Exact models of charged black holes

Inner geometry and embedding formulas for a totally geodesic null hypersurface in an electrovacuum space-time are given. The structure of all possible symmetry groups of the geometry is described in case that the space-like sections and are compact orientable surfaces and is, topologically, ×R ¹. The result is, where are the well-known isometry groups of , and is an at most two-dimensional group acting along rays, which is fully specified in the paper. It is not shown that all these symmetry types exist, but this will be done in the next papers where all horizons of a given symmetry type will be explicitly written down.Devoted to Professor André Mercier who is sixty in April, 1973.     

Near-horizon states of black holes and Calogero models

We find self-adjoint extensions of the rational Calogero model in the presence of the harmonic interaction. The corresponding eigenfunctions may describe the near-horizon quantum states of certain types of black holes.     

Connecting black holes and black strings

Static vacuum spacetimes with one compact dimension include black holes with localized horizons but also uniform and nonuniform black strings where the horizon wraps over the compact dimension. We present new numerical solutions for these localized black holes in 5 and 6 dimensions. Combined with previous 6D nonuniform string results, these provide evidence that the black hole and nonuniform string branches join at a topology changing solution.     

D0-branes in Gepner models and N = 2 black holes

In this paper D-brane boundary states constructed in Gepner models are used to analyze some aspects of the dynamics of DO-branes in Calabi-Yau compactifications of type II theories to four dimensions. It is shown that the boundary states correspond to BPS objects carrying dyonic charges. By analyzing the couplings to closed string fields a correspondence between the DO-branes and extremal charged black holes in N = 2 supergravity is found.     

Fragile black holes

The AdS/CFT correspondence may give a new way of understanding field theories in extreme conditions, as in the quark–gluon plasma phase of quark matter. The correspondence normally involves asymptotically AdS black holes with dual field theories which are defined on locally flat boundary spacetimes; the implicit assumption is that the distortions of spacetime which occur under extreme conditions do not affect the field theory in any unexpected way. However, AdS black holes are [to varying degrees] fragile, in the sense that they become unstable to stringy effects when their event horizons are sufficiently distorted. This implies that field theories on curved backgrounds may likewise be unstable in a suitable sense. We investigate this phenomenon, focussing on the “fragility” of AdS₅ black holes with flat event horizons. We find that, when they are distorted, these black holes are always unstable in string theory. This may have consequences for the detailed structure of the quark matter phase diagram at extreme values of the spacetime curvature.     

Almost certain escape from black holes in final state projection models

Recent models of the black-hole final state suggest that quantum information can escape from a black hole by a process akin to teleportation. These models rely on a controversial process called final-state projection. This Letter discusses the self-consistency of the final-state projection hypothesis and investigates escape from black holes for arbitrary final states and for generic interactions between matter and Hawking radiation. Quantum information escapes with fidelity approximately = (8/3pi)2: only half a bit of quantum information is lost on average, independent of the number of bits that escape from the hole.     

Stellar dynamics and black holes

Chandrasekhar’s most important contribution to stellar dynamics was the concept of dynamical friction. I briefly review that work, then discuss some implications of Chandrasekhar’s theory of gravitational encounters for motion in galactic nuclei.     

Axionic black holes and wormholes

Theories in which gravity is coupled to a Kalb-Ramond field are known to have black hole solutions characterized by the value of the conserved axion charge. The Kalb-Ramond field configuration for these black holes has vanishing field strength. The axion charge may be measured by an analog of the Aharanov-Bohm interference effect. The axion-charge to mass ratio may be arbitrarily large, as contrasted to the case of the Reissner-Nordstrom black hole where the electric-charge to mass ratio has an upper bound of one. The generic endpoint of semiclassical evaporation of an axionic black hole would therefore be an object of very large axion charge with mass of order the Planck mass. Axion charge also couples to Giddings-Strominger type instantons (wormholes) present in these theories. Instead of evaporating completely, therefore, it is likely that an axionic black hole will be swallowed by a wormhole, avoiding the appearance of a naked singularity. The loss of quantum coherence is a more subtle issue.This essay received the third award from the Gravity Research Foundation for the year 1989-Ed.On leave from the Physics Department, Syracuse University, Syracuse NY 13244-1130, USA.     

D-branes and fat black holes

The application of D-brane methods to large black holes whose Schwarzschild radius is larger than the compactification scale is problematic. Callan and Maldacena have suggested that despite apparent problems of strong interactions when the number of branes becomes large, the open string degrees of freedom may remain very dilute due to the growth of the horizon area which they claim grows more rapidly than the average number of open strings. Such a picture of a dilute weakly coupled string system conflicts with the picture of a dense string soup that saturates the bound of one string per Planck area. A more careful analysis shows that Callan and Maldacena were not fully consistent in their estimates. In the form that their model was studied it can not be used to extrapolate to large mass without being in conflict with the Hawking-Bekenstein entropy formula. A somewhat modified model can reproduce the correct entropy formula. In this “improved model” the number of string bits on the horizon scales like the entropy in agreement with earlier speculations of Susskind.     

Stefan-Boltzmann law for black bodies and black holes

Since black holes radiate with a thermal spectrum and therefore possess a radiation pressure, Boltzmann's derivation of Stefan's Law can be applied to black holes. In order that the entropy be proportional to the surface area of the black hole, the pressure must be negative. If the second law is not to be violated, then the temperature must also be negative. This leads to a canonical formulation for fluctuations. A comparison with other approaches is given and doubts are raised concerning the validity of conventional black hole thermodynamics.