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Theory Group at the University of MilanoAstronuclear Physics of Compact Stars
Pierre M. PizzocheroEJC 2016
Port-Barcarès, 25-30/9/2016
Exploring fundamental physics with Neutron Stars
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Plan of the lecture
• What are neutron stars? Observed properties and inferred extreme physical conditions in their interior.
• Which observations are relevant to fundamentalphysics? Some examples: maximum mass, surfacetemperature, pulsar glitches, gravitational waves, ...
• How extreme is their nuclear structure? From the superfluid crust to the ultra-dense exotic core: expectedproperties of hadronic matter with increasing density.
• Why stars made of neutrons? Effects of strong gravity: neutronization of matter and instability of relativisticdegenerate fermions.
• What could we learn? EoS of dense bulk matter andNN interaction, neutrino emissivity and existence of exoticmatter, nucleon superfluidity, structure of space-time, ...
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optical
Observing neutron stars Supernova Remnant and CCO in Cassiopeia A
X-ray
Central Compact Object
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Observing neutron stars
The Crab: SNR, Pulsar and Pulsar Wind Nebula
opticalComposite IR,V, X
Crab Pulsar
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...and the detectors for neutrinos (SN1987A) and gravitational waves (VIRGO, LIGO)
Earth and space-based telescopes for the electromagnetic spectrum (radio to gamma)
Observing neutron stars
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Observing neutron stars
Pulsars: the most accurate clocks in the Universe
B
B
⍵radiationbeam
The lighthouse model witha rotating magnetic dipole
magnetosphere
Pulsar
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Observing neutron stars The observed zoo of compact objects
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Observing neutron stars Mass determination in binary systems
Lattimer et al.
PSR J1614-2230PSR J0348+0432
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Observing neutron stars
Looking at the x-ray emitting surface of neutron stars
Page et al.
Cas A
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Physical conditions of neutron stars
10
M ~ 1 - 2 M☉R ~ 10 - 15 km⍴av ~1014 - 1015 g/cm3
Tobs ~ 105 - 106 KTint ~ 108 - 109 K⍵ ~ 0.1 - 1000 HzVR/c ~ 0.01 - 0.2 B ~ 108 - 1015 GLcrab ~1038 erg/sGM/Rc2 ~ 0.1 - 0.3
Extreme physical conditionsof the most exotic objects
in the Universe
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The origin of neutron starsGravity-driven evolution: from gaseous nebulae to compact stars
NS
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Neutronization in strong gravity
Electron capturep+e⇄ n
(mn- mp)c2 =1.3MeVmec2 =0.5MeV
Gravity-induced neutronization byrelativistic degenerate electrons
𝜇e+𝜇p =𝜇n𝜇e=cpF ∝ 𝜌1/3
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Chandrasekhar’s gravitational instability
Under relativistic degenerate conditions, gravitationally self-bound spheres of fermions become unstable
𝜖grav ∝ − M/R 𝜖tot∝ (M1/3− M)/R𝜖int =cpF ∝ M1/3/R MCh ~M☉ ~ 1057 nucleons
M<MCh
M>MCh
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Compact stars and hadronic matterProbing the phase diagram of cold and
dense hadronic matter with compact stars
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Compact stars and hadronic matterThe many theoretical facets of compact stars
F. Weber
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Internal structure of neutron stars
𝜌U2-3 𝜌U
0.001𝜌U
Nuclear structure under strong gravity:from the superfluid crust to the exotic core
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Internal structure of neutron starsHow to probe such an exotic system?
D. Page
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Neutron stars and EoS of dense matter
The Nucleon-Nucleoninteraction: the Holy Grailof hadronic physics in the
confined sector
The bridge to astrophysics: the Equation
of State (EoS)of bulk, cold, dense, asymmetric matter
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Neutron stars and EoS of dense matterConstraining the EoS of dense matter: M-R diagram
Lattimer et al.
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Cooling of neutron stars
Neutrino cooling: depend on composition and structure of core and crust ⇒diagnostic tool for NS interior
Standard cooling(low core density)
low mass NS with stiff EoS
Rapid or exotic cooling(high core density)high mass NS or
low mass NS with soft EoS
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Cooling of neutron stars
Cas A: seeing neutrino coolinghappen in a superfluid star
Heinke et al.
The program: cooling as aprobe of NS structure
Yakovlev et al.
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Pulsar glitches and superfluidity
Steady rotational slow-down of Pulsar due to emission of e.m.
and gravitational waves
Glitches are recurrent spin-upsof rotational frequency
(∆𝜔/𝜔 ~10-9- 10-5) withoutexternal causes
Glitches as direct observational evidence of the existence of macroscopic (km-sized) nucleon superfluidity inside NS
Kaspi & Gavrill
𝜏 ≈ 50𝑑
⍵B
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Pulsar glitches and superfluidity
Angular momentum of rotating neutron superfluid is quantized in
parallel array of vortex lines
Vortices in the Inner Crust pin to lattice of exotic nuclei ⇒
angular momentum of neutronsuperfluid is frozen
Collective vortex depinningby hydrodynamical forces
⇓Transfer of vortex angular momentum from superfluid
to star crust ⇓
Glitch in rotational frequency
Microscopic input⇒pinning energy
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Neutron stars and space-time
Compact stars in binary systems: the ultimate general
relativistic flywheel
Testing General Relativity through
high-precision mass measurements
PSR J1614-2230
Demorest et al.
Kramer et al.
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The first evidence for gravitational waves:
the Hulse-Taylorbinary pulsar
Neutron stars and space-time
The first detection: GW150914 (@LIGO)
Abbott et al.
Abbott et al.
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Neutron stars and space-time
The utimate probefor NS interior:
coalescing NS binaries(expected 2017)
Rezzolla et al. Rezzolla et al.
Constraining the EoS of dense matter with GW
short GRB
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The CompStar european network
2008-2013RNP CompStar
http://www.compstar-esf.org
2014-2018COST Action MP1304
Exploring fundamental physics with compact stars
http://compstar.uni-frankfurt.de
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