Quark Stars Renxin Xu ( 徐仁新 ) School of Physics, Peking University Talk presented at CCAST workshop on Dense matter and neutron stars October 22, 2003, Beijing “Quark Stars” R.X. Xu

Quark Stars “Quark Stars” R.X. Xu I would like to introduce briefly solid bare strange quark stars in this talk. Ref. Xu (astro-ph/ ) for details.

SUMMARY  Historical notes  Can a star be composed of QM?  Hadronic stability: Why strange?  Formation & emission: Why bare?  Astrophy. appearance: Why solid?  Conclusion “Quark Stars” R.X. Xu

Landau 1932 Gell-Mann&Zweig Hewish&Bell Gold 1968Quark Star? SQS? What’s the nature of PSRs: NSs? or QSs? Historical notes

“Quark Stars” R.X. Xu Question: Can a star be composed of QM? asymptotic freedom Answer: Possible quark-deconfinement in compact stars should be a straightforward consequence of asymptotic freedom. Can a star be composed of QM?

u What’s QM?  T-dominated Rho 2001  D-dominated “Quark Stars” R.X. Xu Can a star be composed of QM?

“Quark Stars” R.X. Xu Bowers 2003 Can a star be composed of QM?

Weber(1999) J.Phys.G: 25, R195 “Quark Stars” R.X. Xu u Deconfinement occurs probably in NSs Critical density  c ? (4  R 3 /3) -1 ~ 1.5  N Can a star be composed of QM?

“Quark Stars” R.X. Xu Hadronic instability: Why strange? Question: Why are quark stars strange? absolutely stable Answer: The Bodmer-Witten's conjecture! —— Strange quark matter in bulk is absolutely stable, although one can hardly justify it from the first principles (the gauge theory of strong interaction, QCD).

u A simple argument for B -W’s conjecture m u ~ 5 m d ~ 10 m s ~150  =1.5  N  F ~ 400 Farhi & Jaffe (1984) Greiner et al 1998 “Quark Stars” R.X. Xu Hadronic instability: Why strange?

“Quark Stars” R.X. Xu Hadronic instability: Why strange? u Strange stars are QSs with strangeness u Strangeness S is a quantum number for strange quark: S(s) = -1, S(s) = 1 u Strange quarks are actually not strange, we have really a lot of strange virtual quarks in our bodies (protons & neutrons) proton = {uud; uu, dd, ss; g}, neutron = {udd; uu, dd, ss; g}

u Note: strange stars could be... o crusted o bare “Quark Stars” R.X. Xu Formation & emission: Why bare? Electric field: E ~ V/cm

“Quark Stars” R.X. Xu Formation & emission: Why bare? Question: Should quark stars be bare? (1) (2)(3) Answer: Very likely! This is because of (1) detonation, (2) high temperature, and (3) rapid rotation and strong magnetic fields, although a realistic simulation of SNE with a quark phase transition is difficult and does not appear (ref. Xu: astro-ph/ ).

PSR Deshpande & Rankin 1999 “Quark Stars” R.X. Xu u Evidence for bare SSs from radio pulses Formation & emission: Why bare?

 Ruderman-Sutherland (1975) model  Vaccum-gap sparking  V d ~ c (E  B/B 2 )  RS requires: E B >~10keV &  B<0  Difficulties in RS model  Bounding energy of neutron stars: E B <10keV  Why haven’t we observe two distinct kinds of _pulsar radio emission (  B 0)?  Strong complicated multipolar magnetic _fields? (Gil & Mitra, 2001, ApJ, 550, 383) “Quark Stars” R.X. Xu Formation & emission: Why bare?

 Advantages of the bare strange star ideal  E B   for any  B  keeps the RS scenario of vacuum gap sparking  Conclusion  Drifting subpulses are consistent with the RS- _type vacuum gap sparking model.  It is quite natural for bare strange stars, but _requires special conditions for neutron stars. “Quark Stars” R.X. Xu Formation & emission: Why bare?

“Quark Stars” R.X. Xu Astrophy. appearance: Why solid? Question: Are quark stars in a solid state? evidence for solid QSs Answer: This possibility can not be rule out by the first principles; furthermore, competition evidence for solid QSs may exist. Please see Xu (2003, ApJ, L59; or, astro- ph/ ) for details.

u An experimental example: water and ice Temperature-density diagram of pure water E.U. Franck E.U. Franck in: The physics and chemistry of aqueous ionic solutions, p.337 Edited by: M- C. Bellissent- Funel and G.W. Neilson, D. Reidel Publishing Company, 1987 “Quark Stars” R.X. Xu Astrophy. appearance: Why solid?

u Quark matter with high n B : Fermi gas? à No! The interaction between quarks could cause Fermi-sea unable “Quark Stars” R.X. Xu Astrophy. appearance: Why solid? momentum spaceposition space u Condensation: momentum space vs. position space  Space homogeneity: 2SC, CFL, LOFF state  Space inhomogeneity? e.g., lattice structure?  CSC after solidification? u No such ambiguous in electric superconductivity

u n-quark clusters formed in SQM  Multi-quark hadrons (e.g., pentaquark: {uudds} ) decays by str. int. à Decay of multi-quark clusters in QM is forbidden if B-W is correct “Quark Stars” R.X. Xu Astrophy. appearance: Why solid? u Depth of potential well between n-quark clusters should be in order to solidify quark matter.

Xu: astro-ph/ , ApJL “Quark Stars” R.X. Xu u Evidence for solid & bare QSs: featureless spec. Astrophy. appearance: Why solid?

NASA News release (2002/4/10): RX J1856 a strange star? Chandra “Quark Stars” R.X. Xu Astrophy. appearance: Why solid?

But we do observe lines: Atomic transition lines? 0.7keV 1.4keV Sanwal et al: astro-ph/ “Quark Stars” R.X. Xu Xu et al: astro-ph/ Chandra Astrophy. appearance: Why solid?

“Solid Quark Stars” R.X. Xu Bignami et al. Nature, 423 (2003) 725 u Cyclotron absorption: confirmed?  0.7 、 1.4 、 2.1  2.8? XMM-Newton Astrophy. appearance: Why solid?

“Solid Quark Stars” R.X. Xu u Fit the spectr. by solid bare QS model: RX J1856 Zhang, Xu, Zhang (2003) Results: T  = 59.3  0.5 eV R  > 7.4 km   > 1.2  s -1   > s,  ee ~ s Chandra Astrophy. appearance: Why solid?

“Solid Quark Stars” R.X. Xu Zhu WW (2003) Results:   ~(1.5  5.9)  s -1 single T  ~ 227eV u Fit the spectr. by solid bare QS model: 1E 1207 XMM-Newton Astrophy. appearance: Why solid?

“Solid Quark Stars” R.X. Xu u Efforts to understand the spectra in NS models Astrophy. appearance: Why solid?  Turolla, Zane, & Drake 2003: condensation?  1, to be consistant in thermodynamics? 2, can not fit  Ho & Lai 2003: vaccum polarization?  A satisfactory fit of the data is still not possible.  Walter 2003: rapid rotating?  Can RX J1856 become radio quiet (below deathline)? u How to calm down magnetospheric activity? e.g., AXP/SGR-like persistent and burst X-ray emission? radio pulsation?

“Quark Stars” R.X. Xu u Evidence: Glitches and free precession? Astrophy. appearance: Why solid?  Discrepancy: vertex-pinning vs. free preces.  Pinning in precession NSs is much weaker than that predicted by current glitch models  Link 2003: no coexistence of n-vortex and p-flux  Solid strange quark stars:  No difficuty with free precession of radio pulsars  Glitch due to global starquake

“Solid Quark Stars” R.X. Xu u Other astrophysical implications of solid QM  Asteroseismology: r-mode instability?  B-filed origin: ferromagnetism domain?  Cooling T: energy release when solidifying Astrophy. appearance: Why solid?

Conclusion Three issues are challenging the conventional neutron stars models: 1, Drifting subpulses 2, Thermal spectra of NSs 3, Free precession of radio pulsars They may be naturally understood if NSs are actually solid bare SSs! “Quark Stars” R.X. Xu

and in the future...  Phenomenological study for solid quark matter  Ferromagnetic origin of pulsar strong field?  Yang & Luo (1983): Curie T c ~ 100MeV  Tatsumi (2000): spontaneous mag. instab.  Cooling behavior of strange stars “Quark Stars” R.X. Xu Conclusion

SUMMARY  Historical notes  Can a star be composed of QM?  Hadronic stability: Why strange?  Formation & emission: Why bare?  Astrophy. appearance: Why solid?  Conclusion “Quark Stars” R.X. Xu

谢谢各位！