Welcome from Peking University! “Pulsars and Quark Stars” R. X. Xu Astronomy Dept., School of Physics 4 groups: Galaxies and Cosmology (Prof. Z. H. Fan) Planet nebula physics (Prof. X. W. Liu) AGN and supermassive BHs (Prof. X. B. Wu) Particle astrophysics (Prof. R. X. Xu) KIAA (Kavli inst. for A&A at Peking U.) …

Pulsars & Quark stars Renxin Xu ( 徐仁新 ) School of Physics, Peking University Talk presented at “Workshop on high energy astrophysics” July 25th, Astron. Dept., Nanjing Univ. “Pulsars and Quark Stars” R. X. Xu

Not only is the Universe stranger than we imagine, it is stranger than we can imagine. —— Arthur Eddington What’s the nature of pulsars?  Thought conventionally to be normal neutron stars But no convincing work (either theoretical from first principles or observational) has confirmed Baade – Zwicky ’ s original idea that supernovae produce neutron star  To be quark stars? “Pulsars and Quark Stars” R. X. Xu

Summary  A historical note on pulsars  Obs. hints of quark stars?  Conclusions “Pulsars and Quark Stars” R. X. Xu

It depends on laboratory physics laws to understand astrophysical phenomena! “Pulsars and Quark Stars” R. X. Xu Statistical Laws M-B statistics EoS of Stars BE FD Main-sequent stars Fermion stars

L. Landau S. Chandrasekhar Maybe there are stars with nuclear density after collapse? Degenerate pressure is not omnipotent in standing against the gravitational collapse “Neutron” star R. H. Fowler (1926, soon after FD) A historical note on pulsars “Pulsars and Quark Stars” R. X. Xu

Walter Baade and Fritz Zwicky proposed in 1934 that supernovae could produce cosmic rays and neutron stars … Pulsars (discovered in 1967) could be neutron stars? A. Hewish A historical note on pulsars “Pulsars and Quark Stars” R. X. Xu

Quark? A historical note … M. Gell-Mann (1969) Quarks ?  1950s~1960s: A success in the classification of hadrons discovered in cosmic rays and in accelerators  M. Gell-Mann (1964): Quarks? ---- in mathematical description, rather than in reality.  Zweig (1964): in reality? “Pulsars and Quark Stars” R. X. Xu

Quark? A historical note …  Chinese group (1966)  Experimental evidence for the last one: top quark in 1995

u Experimental evidence for asymptotic freedom A historical note on pulsars “Pulsars and Quark Stars” R. X. Xu

The Nobel prize in Physics (2004) David J. Gross (L) of the University of California at Santa Barbara and his wife (R) Frank Wilczek of the Massachusetts Institute of Technology. H. David Politzer of the California Institute of Technology, Pasadena, California. 1973: SU(3) non-Abelian gauge theory  asymptotic freedom

u What is Quark Matter?  Expected in QCD To be a direct consequence of aympt. freedom A simple QCD phase diagram (Hadron gas) (QGP) A historical note on pulsars “Pulsars and Quark Stars” R. X. Xu

u Pulsars: quark stars?  Ivanenko & Hurdgelaidze (1969)  Itoh (1970)  Bodmer (1971)  Asymptotic freedom  Witten (1984)  1986: Haensel et al.; Alcock et al. A historical note on pulsars “Pulsars and Quark Stars” R. X. Xu

u The structure of normal Neutron stars Heiselberg 2002  Atmosphere  Outer crust  Inner crust  Neutron matter  Core ？ A historical note on pulsars “Pulsars and Quark Stars” R. X. Xu

Neutron Stars v.s. Quark Stars A historical note on pulsars “Pulsars and Quark Stars” R. X. Xu

u Solid Quark Matter?  B T 0 QCD phase? Phase diagram for CO 2 Solid? Liquid? Gas? Hadron QGP A historical note on pulsars “Pulsars and Quark Stars” R. X. Xu

A Solid-quark-matter conjecture Solid QM?  T-dom.  D-dom. Xu 2005 Similar to the superconductivity symmetry broken spontaneously A historical note on pulsars “Pulsars and Quark Stars” R. X. Xu

Radio pulsars Accretion-powered X-ray pulsars X-ray bursts AXP/SGR Dim thermal “Neutron” stars Compac t center objects Members of the family of pulsars … What’s really the nature of pulsars? “Pulsars and Quark Stars” R. X. Xu

The nature of pulsars depends on physics of matter at supranuclear density which is still unknown! supranuclear density which is still unknown! Pulsars Normal neutron stars? Quark stars? (strange or not) Fluid? Solid? { { Historical note on pulsars: Summary “Pulsars and Quark Stars” R. X. Xu

Still a challenging topic … to answer a question arising ~ 80 years ago! “Pulsars and Quark Stars” R. X. Xu Face-to-face … ones with big-names … R. H. Fowler S. Chandrasekhar L. Landau …

Summary  A historical note on pulsars Obs. hints of quark stars? Obs. hints of quark stars?  Conclusions “Pulsars and Quark Stars” R. X. Xu

Observational hints of quark stars?  SNE: bare quark star is better (Chen, Xu 2006)  Non-atomic features? e.g. RXJ1856 (Xu 2002, 2003)  (Bi)drifting subpulse: sparking (Xu…’99, Qiao…’04)  Radio &  -ray profiles: annular gap (Qiao…’04a, …)  Glitches & slow-glitches: (Zhou… 2004, Xu 2006)  … (e.g., free-precessions, low-mass quark stars) “Pulsars and Quark Stars” R. X. Xu

R. Buras, M. Rampp, H.-Th. Janka, K. Kifonidis, 2003, PRL90, “Pulsars and Quark Stars” R. X. Xu

Photon-driven supernovae?  The bare quark-surface helps supernovae?  -luminosity is not limited by the Eddington limit: Due to the chromatic confinement, the thermal luminosity on the quark surface could be as high as  Bare quark surface should be energetic source! “Pulsars and Quark Stars” R. X. Xu

Photon-driven supernovae?  Model of photon-driven supernovae/GRBs Low baryon contamination! “Pulsars and Quark Stars” R. X. Xu

 Nuclear reaction  Non-atomic line in thermal emission Why is the spectrum observation so important? Red shift  Pressure broadening  Observational competition: Who is THE FIRST? Sharp difference: quark matter surface! “Pulsars and Quark Stars” R. X. Xu

Observations: Featureless spectra! Xu (2002) Sharp difference: quark matter surface! “Pulsars and Quark Stars” R. X. Xu

Sharp difference: quark matter surface! NASA News release (2002/4/10): RX J1856 a strange star? Chandra “Pulsars and Quark Stars” R. X. Xu

 Drifting subpulses in radio emission PSR Deshpande & Rankin 1999 (Bi)drifting subpulse : Sparking! “Pulsars and Quark Stars” R. X. Xu

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)? Advantages of the bare strange star idea  E B   for any  B  keeps the RS scenario of vacuum gap sparking “Pulsars and Quark Stars” R. X. Xu (Bi)drifting subpulse : Sparking!

“Pulsars and Quark Stars” R. X. Xu (Bi)drifting subpulse : Sparking! Qiao et al. 2004, ApJL Bi-driftingsubpulses

Summary  A historical note on pulsars  Obs. hints of quark stars? Conclusions Conclusions “Pulsars and Quark Stars” R. X. Xu

Conclusions “Pulsars and Quark Stars” R. X. Xu  Pulsars are not boring giant nuclei!  In addition to test GR, pulsars are also useful to test and to improve the fundamental strong interaction.  Possible evidence for quark stars are proposed.  A solid state of quark matter is suggested.

Thanks a lot and Hope to receive your comment-suggestion Any time “Pulsars and Quark Stars” R. X. Xu

Xu (COSPAR2004), 2006, Adv. in Space Research, 37, 1992 (astro-ph/ ) Wang et al. Nature 440 (2006) (astro-ph/ ) “Pulsars and Quark Stars” R. X. Xu