Tests of Strong-Field General Relativity

In contrast to gravity in the weak-field regime, which has been subjected to numerous experimental tests, gravity in the strong-field regime is largely unconstrained by experiments. A large class of gravity theories can be constructed that obey the Einstein equivalence principle and cannot be rejected by solar system tests, but that diverge from general relativity in the strong-field regime. Our aim is to design new tests of general relativity that are specific to its strong-field behavior.

Have a look at:

• Kerr Black Holes are Not Unique to General Relativity, Psaltis, Perrodin, Dienes, & Mocioiu (2007) Phys. Rev. Lett, in press
• Testing General Metric Theories of Gravity with Bursting Neutron Stars, Psaltis (2007), Phys. Rev. D., in press
• Constraints on Braneworld Gravity from a limit on the Kinematic Age of the Black Hole Source XTE J1118+480, Psaltis (2007), Phys. Rev. Let,
• Constraining Brans-Dicke Gravity with Millisecond Pulsars in Ultracompact Binaries, Psaltis (2007), ApJ, in press
• Testing Strong-field Gravity with Quasi-Periodic Oscillations, DeDeo & Psaltis (2006), PRD, submitted
• Towards New Tests of Strong-field Gravity with Measurements of Surface Atomic Line Redshifts from Neutron Stars, DeDeo & Psaltis (2003), PRL, 90, 141101
• Measurements of Black Hole Spins and Tests of Strong-Field General Relativity, Psaltis (2004), in X-Ray Timing 2003: Rossi and Beyond for an earlier review

Magnetohydrodynamic Turbulence in Shearing Flows

Have a look at:

• Spectral Methods for Time-Dependent Studies of Accretion Flows. III. Three-dimensional Magnetohydrodynamic Disks, Chan, Psaltis, & Özel (2007), ApJ, submitted
• The fundamental difference between alpha viscosity and turbulent magnetorotational stresses, Pessah, Chan, & Psaltis (2007), MNRAS in press
• Angular Momentum Transport in Accretion Disks: Scaling Laws in MRI-driven Turbulence, Pessah, Chan, & Psaltis (2007), ApJ 668, L51
• A Local Model of Angular Momentum Transport in Accretion Disks Driven by the Magnetorotational Instability, Pessah, Chan, & Psaltis (2006), PRL, 97, 221103
• The Signature of the Magnetorotational Instability in the Reynolds and Maxwell Stress Tensors in Accretion Disks, Pessah, Chan, & Psaltis (2006), MNRAS, 372, 183
• Spectral Methods for Time-Dependent Studies of Accretion Flows. II. Two-dimensional Hydrodynamic Disks with Self Gravity, Chan, Psaltis, & Özel (2006), ApJ, 645, 506
• The Stability of Magnetized Rotating Plasmas with Superthermal Fields, Pessah & Psaltis (2005), ApJ, 628, 879
• Spectral Methods for Time-Dependent Studies of Accretion Flows. I. Two-dimensional, Viscous, Hydrodynamic Disks, Chan, Psaltis, & Özel (2005), ApJ, 628, 353

Variability of Accretion Flows Around Compact Objects

Black holes and neutron stars that accrete matter from their environments are highly variable at timescales ranging from months to milliseconds (for object of stellar mass). The fastest of these timescales correspond to phenomena that occur only a few Schwarzschild radii above the compact objects and provide the strongest evidence so far for the existence of heavy neutron stars and of rapidly spinning black holes in the universe. Our aim is to develop a physical model that accounts for the characteristics of this variability.

Have a look at:

• Models of Quasi-Periodic Variability in Neutron Stars and Black Holes, Psaltis (2002) in Proc. of 33 COSPAR assembly, for a rather old review
• A Unified Description of the Timing Features of Accreting X-ray Binaries, Belloni, Psaltis, & van der Klis (2002), ApJ, 572, 392
• Correlations in Quasi-Periodic Oscillation and Noise Frequencies Among Neutron-Star and Black-Hole X-ray Binaries, Psaltis, Belloni, & van der Klis (1999), ApJ, 520 262