Maximum pulsar mass and strange neutron-star cores

Transcription

1 Maximum pulsar mass and strange neutron-star cores P. Haensel Copernicus Astronomical Center (CAMK) Warszawa, Poland PAC2012 Beijing, China October 19-21, 2012 P. Haensel (CAMK) Maximum pulsar mass and neutron-star cores PAC2012, October 19-21, / 12

2 Topics M (obs) max and EOS of dense matter - general Largest precisely measured pulsar mass - brief history M (obs) max and importance of strong interactions Theory of dense matter in a nutshell M NS = 2.0 M : the hyperon puzzle & its proposed solutions Strange NS cores: hyperons vs. quarks Conclusion P. Haensel (CAMK) Maximum pulsar mass and neutron-star cores PAC2012, October 19-21, / 12

3 Maximum measured M NS and EOS of dense matter equation of state (EOS) P = P (ρ), ρ = E/c 2 Oppenheimer & Volkoff (1939) EOS of free Fermi gas of neutrons M max [FFG] = 0.7 M theory might allow us to calculate true M max = M max [P (ρ)] if we knew true EOS observations give {M NS } (ideally: NS mass function... ) Alas, very strong selection effect in the data... observational and evolutionary bias - only binary NS are involved... M max [EOS] > max{m (obs) NS} M (obs) max P. Haensel (CAMK) Maximum pulsar mass and neutron-star cores PAC2012, October 19-21, / 12

4 Highest precisely measured pulsar masses 1975 PSR (NS+NS) Hulse - Taylor binary pulsar 1989: PSR ± M 2003: PSR ± M Weisberg & Taylor (2003) 2008 PSR (NS+MS) 1.67 ± 0.02 M (2011) (99.7%) Freire et al. ±1σ 2010 PSR J (NS+WD) 1.97 ± 0.04 M Demorest et al. (2010) P. Haensel (CAMK) Maximum pulsar mass and neutron-star cores PAC2012, October 19-21, / 12

5 Importance of nuclear (strong) interactions An EOS must satisfy: M max [EOS] > 2.0 M Oppenheimer, Volkoff (1939) M max [FFG] = 0.7 M Today: dominating effect of strong interactions for NS is an (observational) fact! M (obs) max /M max [FFG] > 2.8 P. Haensel (CAMK) Maximum pulsar mass and neutron-star cores PAC2012, October 19-21, / 12

6 EOS of cold dense matter - baryons + leptons Fundamental theory of matter : QCD normal nuclear density ρ g cm 3 Terrestrial nuclear physics: Only three lightest quarks involved, confined into baryons: nuclei, nucleons: u, d; hyperons, hypernuclei: additionally s Many-body theory of nuclear matter = EOS for ρ ρ 0 Effective matter constituents : baryons udd, uds..., leptons e, µ Effective theory : nuclear forces result from exchange of (virtual) mesons qq Basic question: how far this effective theory (hadrons+leptons) can be used in dense cold matter? P. Haensel (CAMK) Maximum pulsar mass and neutron-star cores PAC2012, October 19-21, / 12

7 EOS of cold dense matter - quarks + leptons Two remarkable features of the QCD: confinement of quarks and asymptotic freedom Prediction: for ρ ρ dec cold matter is a plasma of quarks interacting via exchange of gluons. Maybe a small admixture admixture of electrons Both the value of ρ dec and the EOS for ρ > ρ dec are difficult to calculate: matter is a strongly-interacting quark-gluon plasma A solid result of QCD: for mean energy of constituents of dense matter (resulting from Fermi statistics) Λ QCD 1000 MeV the EOS is P 1 3 ρc2 Asymptotic Freedom of the QCD Asymptopia is reached for ρ > g cm 3 - far larger than maximum density reached at centers of massive neutron stars ( g cm 3, only u d s are relevant for NS ) P. Haensel (CAMK) Maximum pulsar mass and neutron-star cores PAC2012, October 19-21, / 12

8 Calculating EOS: Baryons + leptons Examples of successful models from nuclear and hypernuclear physics: Argonne V18(nucleons only), Nijmegen ESC08(nucleons and hyperons) Schulze & Rijken (2011) hyperon puzzle P. Haensel (CAMK) Maximum pulsar mass and neutron-star cores PAC2012, October 19-21, / 12

9 edge of the core at 2ρ 0 density jump at the B-Q phase transition less then 30% P. Haensel (CAMK) Maximum pulsar mass and neutron-star cores PAC2012, October 19-21, / 12 High-density hyperon repulsion Proposed solutions of hyperon puzzle Dexheimer & Schramm (2008), Bednarek et al. (2011), Weissenborn et al. (2011)a Result: thresholds for hyperons unchanged, but smaller populations of hyperons and M max (NH) > 2.0 M Breaking the SU(6) symmetry can further increase M max (NH) (2011)b A stiff superconducting quark core instead of hyperon core Weissenborn et al. Burgio et al. (2008), Blaschke et al. (2011), Haensel & Zdunik 2012 A number of necessary conditions: a v 2 sound /c strong pairing

10 Replacing H-cores by Q-cores and M(R) - 1 µ b (P ) = (E + P )/n b EOS.B of Schulze & Rijken (2011) Examples of M(R) with quark cores: BQ - Q/B stability not imposed BQ - Q/B stability imposed µ (Q) b < µ (B) b reconfinement! P. Haensel (CAMK) Maximum pulsar mass and neutron-star cores PAC2012, October 19-21, / 12

11 Replacing H-cores by Q-cores and M (R) - 2 µb (P ) = (E + P )/nb EOS.B of Bednarek et al. (2012) Examples of M (R) with quark cores: BQ - Q/B stability not imposed BQ - Q/B stability imposed (Q) (B) µb < µb reconfinement! P. Haensel (CAMK) Maximum pulsar mass and neutron-star cores PAC2012, October 19-21, / 12

12 Conclusion The existence of 2M pulsar implies several specific features of cold dense matter: Standard threshold density for hyperons ρ H 2ρ 0 3ρ 0 is acceptable If hyperon core is present - then strong HH repulsion is necessary Quark core in neutron stars: strong overall repulsion between quarks and simultaneously strong attraction (pairing) in specific channels to yield strong superconductivity Critical density for quark-hadron transition should be rather low ρ crit 2ρ 0 3ρ 0 Density jump in hadron-quark transition should not be too large ρ Q /ρ B 1.3 If pulsars with mass larger than 2 M are discovered (e.g., 2.2 M, or 2.4 M,...) then conditions on strange NS core become significantly stronger P. Haensel (CAMK) Maximum pulsar mass and neutron-star cores PAC2012, October 19-21, / 12