Constraints on Compact Star Radii and the Equation of State From - PowerPoint PPT Presentation

Constraints on Compact Star Radii and the Equation of State From Gravitational Waves, Pulsars and Supernovae J. M. Lattimer Department of Physics & Astronomy Stony Brook University September 13, 2016 Collaborators: E. Brown (MSU), C. Drischler (TU Darmstadt), K. Hebeler (OSU), D. Page (UNAM), C.J. Pethick (NORDITA), M. Prakash (Ohio U), A. Steiner (UTK), A. Schwenk (TU Darmstadt) Compact Stars and Gravitational Waves Yukawa Institute of Theoretical Physics 1 November, 2016 J. M. Lattimer Constraints on Compact Star Radii and the Equation of State F

Outline ◮ The Dense Matter EOS and Neutron Star Structure ◮ General Causality, Maximum Mass and GR Limits ◮ Neutron Matter and the Nuclear Symmetry Energy ◮ Theoretical and Experimental Constraints on the Symmetry Energy ◮ Extrapolating to High Densities with Piecewise Polytropes ◮ Radius Constraints Without Radius Observations ◮ Universal Relations ◮ Observational Constraints on Radii ◮ Photospheric Radius Expansion Bursts ◮ Thermal Emission from Quiescent Binary Sources ◮ Ultra-Relativistic Neutron Star Binaries ◮ Neutron Star Mergers ◮ Supernova Neutrinos ◮ X-ray Timing of Bursters and Pulsars ◮ Effects of Systematic Uncertainties J. M. Lattimer Constraints on Compact Star Radii and the Equation of State F

Dany Page UNAM J. M. Lattimer Constraints on Compact Star Radii and the Equation of State F

Neutron Star Structure Tolman-Oppenheimer-Volkov equations ( mc 2 + 4 π pr 3 )( ε + p ) dp − G = c 4 r ( r − 2 Gm / c 2 ) dr dm 4 π ε c 2 r 2 = dr ✲ maximum mass p ( ε ) ✲ ✲ ✛ small range of ✲ radii M ( R ) ✲ Equation of State ✛ Observations J. M. Lattimer Constraints on Compact Star Radii and the Equation of State F

Extremal Properties of Neutron Stars ◮ The most compact and massive configurations occur when the low-density equation of state is ”soft” and the high-density equation of state is ”stiff” (Koranda, Stergioulas & Friedman 1997). p = ε − ε o ε o is the only causal limit EOS parameter The TOV solutions scale with ε o ⇒ = soft stiff = ⇐ p = 0 ◦ ε o J. M. Lattimer Constraints on Compact Star Radii and the Equation of State F

Causality + GR Limits and the Maximum Mass A lower limit to the M − R curves for minimally compact EOS = maximum mass sets a ⇒ = lower limit to the ⇒ radius for a given mass. quark stars Similarly, a precision upper limit to R sets s s an upper limit to the maximum mass. R 1 . 4 > 8 . 15 M ⊙ if ∂ε = c 2 ∂ p s M max ≥ 2 . 01 M ⊙ . c 2 = s M max < 2 . 4 M ⊙ if R < 10 . 3 km. If quark matter exists in the interior, the minimum radii are substantially larger. J. M. Lattimer Constraints on Compact Star Radii and the Equation of State F

vanKerkwijk 2010 Romani et al. 2012 Although simple average mass of w.d. companions is 0.23 M ⊙ larger, weighted average is 0.04 M ⊙ smaller Demorest et al. 2010 Fonseca et al. 2016 Antoniadis et al. 2013 Barr et al. 2016 Champion et al. 2008 J. M. Lattimer Constraints on Compact Star Radii and the Equation of State F

Mass-Radius Diagram and Theoretical Constraints GR: R > 2 GM / c 2 P < ∞ : R > (9 / 4) GM / c 2 causality: R > ∼ 2 . 9 GM / c 2 — normal NS — SQS R √ — R ∞ = 1 − 2 GM / Rc 2 J. M. Lattimer Constraints on Compact Star Radii and the Equation of State F

Neutron Star Radii and Nuclear Symmetry Energy ◮ Radii are highly correlated with the neutron star matter pressure around (1 − 2) n s ≃ (0 . 16 − 0 . 32) fm − 3 . (Lattimer & Prakash 2001) ◮ Neutron star matter is nearly purely neutrons, x ∼ 0 . 04. ◮ Nuclear symmetry energy S ( n ) ≡ E ( n , x = 0) − E ( n , 1 / 2) E ( n , x ) ≃ E ( n , 1 / 2) + S 2 ( n )(1 − 2 x ) 2 + . . . � 2 S ( n ) ≃ S 2 ( n ) ≃ S v + L n − n s + K sym � n − n s . . . 3 18 n s n s ◮ S v ∼ 32 MeV; L ∼ 50 MeV from nuclear systematics. ◮ Neutron matter energy and pressure at n s : E ( n s , 0) ≃ S v + E ( n s , 1 / 2) = S v − B ∼ 16 MeV � n 2 ∂ E ( n , 0) � ≃ Ln s ∼ 2 . 7 MeV fm − 3 p ( n s , 0) = ∂ n 3 n s J. M. Lattimer Constraints on Compact Star Radii and the Equation of State F

Theoretical Neutron Matter Calculations Nuclei provide information for matter up to n s . Theoretical studies, beginning from fitting y l n o y low-energy neutron scattering d o b - 2 data and few-body Gandolfi et al. (2015) calculations of light nuclei, can probe higher densities. ◮ Auxiliary Field Diffusion Quantum Monte Carlo (Gandolfi & Carlson) ◮ Chiral Lagrangian Expansion (Drischler, Drischler et al. (2015) Hebeler & Schwenk; Sammarruca et al.) J. M. Lattimer Constraints on Compact Star Radii and the Equation of State F

◮ Chiral Lagrangian calculations of neutron-rich and symmetric matter (Drischler, Hebeler & Schwenk 2016) strongly suggest that the quadratic interpolation E ( n , x ) = E ( n , 1 / 2) + S 2 ( n )(1 − 2 x ) 2 is accurate to within ± 0 . 5 MeV for 0 < n < ∼ (5 / 4) n s for x << 1. In other words � ∂ 2 E ( n , x ) � S ( n ) ≃ S 2 ( n ) ≡ 1 , ∂ x 2 8 x =1 / 2 and E ( n s , 0) = S v + B , p ( n s , 0) = Ln s / 3 . ◮ Experimental constraints on saturation properties (Brown & Schwenk 2014; Kortelainen et al. 2014, Piekarewicz 2010) n s = 0 . 164 ± 0 . 007 fm − 3 , B = − 15 . 9 ± 0 . 4 MeV , K = 240 ± 20 MeV . J. M. Lattimer Constraints on Compact Star Radii and the Equation of State F

Unitary Gas Bounds The assumption that the energy of neutron matter should be larger than the unitary gas, i.e., fermions interacting via pairwise short-range s-wave interaction with an infinite scattering length, which shows a universal behavior, produces strong constraints on the symmetry parameters S v and L (Kolomeitsev et al. 2016). J. M. Lattimer Constraints on Compact Star Radii and the Equation of State F

Nuclear Experimental Constraints The liquid droplet model is a useful frame of reference. Its symmetry parameters S v and S s are related to S v and L : S s ≃ aL � 1 + L − K sym � 12 L + . . . . 6 S v S v r o S v ◮ Symmetry contribution to the binding energy: � − 1 � S s E sym ≃ S v AI 2 1 + . S v A 1 / 3 ◮ Giant Dipole Resonance (dipole polarizability) α D ≃ AR 2 � 1 + 5 � S s . S v A 1 / 3 20 S v 3 ◮ Neutron Skin Thickness � � − 1 � � � 3 2 r o I S s S s 1 + 10 S s r np ≃ 1 + . S v A 1 / 3 S v A 1 / 3 5 3 S v 3 J. M. Lattimer Constraints on Compact Star Radii and the Equation of State F

Theoretical and Experimental Constraints H Chiral Lagrangian G: Quantum Monte Carlo S v − L constraints from Hebeler et al. (2012) Experimental constraints are compatible with unitary gas bounds. Neutron matter constraints are compatible with experimental constraints. J. M. Lattimer Constraints on Compact Star Radii and the Equation of State F

Neutron Star Crusts The evidence is overwhelming that neutron stars have hadronic crusts. ◮ Neutron star cooling, both long term (ages up to millions of years) and transient (days to years), supports the existence of ∼ 0 . 5 − 1 km thick crusts with masses ∼ 0 . 02 − 0 . 05 M ⊙ . ◮ Pulsar glitches are best explained by n 1 S 0 superfluidity, largely confined to the crust, ∆ I / I ∼ 0 . 01 − 0 . 05. The crust EOS, dominated by relativistic degenerate electrons, is very well understood. J. M. Lattimer Constraints on Compact Star Radii and the Equation of State F

Piecewise Polytropes ◦ Crust EOS is known: n < n 0 = 0 . 4 n s . n 3 , p 3 ◦ Read, Lackey, Owen & Friedman (2009) n 2 , p 2 found high-density EOS can be modeled ◦ n 1 , p 1 as piecewise polytropes with 3 segments. nm They found universal break points ◦ n 0 , p 0 ( n 1 ≃ 1 . 85 n s , n 2 ≃ 3 . 7 n s ) optimized fits to a wide family of modeled EOSs. 13.8 14.3 14.8 15.3 15.7 For n 0 < n < n 1 , assume neutron matter EOS. Arbitrarily choose n 3 = 7 . 4 n s . For a given p 1 (or Γ 1 ): 0 < Γ 2 < Γ 2 c or p 1 < p 2 < p 2 c . 0 < Γ 3 < Γ 3 c or p 2 < p 3 < p 3 c . Minimum values of p 2 , p 3 set by M max ; maximum values set by causality. J. M. Lattimer Constraints on Compact Star Radii and the Equation of State F

Causality Even if the EOS becomes acausal at high densities, it may not do so in a neutron star. We automatically reject parameter sets which become acausal for n ≤ n 2 . We consider two model subsets: ◮ Model A: Reject parameter sets that violate causality in the maximum mass star. ◮ Model B: If a parameter set results in causality being violated within the maximum mass star, extrapolate to higher densities assuming c s = c . J. M. Lattimer Constraints on Compact Star Radii and the Equation of State F

Maximum Mass and Causality Constraints 2 p < 3 p Model A: J. M. Lattimer Constraints on Compact Star Radii and the Equation of State F

Radius - p 1 Correlation Model A: J. M. Lattimer Constraints on Compact Star Radii and the Equation of State F

Mass-Radius Constraints from Causality J. M. Lattimer Constraints on Compact Star Radii and the Equation of State F

Other Studies ↑ ¨ Hebeler, Lattimer & Schwenk 2010 Ozel & Freire 2016 J. M. Lattimer Constraints on Compact Star Radii and the Equation of State F

Piecewise-Polytrope R M =1 . 4 Distributions Model A: Model B: J. M. Lattimer Constraints on Compact Star Radii and the Equation of State F