Neutron Stars. J.M. Lattimer. Department of Physics & Astronomy Stony Brook University. 25 July 2011

Transcription

1 Department of Physics & Astronomy Stony Brook University 25 July 2011 Computational Explosive Astrophysics Summer School LBL

2 Outline Observed Properties of Structure of Formation and Evolution of Mass Measurements and Implications How Masses of Are Measured Implications of a Large Maximum Mass Neutron Star Radii, the Maximum Mass, and the EOS Nuclear Physics Constraints

3 Observed Properties of Over 1800 known as pulsars A few dozen accreting or quiescent sources in binary systems Less than a dozen isolated neutron stars

4 Pulsars: The Early History Chadwick discovers neutron W. Baade and F. Zwicky predict existence of neutron stars as end products of supernovae Oppenheimer and Volkoff predict mass limit of neutron stars Colgate and White simulate supernovae forming neutron stars Wheeler predicts Crab nebula powered by rotating neutron star C. Schisler discovers pulsing radio sources, including the Crab, with military radar Hewish, Bell, Pilkington, Scott and Collins discover the pulsar PSR , Aug 6. Only Hewish awarded Nobel Prize (1974) Crab pulsar discovered T. Gold identifies pulsars with magnetized, rotating neutron stars The term pulsar first appears in print, in the Daily Telegraph Glitches provide evidence for superfluidity in neutron star Accretion powered X-ray pulsar discovered by Uhuru (not Lt.) Binary pulsar PSR discovered by Hulse and Taylor with orbital decay due to gravitational radiation. Nobel prize First millisecond pulsar, PSR B , discovered by Backer et al Discovery of planets orbiting PSR B , Wolszczan and Frail Prediction of magnetars by Duncan & Thompson.

5 Amazing Facts About Densest objects this side of an event horizon: gcm 3 Four teaspoons on the Earth would weigh as much as the Moon. Largest surface gravity: cm s 2, about g Fastest spinning massive objects known PSR J ad, located in the globular cluster Terzan 5 28,000 light years away, spins at 716 Hz. (33 pulsars have been found in this cluster.) The velocity at this star s equator is c/4. Largest known magnetic field strengths: B = G,Sun=1G. Highest temperature superconductor: T c = 10 billion K The record superconductor on the Earth is mercury thallium barium calcium copper oxide (Hg 12 T l3 Ba 30 Ca 30 Cu 45 O 125 ), at 138 K. Highest temperature since Big Bang: T = 700 billion K Fastest velocity of a massive object in the Galaxy: > 1083 km/s Largest burst of energy in our Galaxy since SN 1604 A burst from magnetar SGR was brighter than the full moon in gamma rays and released more energy in 0.1 s than Sun emits in 100,000 years. It ionized ionosphere to daytime levels. The only place in the universe except for the Big Bang where neutrinos become trapped.

6 Pulsars: Why do they pulse? All models involve the lighthouse effect, in which particles and light are emitted from magnetic poles that are misaligned with the orbital poles (magnetic dipole model). The beam widths are measured in some cases to be several degrees, so we are fortunate to see any given pulsar. It is known that spinning magnetic dipoles can emit energy. Nobody understands in detail how the beaming is accomplished. For the magnetic dipole model, de rot /dt = Ė rot B 2 R 6 P 4 E rot MR 2 P 2 Ė rot MR 2 P 3 Ṗ B R 2 MPṖ > PṖ s Characteristic age τ = P/(2Ṗ) Neutron stars with too small B or ν can not pulse. G From Handbook of Pulsar Astronomy by Lorimer and Kramer

7 The P Ṗ Diagram The H-R Diagram for Pulsars The magnetic field strength and age can be expressed in terms of the period P and the spin-down rate Ṗ: B PṖ, τ P/Ṗ. > > <

8 The Lives of Pulsars

9 Credit: Dany Page, UNAM

10 Proto- and Neutron Star Evolution

11 Model Simulations of Proto- Pons et al. 2000

12 Model Simulations of Proto-

13 Model Signal From Proto-

14 Neutron Star Structure Tolman-Oppenheimer-Volkov equations p(ε) dp dr dm dr = G (m +4πpr 3 )(ε + p) c 2 r(r 2Gm/c 2 ) = 4π ε c 2 r 2 maximum mass M(R)

15 Schematic Nucleonic Energy Density n: numberdensity;x: proton fraction; T :temperature n s 0.16 ± 0.01 fm 3 : nuclear saturation density B 16 ± 1 MeV: saturation binding energy K 220 ± 15 MeV: incompressibility parameter S v 30 ± 6 MeV: bulk symmetry parameter a ± MeV 1 :bulkleveldensityparameter (n, x, T ) = n B + K 1 n 2 n + S v (1 2x) 2 + a 18 n s n s P = n 2 (/n) = n2 K n 1 + S v (1 2x) 2 n 9 n s µ n = n x n x n s = B + K 18 ˆµ = 1 n x = µ n n µ p =4S v (1 2x) n s s = 1 n T =2a ns 2/3 T n ns n 2/3 T 2 + 2an 3 1 nns 1 3 nns +2S v n n s (1 4x 2 ) a 3 ns 2/3 T n ns 2/3 T n

16 Phase Instabilities

17 The Uncertain Nuclear Force The density dependence of E sym(n) =E neutrons(n) E symmetric (n) iscrucialbut poorly constrained. The skewness, 3 E/ n 3,isalsouncertain. == E sym(n) = Skewness C. Fuchs, H.H. Wolter, EPJA 30(2006) 5

18 The Uncertain E sym (n) C. Fuchs, H.H. Wolter, EPJA 30(2006) 5