Gravity with the SKAGravity with the SKAGravity with the SKAGravity with the SKA

Michael KramerJodrell Bank ObservatoryUniversity of Manchester

WithDon Backer, Jim Cordes, Simon Johnston,

Joe Lazio and Ben Stappers

Gravity Meeting ’06, Birmingham

Michael KramerJodrell Bank ObservatoryUniversity of Manchester

WithDon Backer, Jim Cordes, Simon Johnston,

Joe Lazio and Ben Stappers

Gravity Meeting ’06, Birmingham

Strong-field tests of gravity using Pulsars and Black HolesStrong-field tests of gravity

using Pulsars and Black Holes

OutlineOutline• Pulsars• Past and present successes • A giant leap - the power of the SKA• Transforming our knowledge of fundamental physics, particularly:

- Strong-field tests of gravity - Gravitational wave astronomy Searching & Timing: see Jim Gravitational Waves: see Rick

A frequently asked question, A frequently asked question, still…still…

Testing EinsteinTesting Einstein

Experiments made in Solar System provide accurate tests …but only in weak gravitational field!

In strong gravitational fields, physics may be different!

Compute energy in gravitational field:

Radiative aspects need to be tested too!

Neutron stars &Black Holes:

5.0

15.0

BH

NS

2mc

EgravitySolar system:

10000000000.0

0000000001.0

000001.0

Moon

Earth

Sun

Pulsars are extreme objects…Pulsars are extreme objects…• Cosmic lighthouses …• Precise clocks …• Almost Black Holes …• Objects of extreme matter …

– 10x nuclear density– B ~ Bq = 4.4 x 1013 Gauss– Voltage drops ~ 1012 V– FEM = 1010-12 Fg – High-temperature & superfluid superconductor

• Massive stable flywheels superb cosmic clocks e.g. period of B1937+21: P = 0.00155780649243270.0000000000000004 s

Precision tools for a wide range of fundamental physics and astrophysics

The importance of pulsar The importance of pulsar teststests

log

(Self

-en

erg

y)

log(Orbital energy)

Strong-field tests using Strong-field tests using pulsars…pulsars…

Various approaches:

Theory-independent or phenomenological:Parameterized Post-Keplerian approach

Parameterized Post-Newtonian (PPN)

Binary pulsars

Theory-dependent: Beyond usual post-Newtonian parameters, used for classes of tensor-scalar theories

Parametrized post-Newtonian (PPN)Parametrized post-Newtonian (PPN) How much space

curvature per unit mass?1 -1<2 10-3

-1<3 10-4

Viking ranging (time delay)

VLBI (light deflect.)

How much “non-linearity” in the superposition law?

1 -1<3 10-3 Perihelion shift

Preferred-location effects? 0 | |<3 10-3 Earth tides, Pulsars

1Preferred-frame effects?

Orbital polarization0 1 < 10-4

1 < 1.2 10-4

Lunar ranging (weak)

Pulsars (strong)

2Preferred-frame effects?

Spin precession0 2 < 4 10-7 Solar alignment

3Preferred-frame effects?

Violation of conversation of total momentum

0 3 < 4.0 10-20 Pulsars

Will (2002), Stairs (2005)

Plus: limits on violation of SEP: |Δ|<5.5x10-3

……already a success story:already a success story:The first binary pulsarThe first binary pulsar

Weisberg & Taylor (2004)

• Orbit shrinks every day by 1cm• Confirmation of existence of gravitational waves

Hulse & Taylor (1974)

Tests of General RelativityTests of General Relativity

Elegant method to test any theory of gravity: (Damour & Taylor ’92)

• Relativistic corrections to Keplerian orbits measured• All corrections can be written as function of the pulsar masses• Only one true combination of mA and mB should exist

Single unique point in

a mA - mB diagram!

PK1

PK2PK3

Pass!

Tests of General RelativityTests of General Relativity

Elegant method to test any theory of gravity: (Damour & Taylor ’92)

• Relativistic corrections to Keplerian orbits measured• All corrections can be written as function of the pulsar masses• Only one true combination of mA and mB should exist

Single unique point in

a mA - mB diagram!

PK3

PK2

PK1

Fail!

Npk – 2 tests possible

……already a success story: already a success story: The first double pulsarThe first double pulsar

Kramer et al. (in prep.)

Orbital Phase (deg)

Dela

y (

µs)

s = sin(i)=0.9997±0.0002

001.0000.1obs

exp

s

s

Kramer et al.(in prep)

Testing GR:

• most relativistic systems• most over-constrained system:

• Five PK params• Theory independent mass ratio

Double Pulsar: Tests of GRDouble Pulsar: Tests of GRDecember 2003 (Lyne et al. 2004)

Double Pulsar: Tests of GRDouble Pulsar: Tests of GRKramer et al. in prep.

“Scalarisation”

……already a success story: already a success story: Scalar-Tensor TheoriesScalar-Tensor Theories

Scalar

Charge

(for 0=-6)

Damour (priv. comm.)

Damour (priv. comm.)

The is more to do:The is more to do:

• The remaining “holy grail”: a pulsar – black hole system!• Wanted: millisecond pulsar around black hole

“…a binary pulsar with a black-hole companion has the potential of providing a superb new probe of relativistic gravity. The discriminating power of this probe might supersede all its present and foreseeable competitors…”

(Damour & Esposito-Farese 1998)

Galactic Census with the SKAGalactic Census with the SKA

• Blind survey for pulsars will discover PSR-BH systems!• Timing of discovered binary and millisecond pulsars to very high precision:

• “Find them!”• “Time them!”• “VLBI them!”

Benefiting from SKA twice:• Unique sensitivity: many pulsars, ~10,000-20,000 incl. many rare & exotic systems!• Unique timing precision and multiple beams!Not just a continuation of what has been done before - Complete new quality of science possible!

• Galactic probes: Interstellar medium/magnetic field Star formation history Dynamics Population via distances (ISM, VLBI)

Pulsar Science with the SKAPulsar Science with the SKA Very wide range of applications:

ElectronElectron

distributiondistribution

ElectronElectron

distributiondistribution

Magnetic fieldMagnetic field

Galactic CentreMovement in potential

• Galactic probes• Extragalactic pulsars: Formation & Population Turbulent magnetized IGM

Pulsar Science with the SKAPulsar Science with the SKA Very wide range of applications:

Giant pulsesGiant pulses

Reach the local group!

Search nearby galaxies!

• Galactic probes• Extragalactic pulsars• Relativistic plasma physics: Radio emission Resolving magnetospheres Relation to high-energies

Pulsar Science with the SKAPulsar Science with the SKA Very wide range of applications:

• Galactic probes• Extragalactic pulsars• Relativistic plasma physics• Extreme Dense Matter Physics: Ultra-strong B-fields Equations-of-State Core collapses Variation of G

Pulsar Science with the SKAPulsar Science with the SKA Very wide range of applications:

• Galactic probes• Extragalactic pulsars• Relativistic plasma physics• Extreme Dense Matter Physics• Multi-wavelength studies: Photonic windows

Pulsar Science with the SKAPulsar Science with the SKA Very wide range of applications:

• Galactic probes• Extragalactic pulsars• Relativistic plasma physics• Extreme Dense Matter Physics• Multi-wavelength studies: Photonic windows Non-photonic windows

Pulsar Science with the SKAPulsar Science with the SKA Very wide range of applications:

• Galactic probes• Extragalactic pulsars• Relativistic plasma physics• Extreme Dense Matter Physics• Multi-wavelength studies• Exotic systems: planets millisecond pulsars relativistic binaries double pulsars PSR-BH systems

Pulsar Science with the SKAPulsar Science with the SKA Very wide range of applications:

3.Holy Grail: PSR-BH

Double PulsarsPlanets

• Galactic probes• Extragalactic pulsars• Relativistic plasma physics• Extreme Dense Matter Physics• Multi-wavelength studies• Exotic systems• Gravitational physics: - Strong-field tests - BH properties - Gravitational Waves

Pulsar Science with the SKAPulsar Science with the SKA Very wide range of applications:

Black Hole spin:

Black Hole properties Black Hole properties

•Astrophysical black holes are expected to rotate

2M

S

G

c S = angular

momentum

• Result is relativistic spin-orbit coupling• Visible as a precession of the orbit: Measure higher order derivatives of secular changes in semi-major axis and longitude of periastron• Not easy! It is not possible today!• Requires SKA sensitivity!

See Wex & Kopeikin (1999)xx ,,

Black Hole quadrupole moment:

Black Hole properties Black Hole properties

•Spinning black holes are oblate

Q = quadrupole moment

32

4

M

Q

G

cq

• Result is classical spin-orbit coupling• Visible as transient signals in timing residuals• Even more difficult! • Requires SKA!

We

x & K

op

eikin

(1

999

):

• For all compact massive, BH-like objects, we’ll be able to measure spin very precisely• In GR, for Kerr-BH we expect:

1• But if we measure > 1 Event Horizon vanishes Naked singularity!

• Then: either GR is wrong or Censorship Conjecture is violated!

Cosmic Censorship Cosmic Censorship Conjecture Conjecture

No-hair theorem No-hair theorem

2q

• If we measure

either GR is wrong, i.e. “no-hair” theorem is violatedor we have discovered a new kind of object, e.g. a Boson star with

210q

Was Einstein right? What are the Black Hole properties? Do naked singularities exist? Do Black Holes have “hairs”?

Fundamental Physics with the Fundamental Physics with the SKA SKA

Pulsars discovered and observed with the SKA…

• complement studies in other windows • probe wide range of physical problems• New science possible – not just the same:

Work to be done: 2PN timing formula Calibration techniques Means to handle blind survey Efficient timing methods (LOTS of data, LOTS of pulsars)

The SKA sky!The SKA sky!