The role of neutrinos in the evolution and dynamics of neutron stars José A. Pons University of Alicante (SPAIN). Transparent and opaque regimes. NS formation and n role in Supernovae. Neutron stars and proto-NS. Energetic considerations. g-modes and convective instabilities.
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The role of neutrinos in
the evolution and dynamics
of neutron stars
José A. Pons
University of Alicante (SPAIN)
Transparent and opaque regimes.
NS formation and n role in Supernovae.
Neutron stars and proto-NS.
g-modes and convective instabilities.
Long term cooling.
All the previous issues in strange stars.
and opaque regimes
Neutrinos are weakly interacting particles, and in most astrophysical scenarios where they are produced their cross section is so low that neutrinos freely stream through matter.
NS, SS or matter surrounding BH reach supranuclear densities and high temperatures
(T> 1 Mev »1010 K, r»3´1014g/cm3)
In some cases, the mean free path becomes of the order (semitransparent) or even much shorter (opaque) than the scale of the object.
Opaque: proto-NS, proto-SS (T> 5 MeV, l» 1 m)
Semitransparent: SN envelope, NS (T=1-5 MeV).
Transparent: All the rest (T<1 MeV)
Core collapse SN
T»1010 K, r»5´109 g/cm3 ,
Ye» 0.42, s »1-2 (k)
g +(A,Z) --> (A-4,Z-2)+ a
g +a ---> 2 n + 2 p
e- + (A,Z) --> (A,Z-1)+ n
Infall and bounce
neutrinos escape freely
trapping (r>1012 g/cm3 )
(r>3 1014 g/cm3)
n diffusion/emission drives SN dynamics and NS formation
Evolution:The first minute of life
Mantle collapse: 0.1-1 s, heating, compression
Deleptonization: with Joule heating, maximum central T
Cooling: basically thermal neutrinos, from 50 MeV down to 1 MeV
Hot (»10-50 MeV), lepton rich
Large chemical and thermal gradients
Less compact (100 km)
No crust, no superfluid
Cold (T<1 MeV), Ye<0.1
More compact (R=10-15 km)
Solid crust, superfluid interior
Convective instability (Ledoux)
Shear Instability + convection may lead to rigid rotation in a few dynamical periods.
PNS vs. PNS
from collapse from mergers
Hot (»10-50 MeV)
lepton rich YL»0.4
Non isolated !
Moderate diff. rotation
Supramassive only after accretion
T/W = 0.10-0.12
Rotation induced instabilities may appear after diffusion timescale
Less hot (»1-10MeV)
PNS + disk
Probably always supramassive (short lived)
Larger T/W possible ?
Collapses to BH
Long term cooling: n cooling epoch
After T drops below 1 MeV matter is transparent to neutrinos, but this does not mean that n’s become irrelevant. They just escape from the star as they are created. Actually, how a NS cools down during the first million years depends on neutrino emission processes in the core.
Cv dT/dt = -Lg – Ln + H
Fast cooling: direct URCA, quarks, kaon or pion condensate, hyperons …
en= 10N T96 erg/cm3/s; N=24-27
Standard (slow) cooling: modifiedURCA, bremstrahlung
en= 10N T98erg/cm3/s; N=20-21
Superfluidity slows down fast processes.
Neutrinos and bulk viscosity
Bulk viscosity is the dominant mechanism to dissipate energy in pulsating, young NS (T=109-1010 K). Thus, the onset of dynamical instabilities, angular momentum loses, etc. during the first hours of life depend very
much on weak interaction processes.
The same processes that gives the neutrino emissivity will control viscous damping at early times.
EXAMPLE: direct URCA vs. modified URCA
BE CONSISTENT ! If you change your EOS (nuclear interaction, superfluidity, quark deconfinement) change accordingly your interaction processes and thermodynamics.
Absorption-emission ---- Specific heat ---- Bulk viscosity
Scattering ---- Compressibility ---- Shear viscosity