Transcript The outer crust of non-accreeting neutron stars

The outer crust of non-accreting cold
neutron stars
astro-ph/0509325
Stefan Rüster, Jürgen Schaffner-Bielich and Matthias Hempel
Institut für theoretische Physik
J. W. Goethe-Universität, Frankfurt
International Workshop on Astrophysics and Nuclear Structure,
Hirschegg, Austria, January 17, 2006
The outer crust of non-accreting cold
neutron stars
Outline
Introduction
The BPS Model
Used Nuclear Models
Results
Summary and Outlook
Matthias Hempel
The New Physics of Compact Stars
Motivation
results rely on (unknown) masses of neutron-rich isotopes
new experimental data of Audi, Wapstra and Thibault (2003): binding energies
of over 2000 precisely measured nuclei
nuclei present in the crust in reach to be measured by FAIR@GSI, TRIUMF’s
ISAC-II or RIA project
many new theoretical nuclear
models available
grey: known masses
dark-blue: recent measurements
light-blue: accessible at FAIR
Matthias Hempel
Hirschegg, January 17, 2006
Motivation
results rely on (unknown) masses of neutron-rich isotopes
new experimental data of Audi, Wapstra and Thibault (2003): binding energies
of over 2000 precisely measured nuclei
nuclei present in the crust in reach to be measured by FAIR@GSI, TRIUMF’s
ISAC-II or RIA project
many new theoretical nuclear
models available
grey: known masses
dark-blue: recent measurements
light-blue: accessible at FAIR
Matthias Hempel
Hirschegg, January 17, 2006
green: present in outer crust
Motivation
despite negligible mass and small radius (» 300 m) the properties of the crust
are important for observations:
heat transport
electrical resistivity important for evolution of magnetic field
low density EoS of special importance for low mass neutron stars
The BPS Model
nuclei arranged in a bcc lattice within a free e--gas
the total energy density is given by
higher order corrections, not included in BPS
WN mass of the nuclei, binding energy B is the only input parameter
lattice energy WL
electron-screening effects -> deviations of e-distribution from uniformity
Matthias Hempel
Hirschegg, January 17, 2006
The BPS Model
Fermi-Dirac statistics influences the electrostatic interaction between the
electrons:
pressure P is given by
groundstate for given pressure P: minimal b
Z
Matthias Hempel
Hirschegg, January 17, 2006
for variation over A and
The BPS Model
at transition of different equilibrium nuclei (A, Z) ! (A’, Z’)
P and b are equal, but density jump (e, ne , nb, )
Matthias Hempel
Hirschegg, January 17, 2006
Used Nuclear Models - Overview
all models contain data for
A, Z and binding energy B
mass tables taken from
webpages of BRUSLIB and
Dobaczewski, private
communication or generated
inhouse
all Skyrme based mass tables take into account effects from deformations
for spherical relativistic models calculations with and without pairing
deformations included for NL3 and TMA (G.A. Lalazissis, L.S. Geng)
if available, experimental data is used (besides BPS)
Matthias Hempel
Hirschegg, January 17, 2006
Used Nuclear Models – Neutron Driplines
strong shell effects for
relativistic, (non-deformed)
spherical calculations
pairing smoothes the dripline
by smearing of energy levels
deformations give an almost
linear raise and larger Z
good agreement of
deformed calculations
Matthias Hempel
Hirschegg, January 17, 2006
Results – Equation of State
up to  ' 1010 g/cm3
sequences are identical and
rely only on experimental
data!
last common nucleus: 84Se
differences in BPS: 66Ni
and 86Kr were not found
but: EoS shows no
noticeable differences, almost
model-independent
Matthias Hempel
Hirschegg, January 17, 2006
Results – Equation of State
models separate from
each other at high mass
density
about 10% maximum
deviation
jumps in the mass
density as predicted
neutron drip (b=mn)
around =45¢1011g/cm3
Matthias Hempel
Hirschegg, January 17, 2006
Results – Sequences of selected models
five selected most modern
models, all including
deformations
from 56Fe to a sequence of
Nickel isotopes
isotone sequences at magic
numbers N=50 and N=82
again common nuclei at
N=82: 124Mo , 122Zr, 120Sr; due
to precise determination of
dripline in this region
last nucleus lying on the dripline with Z=34-38,
N=82 (N=84 for NL3) for all models
Matthias Hempel
Hirschegg, January 17, 2006
medium super-heavy nucleus
180Xe
Results – Sequences of selected models
without WSc and WEx
heaviest nuclei 180Xe appears
only with screening
only small changes
Matthias Hempel
Hirschegg, January 17, 2006
Results – Sequences of selected models
without lattice (lattice melts at
finite T):
smaller A and Z
isotope sequences
still same endpoint-region
lattice important for
sequence!
Matthias Hempel
Hirschegg, January 17, 2006
Results – Sequences of all models
magic numbers N=50 and
N=82 almost always present
good agreement around
Z=40 and N=82 for all
models
compared to BPS: 66Ni and
86Kr enter in, 76Fe never
occurs
Matthias Hempel
Hirschegg, January 17, 2006
Summary
calculation of the outer crust using the extend BPS model and state-of-the-art
experimental and theoretical mass tables
first investigation for such an enlarged set of nuclear models, including
relativistic ones and effects of deformation
deformations: dripline rises steeper and almost linear
EoS is almost not affected by small differences in the sequence
the sequence follows the magic neutron numbers 50 and 82 until the dripline
is reached
final nucleus pinned down to be around Z=36 and N=82
one medium super-heavy element
Matthias Hempel
Hirschegg, January 17, 2006
Outlook
modelling of the inner crust
new approach: BPS method of the outer crust in coexistence with relativistic
mean-field neutron-gas
extension to finite temperature: suitable for neutron star mergers and corecollapse supernovae
Matthias Hempel
Hirschegg, January 17, 2006
The outer crust of non-accreting cold
neutron stars
astro-ph/0509325
Stefan Rüster, Jürgen Schaffner-Bielich and Matthias Hempel
Institut für theoretische Physik
J. W. Goethe-Universität, Frankfurt
International Workshop on Astrophysics and Nuclear Structure,
Hirschegg, Austria, January 17, 2006