Z + 1)
ν-e-scattering:ν + e− � ν + e−
inelastic scattering:ν + A � ν ′ + A∗
cross-sections: ∼ E 2ν
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
Single Steps Of A Type-II SupernovaThe Role Of The NeutrinosWhat We see...What Is Left Behind?
Core Bounce
The Bounce
ρ ' (4− 8) · 1014g/cm3
’Point of maximumscrunch’
pressure by the nucleons
the sound-waves traveloutwards=⇒ shock wave
inside the shock: Tincreases
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
Single Steps Of A Type-II SupernovaThe Role Of The NeutrinosWhat We see...What Is Left Behind?
Neutrino Burst
What Does The Shock Wave Do?
The energy of the shock wave is about 1051erg
while travelling outwards, the shock dissociates the Fe-nuclei
The Burst
huge amount of free protons (after shock passage)
huge EC rates (EC on Fe-bound protons much more unlikelythan on free proton - large threshold!)
Neutrinosphere = min. radius where neutrinos are not trapped
sudden neutrino burst from regions beyond theNeutrinosphere!
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
Single Steps Of A Type-II SupernovaThe Role Of The NeutrinosWhat We see...What Is Left Behind?
Neutrino Burst - Graphics
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
Single Steps Of A Type-II SupernovaThe Role Of The NeutrinosWhat We see...What Is Left Behind?
Shock Scenarios
Definition
Depending on the energy of the shock wave, there are differentoutcomes for the shock:
1 prompt shock scenario: the shock has enough energy to reachthe Si-burning layers, there he gains energy (due to theburning) and disrupts the star
2 delayed shock scenario: the shock does not have enoughenergy ⇒ the shock stallssome mechanism(s) transfer(s) energy to the shock for theSupernova to occur!
Unlikely Prompt Shock
Yet, the ’Prompt Shock Scenario’ is unlikely to happen - might onlyhappen in less massive stars - but why?
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
Single Steps Of A Type-II SupernovaThe Role Of The NeutrinosWhat We see...What Is Left Behind?
Shock Stagnation
Due To The Dissociation...
=⇒ shock wave candissociate ≈ 0.6 ·M�core envelope:Menv = Mcore −Mhom
newest estimation:Menv ≈ 1 ·M�
=⇒ shock wave cannot reachthe Si-shell
Accretion Shock
The shock wave stops andmatter from outer regionsfalls through it towards thecore!
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
Single Steps Of A Type-II SupernovaThe Role Of The NeutrinosWhat We see...What Is Left Behind?
Other Neutrino-Flavors
ν-Reactions Behind The Shcok
pair-annihilation: e− + e+ ↔ ν + ν̄neutrino-bremstrahlung: N + N → N + N + ν + ν̄EC/PC: νe + n ↔ p + e− and ν̄e + p ↔ n + e+
µ’s & τ ’s ...
the temperature in the core behind the shock is very high(≈ 1011K )many e−e+-pairs exist (because of the deleptonization theelectron-degeneracy decreases)
rate of energy transfer: r ≈ 1025 · T 9 · (1 + 0.19n) erg/cm3
stwo other flavours besides eletron-flavour: n=2(cannot be created by charged current interaction)Note: Rν different for the neutrino types!f.ex., the matter is neutron-rich: Rν̄e < Rνe
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
Single Steps Of A Type-II SupernovaThe Role Of The NeutrinosWhat We see...What Is Left Behind?
Reviving The Shock
Crucial Reactions
The most important reactions just behind the shock are
νe + n ↔ p + e−
ν̄e + p ↔ n + e+
=⇒ competition: emisson (cooling) VS. absorption (heating)
Definition
due to the different ρ & T profiles, there is a gain-radius Rg :R < Rg : emission dominates!R > Rg : absorption dominates!=⇒ the matter directly behind the stalled shock wave gets heatedby neutrinos!
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
Single Steps Of A Type-II SupernovaThe Role Of The NeutrinosWhat We see...What Is Left Behind?
KABOOOOOM!
The Shock Wave Is Revived!
Within ≈ 0.4s the Neutrinoshave deposited enough energyfor the shock wave to make its
way through the rest of thecore!
Which Model?
Nowadays, it is believed, thatthe delayed shock model isthe ’main’ model forsupernovae.
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
Single Steps Of A Type-II SupernovaThe Role Of The NeutrinosWhat We see...What Is Left Behind?
Supernova Light
the light comes from radioactive decays of nuclei created inthe SN
by scattering with free electrons, these photons arethermalized and radiated away in IR-, UV- & visible-light
main part by 56Ni (0.15 - 0.2 solar masses)
56Ni −→ 56Co in 6 days
56Co −→ 56Fe in 77 days
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
Figure: Massive Stars Remnants; from Heger et al., Astrophy.J. 591
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
What I left out & what are future tasks?
convection: in the newer models, the role of convection is verycrucial: some think that convection has an essential rolebringing hot material to the stalled shock! (needed:huge entropy gradient)
symmetry: usually supernovae do not have a spherical symmetry -this is quite sure, because of the observation that theremnant neutron star gets a kick to a high velocity(102 − 103 km
s ) by the explosion=⇒ the symmetry is now being accepted as veryimportant concerning the simulations!
magnetic fields: might support supernovanuclear physics: much needs to be done, especially the neutrino
energy transportneutrino oscillations: their role is still widely discussedgravitational waves: from supernovae are also being studiedγ-ray bursts: supernovae are thought to be their sources
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos
What is a Supernova?Some Preparations
How A Supernova Explodes (Type-II)What Was Missing? What Needs To Be Improved?
S. Woosley & H.-Th. Janka, The Physics of Core-Collapse Supernovae, Nature Physics 1(2005) 147http://arxiv.org/abs/astro-ph/0601261
Hans A. Bethe, Supernovae, Physics Today Sept. 1990http://www.physicstoday.org/vol-43/iss-9/vol43no9p24_27.pdf
Hans A. Bethe & G. Brown, How a Supernova Explodes, Scientific American 252, 1985
H.-Th. Janka, Astroteilchenphysik in Deutschland - Workshop 2003http://www-ik.fzk.de/workshop/atw/Session7/Janka/janka.pdf
K. Kotake, K. Sato & K. Takahashi, Explosion Mechanism, Neutrino Burst andGravitational Wave in Core-Collapse Supernovaehttp://www.heap.phys.waseda.ac.jp/kkotake/IOP_paper.html
A. Burrows, S. Reddy & T.A. Thompson, Neutrino Opacities in Nuclear Matterhttp://arxiv.org/abs/astro-ph/0404432
K. Langanke, lecture: Nuclear Astrophysics at TU Darmstadt 05/06http://theory.gsi.de/~langanke/
Hans Peter Loens Seminar: Relativistic Heavy-Ion-Physics Supernovae & Neutrinos