1. 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” http://vega.bac.pku.edu.cn/~rxxu R.X. Xu

2. Quark Stars “Quark Stars” http://vega.bac.pku.edu.cn/~rxxu R.X. Xu I would like to introduce briefly solid bare strange quark stars in this talk. Ref. Xu (astro-ph/0310050) for details.

3. 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” http://vega.bac.pku.edu.cn/~rxxu R.X. Xu

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

5. “Quark Stars” http://vega.bac.pku.edu.cn/~rxxu 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?

6. u What’s QM?  T-dominated Rho 2001  D-dominated “Quark Stars” http://vega.bac.pku.edu.cn/~rxxu R.X. Xu Can a star be composed of QM?

7. “Quark Stars” http://vega.bac.pku.edu.cn/~rxxu R.X. Xu Bowers 2003 Can a star be composed of QM?

8. Weber(1999) J.Phys.G: 25, R195 “Quark Stars” http://vega.bac.pku.edu.cn/~rxxu 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?

9. “Quark Stars” http://vega.bac.pku.edu.cn/~rxxu 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).

10. 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” http://vega.bac.pku.edu.cn/~rxxu R.X. Xu Hadronic instability: Why strange?

11. “Quark Stars” http://vega.bac.pku.edu.cn/~rxxu 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}

12. u Note: strange stars could be... o crusted o bare “Quark Stars” http://vega.bac.pku.edu.cn/~rxxu R.X. Xu Formation & emission: Why bare? Electric field: E ~ 10 17 V/cm

13. “Quark Stars” http://vega.bac.pku.edu.cn/~rxxu 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/0211563).

14. PSR 0943+10Deshpande & Rankin 1999 “Quark Stars” http://vega.bac.pku.edu.cn/~rxxu R.X. Xu u Evidence for bare SSs from radio pulses Formation & emission: Why bare?

15.  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” http://vega.bac.pku.edu.cn/~rxxu R.X. Xu Formation & emission: Why bare?

16.  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” http://vega.bac.pku.edu.cn/~rxxu R.X. Xu Formation & emission: Why bare?

17. “Quark Stars” http://vega.bac.pku.edu.cn/~rxxu 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/0302165) for details.

18. 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” http://vega.bac.pku.edu.cn/~rxxu R.X. Xu Astrophy. appearance: Why solid?

19. u Quark matter with high n B : Fermi gas? à No! The interaction between quarks could cause Fermi-sea unable “Quark Stars” http://vega.bac.pku.edu.cn/~rxxu 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

20. 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” http://vega.bac.pku.edu.cn/~rxxu R.X. Xu Astrophy. appearance: Why solid? u Depth of potential well between n-quark clusters should be in order to solidify quark matter.

21. Xu: astro-ph/0202365, ApJL “Quark Stars” http://vega.bac.pku.edu.cn/~rxxu R.X. Xu u Evidence for solid & bare QSs: featureless spec. Astrophy. appearance: Why solid?

22. NASA News release (2002/4/10): RX J1856 a strange star? Chandra “Quark Stars” http://vega.bac.pku.edu.cn/~rxxu R.X. Xu Astrophy. appearance: Why solid?

23. But we do observe lines: Atomic transition lines? 0.7keV 1.4keV Sanwal et al: astro-ph/0206195 “Quark Stars” http://vega.bac.pku.edu.cn/~rxxu R.X. Xu Xu et al: astro-ph/0207079 Chandra Astrophy. appearance: Why solid?

24. “Solid Quark Stars” http://vega.bac.pku.edu.cn/~rxxu 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?

25. “Solid Quark Stars” http://vega.bac.pku.edu.cn/~rxxu 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  10 18 s -1   > 10 -20 s,  ee ~ 10 -16 s Chandra Astrophy. appearance: Why solid?

26. “Solid Quark Stars” http://vega.bac.pku.edu.cn/~rxxu R.X. Xu Zhu WW (2003) Results:   ~(1.5  5.9)  10 15 s -1 single T  ~ 227eV u Fit the spectr. by solid bare QS model: 1E 1207 XMM-Newton Astrophy. appearance: Why solid?

27. “Solid Quark Stars” http://vega.bac.pku.edu.cn/~rxxu 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?

28. “Quark Stars” http://vega.bac.pku.edu.cn/~rxxu 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

29. “Solid Quark Stars” http://vega.bac.pku.edu.cn/~rxxu 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?

30. 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” http://vega.bac.pku.edu.cn/~rxxu R.X. Xu

31. 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” http://vega.bac.pku.edu.cn/~rxxu R.X. Xu Conclusion

32. 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” http://vega.bac.pku.edu.cn/~rxxu R.X. Xu

33. 谢谢各位！