From supernovae to neutron stars

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From Supernovae to Neutron Stars
Germán Lugones IAG Universidade de São Paulo
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Classification of Supernovae
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Supernova Paradigm
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• 1) Progenitor Star with M ? 8 MSUN ? onion
  structure ? all stable elements up to iron have
  been synthesized
• 2) Collapse of the iron core when it reaches
  Mchan
• Iron desintegration Neutronization
• 3) Shock wave formation at nuclear saturation
  density
• Collapsing matter rebounds on uncompressible
  nuclear matter
• Shock wave expected to eject the mantle (0.1-0.2
  c).
• In the center just born Neutron Star
• - hot
• - trapped neutrinos

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Sketch of the post collapse stellar core during
the neutrino heating and shock Revival
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• Progenitor star with degenerate iron core
• ? ? 109 g cm-3
• T ? 1010 K
• MFe ? 1.4 MSUN
• RFe ? 6000 km

• Proto-Neutron star
• ? ? nuclear saturation density ?
  3 x 1014 g cm-3
• T ? 30 MeV (1 MeV
  1.16 x 1010 K )
• MPNS ? 1.4 1.7 MSUN due to accretion
• RPNS ? 10 -15 km

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Core collapse supernova Energetics

• Liberated gravitational binding energy of
  neutron star
• EB ? G M2 / RNS ? 3 x 1053 erg ? 17
  MSUN c2
• This shows up as
• 99 neutrinos
• 1 Kinetic energy of explosion (1 of
  this into cosmic rays)
• 0.01 Photons (outshine host galaxy)
• Neutrino Luminosity
• L? ? 3 x 1053 erg / 3 sec ? 3 x 1019 LSUN
  While it lasts, outshines the photon
  luminosity of the entire visible universe.

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1-D Simulations
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Revival of a stalled Supernova shock by neutrino
heating Radial trajectories of equal mass shells
Supernova ejecta
Shock propagation
Hot bubble
Shock formation
Proto Neutron Star
Accretion onto the PNS
Neutrino sphere
- Wilson, Proc. Univ. Illinois, Meeting on
Numerical Astrophysics (1982) - Bethe
Wilson, ApJ 295 (1985) 14
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1- D Failed Explosions
Mezzacappa et al., PRL 86 (2001) 1935
Rampp Janka, ApJ 539 (2000) L33
Spherically symmetric simulations, Newtonian and
General Relativistic, with the most advanced
treatment of neutrino transport do not produce
explosions.
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1-D simulations give failed explosions

• ? In general it is needed an increase in a factor
  2 of the neutrino luminosity from the Proto
  Neutron Star at early times.
• Why do explosions fail
• 1) convection may be important.
• 2) there is physics still missing in the models
  (e.g. current simulations have an oversimplified
  description of neutrino interactions with
  nucleons in the nuclear medium of the neutron
  star).
• 3) Late phases transitions in the proto neutron
  star?

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2-D Simulations
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Shock Wave at 1400 km
Proto Neutron Star
1600 km
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Results of 2-D simulations

• Convection between the PNS and the shock wave
  helps shock revival but it is not sufficient.
• ? Next steps 2-D and 3-D simulations with
  state-of-the-art neutrino transport ? in progress.

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Proto-Neutron Star Evolution
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First stage of PNS evolution Deleptonization ?
Neutrino diffusion deleptonizes the core on
time scales of 50 sec. ? ? R2 /(c?) ? (20
km)2 /(c 1 m) ? 1 sec   ? Temperature increases
due to Joule Heating. Neutrino Transparency
? After 50 seconds the star becomes finally
transparent to neutrinos because ? R. ? At the
end of deleptonization the PNS is still hot. ?
The star has zero net neutrino number and so
thermally produced neutrino pairs dominate the
emission.
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Black hole formation during neutron star birth?

• ?Accretion onto the PNS occurs during the first
  few seconds of evolution. If mass increases
  beyond MCh ? black hole.
• ?BH formation at the end of deleptonization If
  
• MCh(cold, deleptonized PNS) lt MCh(hot,
  lepton rich PNS)
• ? Strange quark matter could be produced at the
  end of deleptonization.
• BH if MCh(SQM star) lt MCh(cold, deleptonized
  PNS)
• ? If the PNS collapses to form a black hole ? the
  ? - emission is believed to cease abruptly.

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The Neutrino Signal from Supernovae and Proto
Neutron Stars
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Supernova Neutrinos Numerical Neutrino Signal
Totani, Sato, Dalhed Wilson, ApJ 496 (1998) 216
NC
CC
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Supernova Neutrinos Observed Neutrino Signal of
SN 1987 A
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Some Conclusions
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Conclusions about Core Collapse Supernovae

• The neutrino-heating mechanism is the favored
  explanation for the explosion.
• However, it is still controversial, (the status
  of the model is not satisfactory)
• Still missing multidimensional simulations with
  an accurate and reliable handling of neutrino
  transport and an up-to-date treatment of the
  input physics (e.g. a better understanding of the
  neutrino interactions in neutron star matter )
• ? It cannot be excluded that the energy for
  supernova explosions is provided by some other
  mechanism,
• - Delayed phase transitions in the proto neutron
  star?

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What do we really know ?
? neutrinos with the expected characteristics are
emitted from collapsed stellar cores ? these
neutrinos carry away the gravitational binding
energy of the nascent neutron star ? neutrino
heating and strong convection must occur behind
the stalled shock. This helps the explosion. ?
analytic studies and numerical simulations find
explosions for a suitable combination of
conditions
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What do we really not know ?

• Why do the supposedly best and most advanced
  spherical models not produce explosions
• Can one trust current multidimensional
  simulations with their greatly simplified and
  approximate treatment of neutrino transport?
• ? How can we explain the large asphericities and
  anisotropies observed in many supernovae?
• What is the reason for the kicks by which pulsars
  are accelerated to average velocities of several
  hundred km/s presumably during the supernova
  explosion?
• You may complete the list

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Phase Transitions in Neutron Stars
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Transition to Quark Matter

• 1) Deconfinement at ? ? ?0
• Neutrons, protons, Hyperons deconfine into their
  constituent quarks
• Timescale of strong interactions. ? 10-23 sec
• In a Proto Neutron Star Tansition must occur
  after a deleptonization timescale ( 10 sec after
  Neutron Star birth) Lugones Benvenuto (1998)
  PRD 083100, Benvenuto Lugones MNRAS (1999) 304,
  L25.
• In an old neutron star the transition is expected
  to happen after mass accretion has increased the
  central density over the deconfinement transition
  density.
• 2) Weak Decay of quarks Releases 4x1053
  ergs and increases the temperature up to 50
  MeV.
• Timescale Weak interactions ? 10-8 sec

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The energy released in neutrinos is sufficient
to give a successful explosion as it increases by
a factor of 2 or more the luminosity of the
central compact object.
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Propagation of the transition

• Begins as a deflagration laminar velocity
  Vlam 104 cm/sec
• Due to the Raleigh-Taylor instability the flame
  rapidly enters a turbulent regime which increases
  the effective surface of burning and accelerates
  the combustion front.
• The magnetic field acts as a surface tension in
  the region where the magnetic field is
  perpendicular to the flame velocity (i. e.
  the equatorial direction) and quenches the
  growing of the RT modes. On the contrary, it has
  no effect when the B-field is parallel to the
  flame velocity (i. e. in the polar direction) .
  The ratio of the polar and equatorial
  velocities is given by

BB B
Vp
B
B
Ve

• Ghezzi, de Gouveia Dal Pino, Horvath, APJ 548,
  193 (2001)

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A potential mechanism for GRB
Lugones, Ghezzi, de Gouveia Dal Pino, Horvath,
APJL (2002) astro-ph / 0207262
In a NS, large asymmetries can be produced even
for moderate values of B !!!
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As a consequence of the asymmetry in the velocity
of the flame, the actual geometry achieved by the
strange quark matter core will resemble a
cylinder orientated in the direction of the
magnetic poles of the neutron star. Since R /
d Vp/Ve 10 we find that typical dimensions
of the cylinder are R10 km d 1km
Neutrino-antineutrino pairs are emitted through
the polar caps
(Fe/Fp 10-2 - 10-4) and annihilate into
electron-positron pairs in a small region just
above the poles.
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• The model explain naturally various features of
  observed GRB
• Beamed emission
• Total energy emitted 1051-1052 ergs

• 3) Timescale of the emission compatible with
  short GRB ( 0.2 sec)

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• Other characteristics depend on the specific
  scenario in which the neutron star is being
  burned,
• ? isolated neutron star
• Low Mass X-ray Binaries
• just born neutron stars in supernova explosions

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Conclusions

• Even after many years of progress and
  development, we are far from a systematic and
  detailed understanding of the core-collapse
  supernova mechanism and the exact nature of
  compact stars . However the subject is much
  richer, the numerical tools are much better, and
  many insights have been won.
• In addition, there are hints at connections
  between some supernovae and some gamma ray
  bursts, stellar mass black hole formation, the
  production of exotic phases of dense matter in
  neutron stars