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