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Fridolin Weber San Diego State University San Diego, California USA IAU Symposium 291 Neutron Stars and Pulsars: Challenges and OpportuniEes aFer 80 years IAU General Assembly XXVIII — 20-­‐31 August 2012, Beijing, China Ø 
Strange Quark Stars versus “Neutron” Stars Ø 
Explore Testable Predic<ons Ø 
q 
Rapid rotaEon q 
Ultra-­‐high electric fields q 
OscillaEons of electron sea q 
Meissner effect (vortex expulsion) q 
Pycnonuclear reacEons Summary Strange Quark Star
Neutron Star
Surface
● Hydrogen/Helium plasma
● Iron nuclei
Outer Crust
● Ions
● Electron gas
Surface
Outer Crust
Inner Crust
● Heavy ions
● Relativistic electron gas
● Superfluid neutrons
Outer Core
● Neutrons, protons
● Electrons, muons
Core
● Electrons
● u,d,s quarks
(color-superconducting)
Radii < 10 km
I
F. Weber (SDSU, 2012)
Radii > 10 km
Masses ~1 to 2 M sun
Inner Core
● Neutrons
● Superconducting protons
● Electrons, muons
● Hyperons (Σ, Λ, Ξ)
● Deltas (Δ)
● Boson (π, K) condensates
● Deconfined (u,d,s) quarks / colorsuperconducting quark matter
Quark Stars* vs “Neutron” Stars Ø  Made enErely of deconfined Ø  May contain deconfined quark maaer only in stellar core quarks and leptons Ø  Self-­‐bound (M ~ R3) Ø  Bound by gravity Ø  Baryon number O(1) < B < 1057 Ø  1056 to 1057 Ø  Electron sea at surface Ø  Absent (super-­‐high electric fields) Ø  May posses outer crusts Ø  Outer crusts Ø  No inner crusts Ø  Inner crusts Ø  Two-­‐parameter stellar sequences Ø  One-­‐parameter stellar sequence *E. Wiaen, Phys. Rev. D 30 (1984) 272; Alcock, Farhi, Olinto, ApJ 310 (1986) 261; Alcock & Olinto, Ann. Rev. Nucl. Part. Sci. 38 (1988) 161; Madsen, Lecture Notes Phys. 516 (1999) 162. Mass-­‐radius relaEonship of neutron stars 10
M/Msun
10
1
Black
holes
1
0
10
−1
10
−2
10
−3
3
Neutron
stars
unstable
equilibrium
White
dwarfs
2 configurations
void
of
compact
stars
Planets
10
0
10
1
10
2
10
R (km)
3
10
4
10
5
Mass-­‐radius relaEonship of neutron stars and strange quark stars bc
d
d
ba
ba
ba
Kepler Period (msec)
RotaEon at Sub-­‐Millisecond Periods Observed masses and rotaEonal periods Neutron stars Strange quark stars Electrically Charged Quark Stars Energy density of electric field is of same order as energy density of quark maaer! T
µ
= (P + ⇤)u uµ + P
ideal fluid 1
µ
+
4⇥
✓
1
µl
F F l+
4⇥
µ
Fkl F kl
◆
GravitaEonal mass Increases by up to 15%. Radius increases by up to 5%. R. Negreiros, FW, M. Malheiro, V. Usov, PRD 80 (2009) 083006
Electrically Charged Quark Stars (cont.) Electron sphere may be differenEally rotaEng! I = (⇥+ ⇥ )
B = const E ( +
)R
Could explain observed magneEc fields of CCOs R. Negreiros, I. Mishustin, S. Schramm, FW, PRD 82 (2010) 103010
Electron sea may perform global (hydrodynamical cyclotron) oscillaEons Frequency spectrum calculated by R. X. Xu et al.* *R. X. Xu, Bastrukov, FW, Yu, Molodtsova, PRD 85 (2012) 023008
AbsorpEon features in spectrum of 1E 1207.4-­‐5209 at 0.7, 1.4 and 2.1 keV* 0.7 keV 1.4 keV 2.1 keV 0.5
1.0
2.0
*G. F. Bignami, P. A. Caraveo, A. De Luca, & S. Mereghen, Nature 423 (2003) 725 Meissner Effect in Quark Stars made of CFL Quark Maaer Vortex expulsion reheats the quark star Cooling of CFL Quark Stars via Vortex Expulsion SGRs/AXPs Negreiros, Niebergal, Ouyed, FW, PRD 81 (2010) 043005
SGRs/AXPs Neutron stars Negreiros, Niebergal, Ouyed, FW, PRD 81 (2010) 043005
Pycnonuclear Reactions
in the Crusts of Neutron
Stars
White dwarf
Neutron star
Neutron star crust
Pycnonuclear reactions
Pycnonuclear Reactions
in the Crusts of Neutron
Stars
White dwarf
Neutron star
Strange quark
matter nuggets
embedded in the
nuclear crust
Strange Quark Matter Nuggets
l 
l 
l 
Nu ~ Nd ~ Ns
A > Amin (~10 to 100)
Charge-to-baryon number ratio depends on whether SQM
is made of
Ø 
“ordinary” quark matter, Z ≈ 0.1 (m150)2 A, or
Ø 
color superconducting quark matter, Z ≈ 0.3 m150 A2/3
Farhi & Jaffe, PRD 30 (1984) 2379; Berger & Jaffe, PRC 35 (1987) 213; Alcock, Farhi, Olinto, ApJ 310 (1986) 261; Madsen, PRL 87 (2001)
172003
Madsen, PRL 87 (2001) 172003; Rajagopal & Wilczek, PRL 86 (2001) 3492; Oertel & Urban PRD 77 (2008) 074015
R = (lattice pairs) x TCoulomb barrier x S x E-1
! ! "#$% " &% '(
) " #& #* $ *& $ **
% $ & % &+'' '(*#("(' ) & ((&
#&# #*
!"#!$%&'()*
+"#,-,'(*.'#'/&*0,
1"#2&33#4526,*
7"#2&33#8,43.(9
:"#.4;,*3,#-,40(/#<&*&2,(,*
!
Gasques et al. PRC 72 (2005) 025806
Yakovlev et al. PRC 74 (2006) 035803
!
6)89#',4(,*,8#'56.'#=6''>#-&((.',
Impact of quark maaer nuggets on pycnonuclear reacEon rates B. Golf, J. Hellmers, F. Weber, PRC 80 (2009) 015804
q 
True ground state of the strong interacEon is not known q 
Key differences between neutron stars and quark stars emerge from the fact that quark stars are self-­‐bound and possess electron seas at their surfaces. q 
Peculiar stellar properEes/phenomena to watch out for: superfast rotaEon, unusually small objects (CCOs), unusually hot objects (SGRs, AGRs), absorpEon features (XDIN, CCOs), superbursts, driFing sub-­‐pulses (R. X. Xu) , quark novae (R. Ouyed), . . . ? q 
Need more observed data (e.g. SkA, FAST)