and STRONG-FIELD GRAVITY University of Arizona DIMITRIOS PSALTIS BLACK HOLES

about STRONG-FIELD GRAVITY? University of Arizona DIMITRIOS PSALTIS can BLACK HOLES tell us anything

What measures the strength of the gravitational field? e.g., in the Schwarzschild spacetime potential the spacetime is far from flat when Gravity is strong (far from Newtonian) when

What measures the strength of the gravitational field? In the opposite extreme, what if we add, e.g., a cosmological constant? curvature Gravity is “ weak ” when

 The Equivalence Principle Newton’s Second Law  Einstein’s Equation Poisson’s Equation Relativistic Gravity Newtonian Gravity Newton’s Law of Gravity  The Spacetime Metric

Where does Einstein ’ s equation come from?

 Einstein ’ s equation derived from the Hilbert action: Ricci curvature Cosmological constant Gravity is “ weak ” when

How can we extend Einstein ’ s equation? higher-order (e.g., R 2 ) Gravity: Gravity is “ strong ” when

Redshift: TESTS OF GENERAL RELATIVITY Psaltis 2006 Eclipse Hulse-Taylor Mercury Moon Neutron Stars Galactic Black Holes AGN LIGO LISA GP-B Potential (GM/rc 2 )

Redshift: TESTS OF GENERAL RELATIVITY Psaltis 2006 Eclipse Hulse-Taylor Mercury Moon Neutron Stars Galactic Black Holes AGN GP-B EW Baryogenesis Nucleosynthesis

Thorne & Dykla 1971; Hawking 1974; Bekenstein 1974; Sheel et al Scalar-Tensor black holes are identical to GR ones! all R 2 terms any function of R … in the Palatini formalism Let ’ s add: a dynamical vector field Psaltis, Perrodin, Dienes, & Mocioiu 2007, PRL, submitted Always get Kerr Black Holes!!!

We can rely on phenomenological spacetimes e.g., measure coefficients of multipole expansions of the metric Ryan 1995; Collins & Hughes 2004 or even measure directly the metric elements from observations Psaltis 2007

Black holes can be used as null-hypothesis tests against alternative gravity theories that predict massive compact stars STABLE UNSTABLE DeDeo & Psaltis 2003 e.g., in scalar-tensor gravity, neutron stars can be heavy! ==

The Good News We have a parameter-free solution to an astrophysical problem! If experiments do not confirm it:  Strong Violation of Equivalence Principle!  Massive Gravitons!!!  Non-local physics!!!! Berti, Buonanno, Will 2005 e.g., Simon 1990, Adams et al  Large extra dimensions!! Emparan et al. 2002

log Tabletop experiments: IN A UNIVERSE WITH LARGE EXTRA DIMENSIONS, BLACK HOLES EVAPORATE VERY FAST DUE TO “ HAWKING ” RADIATION EMPARAN et al Large Extra Dimensions?

When did this happen? Mirabel et al XTE J

Table Top Limits Astrophysical Limit: L<0.08mm Constraining AdS Curvature of Extra Dimensions Psaltis 2007, PRL, in press

CONCLUSIONS (I) Gravity in the Strong-Field Regime has not been tested (II) Gravitational Fields of Neutron Stars and Stellar-Mass Black-Holes are the Strongest Found in the Universe  a great laboratory to perform gravitational tests (III) To Learn about Strong-Field Gravity with Black Holes we have to:  Resolve the relevant (msec) dynamical timescales  Develop a theoretical framework to quantify our results