Probing Extreme Physics with Compact Objectshosting.astro.cornell.edu/~dong/talks/ustc.pdf•...
Transcript of Probing Extreme Physics with Compact Objectshosting.astro.cornell.edu/~dong/talks/ustc.pdf•...
Probing Extreme Physics withProbing Extreme Physics with
Compact ObjectsCompact Objects
Dong Lai
Department of AstronomyCornell University
“Extremes” in Astrophysics:
• Most energetic particles: 1020 eV• Most energetic photons: 1014 eV• Highest temperature: Big Bang• Best vacuum: ISM: ~1 atom/cm3
• Highest density: neutron stars• Strongest magnet: magnetars• Strongest gravity: black holes• •
“Extremes” in Astrophysics:
• Most energetic particles: 1020 eV• Most energetic photons: 1014 eV• Highest temperature: Big Bang• Best vacuum: ISM: ~1 atom/cm3
• Highest density: neutron stars• Strongest magnet: magnetars• Strongest gravity: black holes• • Focus of this talk: Compact Objects (White Dwarfs, Neutron Stars and Black Holes)
A thought experiment: Adding mass (slowly) to Earth …
Mass ( )
Radius
Earth
10-6 10-3 1
10-2
0.1
A thought experiment: Adding mass (slowly) to Earth …
Mass ( )
Radius
Earth
10-6 10-3 1
10-2
0.1
A thought experiment: Adding mass (slowly) to Earth …
Mass ( )
Radius
Earth
Jupiter
10-6 10-3 1
10-2
0.1
A thought experiment: Adding mass (slowly) to Earth …
Mass ( )
Radius
Earth
Jupiter
10-6 10-3 1
Brown Dwarfs
10-2
0.1
A thought experiment: Adding mass (slowly) to Earth …
Mass ( )
Radius
Earth
Jupiter
White Dwarfs
10-6 10-3 1
Brown Dwarfs
10-2
0.1
A thought experiment: Adding mass (slowly) to Earth …
Mass ( )
Radius
Earth
Jupiter
White Dwarfs
10-6 10-3 1
Brown Dwarfs
10-2
0.1
Chandrasekhar mass:
(1910-1995)
Adding mass to a white dwarf:What happens when its mass exceeds the Chandrasekhar limit?
2000 kmWhite Dwarf 10-20 km
Neutron Star
Adding mass to a Neutron Star …
Mass ( )
Radius(km)
1 2
10
20
Adding mass to a Neutron Star …
Mass ( )
Radius(km)
1 2
10
20
Lattimer & Parkash 06
Why is there a maximum mass for neutron stars?
Force balance in a star:(Newtonian) Pressure balances Gravity <-- M
Why is there a maximum mass for neutron stars?
Tolman-Oppenheimer-Volkoff Equation:
Force balance in a star:(Einsteinian) Pressure balances Gravity <-- M, Pressure
===> Tolman-Oppenheimer-Volkoff Limit
Keep adding mass to a neutron star:What happens when its mass exceeds the maximum mass?
10-20 kmNeutron Star Black Hole
First demonstrated byOppenheimer & Snyder (1939)
“Dark Star” Concept: John Michell (1783) Pierre Laplace (1795)
M, REscape velocity:
• Bold suggestion: Combine Newtonian mechanics/Gravity with the particle description of light • Although “correct” answer, derivation wrong
“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
• Karl Schwarzschild (1916): The first exact solution to Einstein field equation
The horizon radius (Schwarzschild radius):
Ensiten field equation:
• Roy Kerr (1963): Solution for spinning black holes
Formation of Compact Objects in Astrophysics
White dwarfs evolve from stars with M < 8 Sun … ~
NGC 2392, the Eskimo Nebula (HST)
Neutron stars evolve from stars with M > 8 Sun … ~
Burrows 2000
Crab nebula
Black Holes evolve from stars with M > 30 (?) Sun … ~
W. Zhang et al (2003)
H-T Janka
Failed bounce/explosion ==> Fall back of stellar material==> BH formation
Collapse of rotating star==> spinning BH + disk==> Relativistic jet (?)==> Gamma-ray bursts
Supermassive Black Holes (106-109 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/cm3 for M=108 Sun
• How do supermassive BHs form? --- Merger of smaller black holes in galaxy merger --- Collapse of supermassive stars followed by gas accretion
M87
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
Isolated Neutron Starshave diverse observational manifestations
Isolated Neutron Stars
Radio pulsars
Isolated Neutron Stars
Radio pulsars
Harding & DL 2006
Radiation in all wavelengths: radio, IR, optical, X-rays, Gamma rays
(1 Tesla = 104 G)
Pulse Profiles of 7 Pulsars
D. Thompson
Pulsar magnetosphere:Region surrounding the neutron star
containing relativistic electrons/positrons
Pulsar as a unipolar generator
Rotation + B field ==> EMF
In Pulsars:
Charge particles can be acclerated tohigh energy
Pair Cascade in Pulsar Magnetosphere
• Accelerated particles emit photons • Photons decay into e+e- pairs in strong B field
D.Page
GLAST (launched 6/11/2008)The Gamma-ray Large Area Space Telescope
• 20 MeV -- 300 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
FAST (~2014)The Five-hundred-meter Aperture Spherical Telescope
MagnetarsNeutron stars powered by superstrongmagnetic fields (B>1014G)
Bursts/flares
Giant flares in 3 magnetars 12/04 flare of SGR1806-20 has E>1046erg
(>Sun radiates in 105 years)
Magnetars do not show persistent radio emission Connection with high-B radio pulsars?
Radio emission triggered by X-ray outbursts XTE J1810-197 (Camilo et al. 2006, Kramer et al.2007) 1E 1547.0=5408 (Camilo et al. 2007)
Exotic QED Processes in Magnetar Fields
• Photon splitting:
• Vacuum birefringence: (photon propagation affected by B field)
e+
e- photon photon
B=1013 G, E=5 keV, θB=45o
“Plasma+Vacuum” ==> Vacuum resonance
x
y
zk
B
Thermally Emitting Isolated NSs
Burwitz et al. (2003)
“Perfect” X-ray blackbody: RX J1856.5-3754
Spectral lines detected: (e.g., van Kerkwijk & Kaplan 06; Haberl 06) RXJ1308+2127 (0.2-0.3 keV) RXJ1605+3249 (~0.45 keV) RXJ0720-3125 (~0.3 keV) RXJ0420-5022 (~0.3 keV)? RXJ0806-4123 (~0.5 keV)? RBS 1774 (~0.7 keV)?
!
Matter (atoms, molecules, condensed matter) in Strong Magnetic Fields:
Critical Field:
Strong field: Property of matter is very different from zero-field
.Strong B field significantly increases the binding energy of atoms
For
E.g. at 1012G
at 1014G
Atoms combine to form molecular chains: E.g. H2, H3, H4, …
Atoms and Molecules
Chain-chain interactions lead to formation of 3D condensed matter
.
.
..
Binding energy per cell
Zero-pressure density
Condensed Matter
Isolated Neutron Stars
Radio pulsars
Magnetars AXPs and SGRs
Thermally emitting Isolated NSs
Central Compact Objects in SNRs
Millisecond Magnetars (central engine of long/soft GRBs?)
Normal/millisecond pulsarsHigh-B pulsarsGamma-ray pulsarsRadio bursters, RRATs etc
Reasons for diverse NS Behaviors: Rotation and Magnetic Fields
Isolated Black Holes …
Isolated Black Holes are boring(unobservable)
Mass accretion onto Black Holes
Stellar-mass BHs in binaries Supermassive BHs in Galaxies
Mass accretion onto Black Holes
Stellar-mass BHs in binaries Supermassive BHs in Galaxies
Accreting gas has angular momentum ==> Accretion diskFriction in the disk ===> emission in X-rays
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)
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
Probing Black Holes Using Variability of X-ray Emission
Quasi-Periodic Oscillations (QPOs) in Black-Hole X-ray Binaries
Remillard & McClintock 2006
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-reflectionin Disks
Merging Binary Neutron Stars/Black Holes
Orbital Decay of Hulse-Taylor Pulsar Binary
Taylor & Weisberg 2005
Nobel Prize 1993
Shibata et al. 2006
Merging NSs (NS/BH or NS/NS) as Central Engine of(short/hard) Gamma Ray Bursts
Gravitational Waveform: The Last Three minutes
Gravitational Waves• Warpage of Spacetime• Generated by time-dependent quadrupoles• Detector response to passage of GWs:
Kip Thorne
Laser Gravitational Wave Interferometer
LIGOLaser Interferometer Gravitational Observatory
Kip Thorne
Probing Neutron Star Equation of State Using Gravitational Waves from Binary Merger
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
Thanks!
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
Probing BH using its AccretionDisk