Abstract
Two new observational windows have been opened to strong gravitational physics: gravitational waves, and very long baseline interferometry. This suggests observational searches for new phenomena in this regime, and in particular for those necessary to make black hole evolution consistent with quantum mechanics. We describe possible features of "compact quantum objects" that replace classical black holes in a consistent quantum theory, and approaches to observational tests for these using gravitational waves. This is an example of a more general problem of finding consistent descriptions of deviations from general relativity, which can be tested via gravitational wave detection. Simple models for compact modifications to classical black holes are described via an effective stress tensor, possibly with an effective equation of state. A general discussion is given of possible observational signatures, and of their dependence on properties of the colliding objects. The possibility that departures from classical behavior are restricted to the near-horizon regime raises the question of whether these will be obscured in gravitational wave signals, due to their mutual interaction in a binary coalescence being deep in the mutual gravitational well. Numerical simulation with such simple models will be useful to clarify the sensitivity of gravitational wave observation to such highly compact departures from classical black holes.
Highlights
With a steadily increasing number of gravitational wave observations from coalescing binaries [1], and with imminent new data from very long baseline interferometric (VLBI) observations of apparent black holes [2], we have entered a new era of observationally testing strong-field gravity
This is due to the requirement that for ultimate unitarity of black hole evolution, information needs to transfer out of a black hole while it is still of macroscopic size, in direct contradiction with a description based on classical geometry, together with small perturbations due to local quantum fields
While the models we study are limited in their ability to capture possible compact quantum objects (CQOs) properties, they should allow initial investigation of some of the basic questions regarding gravitational wave sensitivity to very compact departures from classical black hole (CBH)
Summary
With a steadily increasing number of gravitational wave observations from coalescing binaries [1], and with imminent new data from very long baseline interferometric (VLBI) observations of apparent black holes [2], we have entered a new era of observationally testing strong-field gravity. This suggests one general approach to investigating departures from CBHs that have consistent nonlinear evolution, namely to parametrize them in terms of an effective stress tensor, and in even simpler models, in terms of an effective equation of state (EOS) Such models, if they produce objects with relevant masses, begin to provide simple foils for coalescence of CBHs. After further discussion of motivation and CQO scenarios, Sec. III will describe such an effective approach and its use to formulate simple models to test aspects of possible modifications to CBH behavior, such as with CQOs. Section IV will investigate spherically symmetric solutions for such models, and in particular those with an EOS that permits them to be highly compact, in line with preceding comments. This paper will begin to investigate some models for certain kinds of deviation from classical black hole behavior, in an effective approach
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