# Gravitational Physics

Gravitational physics research involves studies of applications of numerical relativity, black hole dynamics, sources of gravitational radiation, critical phenomena in gravitational collapse, the initial value problem of general relativity, and relativistic astrophysics. Department faculty also undertake research on the cosmological constant, the holographic principle, the origin of the ultra-high energy cosmic rays, spacetime foam, and possible relations to LIGO/LISA physics.

#### Numerical relativity

Numerical relativity is used to obtain dynamical solutions of the nonlinear Einstein equations. The two primary purposes of these techniques are to probe the fundamental structure of the theory in circumstances where analytic solution is impossible (for example to study critical phenomena in gravitational collapse) and to model realistic sources of gravitational radiation (for example the merger of binary black holes).

#### Gravitational wave phenomenology

A new generation of sensitive, wideband gravitational wave detectors, based upon the use of laser interferometry, are beginning operation or in the process of construction. These facilities include the US LIGO project (Laser Interferometer Gravitational-wave Observatory) which has begun scientific operation. Theorists contribute to gravitational wave physics both by constructing numerical models of gravitational wave sources and by helping develop signal processing algorithms.

#### Relativistic astrophysics

Relativistic astrophysics includes the study of compact interacting binaries, neutron stars and pulsars, gamma-ray bursts, and black hole candidates.

#### Current and recent activities

Current activities of the UNC gravitational physics group include using a formulation of the initial value problem of general relativity to fashion sequences of quasi-equilibrium black hole binaries, studying outgoing wave solutions in the presence of spacetime curvature and developing radiative boundary conditions, and developing numerical methods for modeling hyperbolic systems. Other recent activities have included studies of critical phenomena in gravitational collapse and construction of hyperbolic formulations of the field equations of general relativity.