Neutron Stars. Gradual compression of a stellar iron core trans. [g cm -3 ] CompositionDegen....
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Transcript of Neutron Stars. Gradual compression of a stellar iron core trans. [g cm -3 ] CompositionDegen....
![Page 1: Neutron Stars. Gradual compression of a stellar iron core trans. [g cm -3 ] CompositionDegen. pressure Remarks Iron nuclei; nonrel. free e - nonrel.](https://reader030.fdocuments.net/reader030/viewer/2022032517/56649c9b5503460f94959137/html5/thumbnails/1.jpg)
Neutron Stars
![Page 2: Neutron Stars. Gradual compression of a stellar iron core trans. [g cm -3 ] CompositionDegen. pressure Remarks Iron nuclei; nonrel. free e - nonrel.](https://reader030.fdocuments.net/reader030/viewer/2022032517/56649c9b5503460f94959137/html5/thumbnails/2.jpg)
Gradual compression of a stellar iron coretrans.
[g cm-3]
Composition Degen. pressure
Remarks
Iron nuclei; nonrel. free e- nonrel. e-
~ 106 Electrons become relativ. pFe ~ mec
Iron nuclei; relativ. free e- relativ. e-
~ 109 neutronization Fe ~ (mn – mp - me) c2
p + e- → n + e
Neutron-rich nuclei (6228Ni, 64
28Ni, 6628Ni); rel.
free e-relativ. e-
~ 4x1011 neutron drip n become degen. and stable outside of nuclei
Neutron-rich nuclei; free n; free rel. e- relativ. e-
~4x1012 Neutron degen. pressure dominates
Neutron-rich nuclei; superfluid free n;
rel. free e-
neutron n form bosonic pairs → superfluidity
2x1014 Nuclei dissolve
~ at. nucl. Superfluid free n; superconducting free p; rel. free e-
neutron p form bosonic pairs → superfl. & supercond.
4x1014 pion production
free n, p, e, other elem. particles (, …) neutron
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Radial Structure of a Neutron Star- Heavy Nuclei (56Fe)
- Heavy Nuclei (118Kr); free neutrons; relativistic, degenerate e-
- Superfluid neutrons
![Page 4: Neutron Stars. Gradual compression of a stellar iron core trans. [g cm -3 ] CompositionDegen. pressure Remarks Iron nuclei; nonrel. free e - nonrel.](https://reader030.fdocuments.net/reader030/viewer/2022032517/56649c9b5503460f94959137/html5/thumbnails/4.jpg)
Properties of Neutron Stars
Typical size: R ~ 10 km
Mass: M ~ 1.4 – 3 Msun
Density: ~ 4x1014 g/cm3
→ 1 teaspoon full of NS matter has a mass of ~ 2 billion tons!!!
Rotation periods: ~ a few ms – a few s
Magnetic fields: B ~ 108 – 1015 G
(Atoll sources; ms pulsars)
(magnetars)
![Page 5: Neutron Stars. Gradual compression of a stellar iron core trans. [g cm -3 ] CompositionDegen. pressure Remarks Iron nuclei; nonrel. free e - nonrel.](https://reader030.fdocuments.net/reader030/viewer/2022032517/56649c9b5503460f94959137/html5/thumbnails/5.jpg)
Neutron Star Cooling
Tc ~ 1011 K
Tc ~ 109 K
~ 1 d URCA process:
n → p + e- + e
p + e- → n + e
(non-degenerate n, p)
Tc ~ 108 K
~ 1,000 yr neutrino cooling
Tc ~ 108 K; Teff ~ 106 K
for ~ 10,000 yr
Lph ~ 7x1032 erg/s
max ~ 30 Å (soft X-rays)
![Page 6: Neutron Stars. Gradual compression of a stellar iron core trans. [g cm -3 ] CompositionDegen. pressure Remarks Iron nuclei; nonrel. free e - nonrel.](https://reader030.fdocuments.net/reader030/viewer/2022032517/56649c9b5503460f94959137/html5/thumbnails/6.jpg)
The Lighthouse Model of Pulsars
A Pulsar’s magnetic field has a dipole structure, just like Earth.
Radiation is emitted mostly along the magnetic poles.
Rapid rotation along axis not aligned with magnetic field axis
→ Light house model of pulsars
Pulses are not perfectly regular
→ gradual build-up of average pulse profiles
![Page 7: Neutron Stars. Gradual compression of a stellar iron core trans. [g cm -3 ] CompositionDegen. pressure Remarks Iron nuclei; nonrel. free e - nonrel.](https://reader030.fdocuments.net/reader030/viewer/2022032517/56649c9b5503460f94959137/html5/thumbnails/7.jpg)
Pulsar Emission Models:Polar Cap model
Particle acceleration along magnetic field lines
Synchrotron emission
Curvature radiation
Pair production
Electromagnetic cascades
![Page 8: Neutron Stars. Gradual compression of a stellar iron core trans. [g cm -3 ] CompositionDegen. pressure Remarks Iron nuclei; nonrel. free e - nonrel.](https://reader030.fdocuments.net/reader030/viewer/2022032517/56649c9b5503460f94959137/html5/thumbnails/8.jpg)
Light Cylinder
Pulsar Emission Models:Outer Gap model
Electrons are bound to magnetic fields co-rotating with the pulsar
At a radial distance r = c/co-rotation at the speed of light
→ “light cylinder”
→ Particles ripped off magnetic fields
Synchrotron emission
Curvature radiation
![Page 9: Neutron Stars. Gradual compression of a stellar iron core trans. [g cm -3 ] CompositionDegen. pressure Remarks Iron nuclei; nonrel. free e - nonrel.](https://reader030.fdocuments.net/reader030/viewer/2022032517/56649c9b5503460f94959137/html5/thumbnails/9.jpg)
Pulsar periods and derivatives
Associated with supernova remnants
Mostly in binary systems
![Page 10: Neutron Stars. Gradual compression of a stellar iron core trans. [g cm -3 ] CompositionDegen. pressure Remarks Iron nuclei; nonrel. free e - nonrel.](https://reader030.fdocuments.net/reader030/viewer/2022032517/56649c9b5503460f94959137/html5/thumbnails/10.jpg)
Pulsar periods
Over time, pulsars lose energy and
angular momentum
=> Pulsar rotation is gradually
slowing down.
dP/dt ~ 10-15
Pulsar Glitches:
P/P ~ 10-7 – 10-8
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Energy Loss of Pulsars
From the gradual spin-down of pulsars:
dE/dt = (½ I 2) = I = - (1/6) ┴2 4 r4 c-3 d
dt
┴ ~ B0 r sin
One can estimate the magnetic field of a pulsar as
B0 ≈ 3 x 1019 √PP G
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Images of Pulsars and other Neutron Stars
The vela Pulsar moving through interstellar space
The Crab nebula and
pulsar
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The Crab Pulsar
Remnant of a supernova observed in A.D. 1054
Pulsar wind + jets
![Page 16: Neutron Stars. Gradual compression of a stellar iron core trans. [g cm -3 ] CompositionDegen. pressure Remarks Iron nuclei; nonrel. free e - nonrel.](https://reader030.fdocuments.net/reader030/viewer/2022032517/56649c9b5503460f94959137/html5/thumbnails/16.jpg)
The Crab Pulsar
Visual image X-ray image
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Dispersion of Pulsar Signals
t = (4e2/mec13) DM
DM = ∫ ne(s) ds0
d
DM = Dispersion Measure