1. Gravity with the SKA Michael Kramer Jodrell Bank Observatory University of Manchester With Don Backer, Jim Cordes, Simon Johnston, Joe Lazio and Ben Stappers Gravity Meeting ’06, Birmingham Michael Kramer Jodrell Bank Observatory University of Manchester With Don Backer, Jim Cordes, Simon Johnston, Joe Lazio and Ben Stappers Gravity Meeting ’06, Birmingham Strong-field tests of gravity using Pulsars and Black Holes Strong-field tests of gravity using Pulsars and Black Holes

2. Outline 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

3. A frequently asked question, still…

4. Testing 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: Solar system:

5. Pulsars are extreme objects… Cosmic lighthouses … Precise clocks … Almost Black Holes … Objects of extreme matter … –10x nuclear density –B ~ B q = 4.4 x 10 13 Gauss –Voltage drops ~ 10 12 V –F EM = 10 10-12 F g –High-temperature & superfluid superconductor Massive stable flywheels  superb cosmic clocks e.g. period of B1937+21 : P = 0.0015578064924327  0.0000000000000004 s Precision tools for a wide range of fundamental physics and astrophysics

6. The importance of pulsar tests log(Self-energy) log(Orbital energy)

7. Strong-field tests using 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

8. 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 11 Preferred-frame effects? Orbital polarization 0  1 < 10 -4  1 < 1.2 10 -4 Lunar ranging (weak) Pulsars (strong) 22 Preferred-frame effects? Spin precession 0  2 < 4 10 -7 Solar alignment 33 Preferred-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

9. …already a success story: The first binary pulsar Weisberg & Taylor (2004) Orbit shrinks every day by 1cm Confirmation of existence of gravitational waves Hulse & Taylor (1974)

10. Tests 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 e.g. in GR:

11. Tests 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 m A and m B should exist Single unique point in a m A - m B diagram!

12. Tests 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 m A and m B should exist Single unique point in a m A - m B diagram! PK 1 PK 2 PK 3 Pass!

13. Tests 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 m A and m B should exist Single unique point in a m A - m B diagram! PK 3 PK 2 PK 1 Fail! N pk – 2 tests possible

14. …already a success story: The first double pulsar Kramer et al. (in prep.) Orbital Phase (deg) Delay (µs) s = sin(i)=0.9997±0.0002 Kramer et al.(in prep) Testing GR: most relativistic systems most over-constrained system: Five PK params Theory independent mass ratio

15. Double Pulsar: Tests of GR December 2003 (Lyne et al. 2004)

16. Double Pulsar: Tests of GR Kramer et al. in prep.

17. “Scalarisation” …already a success story: Scalar-Tensor Theories Scalar Charge (for  0 =-6) Damour (priv. comm.)

18. 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)

19. Galactic 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!

20. Galactic probes: Interstellar medium/magnetic field Star formation history Dynamics Population via distances (ISM, VLBI) Pulsar Science with the SKA Very wide range of applications: Electron Electron distribution distribution Electron Electron distribution distribution Magnetic field Galactic Centre Movement in potential

21. Galactic probes Extragalactic pulsars: Formation & Population Turbulent magnetized IGM Pulsar Science with the SKA Very wide range of applications: Giant pulses Reach the local group! Search nearby galaxies!

22. Galactic probes Extragalactic pulsars Relativistic plasma physics: Radio emission Resolving magnetospheres Relation to high-energies Pulsar Science with the SKA Very wide range of applications:

23. 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 SKA Very wide range of applications:

24. Galactic probes Extragalactic pulsars Relativistic plasma physics Extreme Dense Matter Physics Multi-wavelength studies: Photonic windows Pulsar Science with the SKA Very wide range of applications:

25. Galactic probes Extragalactic pulsars Relativistic plasma physics Extreme Dense Matter Physics Multi-wavelength studies: Photonic windows Non-photonic windows Pulsar Science with the SKA Very wide range of applications:

26. 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 SKA Very wide range of applications: 3.Holy Grail: PSR-BH Double Pulsars Planets

27. 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 SKA Very wide range of applications:

28. Black Hole spin: Black Hole properties Astrophysical black holes are expected to rotate 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)

29. Black Hole quadrupole moment: Black Hole properties Spinning black holes are oblate Q = quadrupole moment Result is classical spin-orbit coupling Visible as transient signals in timing residuals Even more difficult! Requires SKA! Wex & Kopeikin (1999):

30. Cosmic Censorship Conjecture In GR at centre of BH, space-time diverges in point of infinite density: a singularity! Physical behaviour of singularities unknown What happens to space-time when it “sees” singularity? Penrose (1969): “Cosmic Censorship Conjecture” All singularities are hidden within Event Horizon of BH! They cannot seen by outside world, i.e. No “Naked Singularities” allowed! or: Complete grav.collapse always results in a BH!

31. For all compact massive, BH-like objects, we’ll be able to measure spin very precisely In GR, for Kerr-BH we expect: But if we measure  > 1  Event Horizon vanishes  Naked singularity! Then: either GR is wrong or Censorship Conjecture is violated! Cosmic Censorship Conjecture

32. No-hair theorem Like in Newtonian physics, one expects a relationship between  and q In GR, this relationship is very simple For Kerr-BH we expect: It reflects “no-hair” theorem: The BH has lost all information about Collapsed progenitor star, but an astrophysical (uncharged) BH is fully described by its mass and spin!

33. No-hair theorem If we measure either GR is wrong, i.e. “no-hair” theorem is violated or we have discovered a new kind of object, e.g. a Boson star with

34. Was Einstein right? What are the Black Hole properties? Do naked singularities exist? Do Black Holes have “hairs”? Fundamental Physics with the 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)

35. The SKA sky!