Probing Extreme Physics with Compact Objects

Transcription

1 Probing Extreme Physics with Compact Objects Dong Lai Department of Astronomy Cornell University

2 Extremes in Astrophysics: Most energetic particles: ev Most energetic photons: ev Highest temperature: Big Bang Best vacuum: ISM: ~1 atom/cm 3 Highest density: neutron stars Strongest magnet: magnetars Strongest gravity: black holes

3 Extremes in Astrophysics: Most energetic particles: ev Most energetic photons: ev Highest temperature: Big Bang Best vacuum: ISM: ~1 atom/cm 3 Highest density: neutron stars Strongest magnet: magnetars Strongest gravity: black holes Focus of this talk: Compact Objects (White Dwarfs, Neutron Stars and Black Holes)

4 A thought experiment: Adding mass (slowly) to Earth 0.1 Radius 10-2 Earth Mass ( )

5 A thought experiment: Adding mass (slowly) to Earth 0.1 Radius 10-2 Earth Mass ( )

6 A thought experiment: Adding mass (slowly) to Earth 0.1 Jupiter Radius 10-2 Earth Mass ( )

7 A thought experiment: Adding mass (slowly) to Earth 0.1 Jupiter Brown Dwarfs Radius 10-2 Earth Mass ( )

8 A thought experiment: Adding mass (slowly) to Earth 0.1 Jupiter Brown Dwarfs Radius 10-2 Earth White Dwarfs Mass ( )

9 A thought experiment: Adding mass (slowly) to Earth 0.1 Jupiter Brown Dwarfs Radius 10-2 Earth White Dwarfs Chandrasekhar mass: Mass ( ) ( )

10 Adding mass to a white dwarf: What happens when its mass exceeds the Chandrasekhar limit? 2000 km White Dwarf km Neutron Star

11 Adding mass to a Neutron Star 20 Radius (km) Mass ( )

12 Adding mass to a Neutron Star 20 Radius (km) Mass ( )

13 Lattimer & Parkash 06

14 Why is there a maximum mass for neutron stars? Force balance in a star: (Newtonian) Pressure balances Gravity <-- M

15 Why is there a maximum mass for neutron stars? Force balance in a star: (Einsteinian) Pressure balances Gravity <-- M, Pressure ===> Tolman-Oppenheimer-Volkoff Limit Tolman-Oppenheimer-Volkoff Equation:

16 Keep adding mass to a neutron star: What happens when its mass exceeds the maximum mass? km Neutron Star Black Hole First demonstrated by Oppenheimer & Snyder (1939)

17 Dark Star Concept: John Michell (1783) Pierre Laplace (1795) M, R Escape velocity: Bold suggestion: Combine Newtonian mechanics/gravity with the particle description of light Although correct answer, derivation wrong

18 Black Hole Concept: Einstein (1915): General Relativity Gravity is not a force, but rather it manifests as curvature of spacetime caused by matter and energy Ensiten field equation: Karl Schwarzschild (1916): The first exact solution to Einstein field equation The horizon radius (Schwarzschild radius): Roy Kerr (1963): Solution for spinning black holes

19 Formation of Compact Objects in Astrophysics

20 White dwarfs evolve from stars with M < 8 Sun ~ NGC 2392, the Eskimo Nebula (HST)

21 Neutron stars evolve from stars with M > 8 Sun ~ Crab nebula Burrows 2000

22 Black Holes evolve from stars with M > 30 (?) Sun ~ Failed bounce/explosion ==> Fall back of stellar material ==> BH formation Collapse of rotating star ==> spinning BH + disk ==> Relativistic jet (?) ==> Gamma-ray bursts W. Zhang et al (2003) H-T Janka

23 Supermassive Black Holes ( Sun) Have been found at the center of most galaxies. Responsible for violent activities associated with AGNs and Quasars (e.g., relativistic jets) Not really compact: mean density with the horizon ~ 1 g/cm 3 for M=10 8 Sun How do supermassive BHs form? --- Merger of smaller black holes in galaxy merger --- Collapse of supermassive stars followed by gas accretion M87

24 Compact Objects Research Today Have become a routine subject of research Not just the objects themselves, but also how they interact/influence their surroundings Associated with extreme phenomena in the universe (e.g. SNe, GRBs) Used as --- an astronomy tool (e.g., expansion rate of the Universe) --- a tool to probe physics under extreme conditions

25 Isolated Neutron Stars have diverse observational manifestations

26 Isolated Neutron Stars Radio pulsars

27 Isolated Neutron Stars Radio pulsars (1 Tesla = 10 4 G) Radiation in all wavelengths: radio, IR, optical, X-rays, Gamma rays Harding & DL 2006

28 Pulse Profiles of 7 Pulsars D. Thompson

29 Pulsar magnetosphere: Region surrounding the neutron star containing relativistic electrons/positrons

30 Pulsar as a unipolar generator Rotation + B field ==> EMF In Pulsars: Charge particles can be acclerated to high energy

31 Pair Cascade in Pulsar Magnetosphere Accelerated particles emit photons Photons decay into e+e- pairs in strong B field

32 D.Page

33 GLAST (launched 6/11/2008) The Gamma-ray Large Area Space Telescope 20 MeV GeV (LAT) (> 10 GeV unexplored) Large field of view (20% of sky for LAT) Large effective area (>5 better than EGRET) ==> Factor of > 30 improvement in sensitivity 5-10 year mission

34 FAST (~2014) The Five-hundred-meter Aperture Spherical Telescope

35 Magnetars Neutron stars powered by superstrong magnetic fields (B>10 14 G) Bursts/flares Giant flares in 3 magnetars 12/04 flare of SGR has E>10 46 erg (>Sun radiates in 10 5 years) Magnetars do not show persistent radio emission Connection with high-b radio pulsars? Radio emission triggered by X-ray outbursts XTE J (Camilo et al. 2006, Kramer et al.2007) 1E =5408 (Camilo et al. 2007)

36 Exotic QED Processes in Magnetar Fields Photon splitting: Vacuum birefringence: (photon propagation affected by B field) e + photon photon e -

37 Plasma+Vacuum ==> Vacuum resonance k z B x y B=10 13 G, E=5 kev, θ B =45 o

38 Thermally Emitting Isolated NSs Perfect X-ray blackbody: RX J Spectral lines detected: (e.g., van Kerkwijk & Kaplan 06; Haberl 06) RXJ ( kev) RXJ (~0.45 kev) RXJ (~0.3 kev) RXJ (~0.3 kev)? RXJ (~0.5 kev)? RBS 1774 (~0.7 kev)? Burwitz et al. (2003)

39 Matter (atoms, molecules, condensed matter) in Strong Magnetic Fields: Critical Field: Strong field: Property of matter is very different from zero-field

40 Atoms and Molecules Strong B field significantly increases the binding energy of atoms. For E.g. at G at G Atoms combine to form molecular chains: E.g. H 2, H 3, H 4,

41 Condensed Matter Chain-chain interactions lead to formation of 3D condensed matter.... Binding energy per cell Zero-pressure density

42 Isolated Neutron Stars Radio pulsars Normal/millisecond pulsars High-B pulsars Gamma-ray pulsars Radio bursters, RRATs etc Magnetars AXPs and SGRs Thermally emitting Isolated NSs Central Compact Objects in SNRs Millisecond Magnetars (central engine of long/soft GRBs?)

43 Reasons for diverse NS Behaviors: Rotation and Magnetic Fields

44 Isolated Black Holes

45 Isolated Black Holes are boring (unobservable)

46 Mass accretion onto Black Holes Stellar-mass BHs in binaries Supermassive BHs in Galaxies

47 Mass accretion onto Black Holes Stellar-mass BHs in binaries Supermassive BHs in Galaxies Accreting gas has angular momentum ==> Accretion disk Friction in the disk ===> emission in X-rays

48 Probing Black Holes Using Radiation from Inner Accreting Disks Measuring the temperature of the inner disk ===> Radius of the inner edge of the disk ===> BH spin (method pioneered by S.Zhang, W.Cui & Chen 1997)

49 Probing Black Holes Using Radiation from Inner Accreting Disks Measuring the temperature of the inner disk ===> Radius of the inner edge of the disk ===> BH spin (method pioneered by S.Zhang, W.Cui & Chen 1997) Measuring the spectral line shape (emitted from inner disk) A. Fabian

50 Probing Black Holes Using Variability of X-ray Emission

51 Quasi-Periodic Oscillations (QPOs) in Black-Hole X-ray Binaries Remillard & McClintock 2006

52 A Possible Origin of QPOs: Oscillations of BH Accretion Disk GR effect produces a cavity in the inner disk, where wave/mode can exist and grow Super-reflection in Disks

53 Merging Binary Neutron Stars/Black Holes

54 Orbital Decay of Hulse-Taylor Pulsar Binary Taylor & Weisberg 2005 Nobel Prize 1993

55 Shibata et al. 2006

56 Merging NSs (NS/BH or NS/NS) as Central Engine of (short/hard) Gamma Ray Bursts

57 Gravitational Waveform: The Last Three minutes

58 Gravitational Waves Warpage of Spacetime Generated by time-dependent quadrupoles Detector response to passage of GWs:

59 Laser Gravitational Wave Interferometer Kip Thorne

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61 LIGO Laser Interferometer Gravitational Observatory

62 Kip Thorne

63 Probing Neutron Star Equation of State Using Gravitational Waves from Binary Merger

64 Summary Compact Objects (Neutron stars and Black Holes) have diverse observational manifestations can be studied in many different ways: radio -- gamma rays, GWs They present a rich set of astrophysics/physics problems Ideal laboratory for probing physics under extreme conditions

65 Thanks!

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67 Neutron Stars/Pulsars as a physics laboratory NS mass measurement (from binary pulsars) Measure radius from thermal emission Rotation rate (sub-ms pulsars?) Measure moment of inertia from double pulsars systems Pulsar Glitches: probe of superfluidity of nucelar matter Precession? NS cooling rate Other important applications: Test GR Probe ISM (electron density and B fields) Probe GW background

68 Probing BH using its Accretion Disk