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Register a new userA wormhole geometry from gravitational collapse
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Soumya Chakrabarti
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We discuss a proposal on how gravitational collapse of a NEC (Null Energy Condition) violating spherically symmetric fluid distribution can avoid the formation of a zero proper volume singularity and eventually lead to a Lorentzian wormhole geometry. Our idea is illustrated using a time-evolving wormhole spacetime in which, we show how a collapsing sphere may never reach a zero proper volume end-state. The nature of geodesic congruences in such spacetimes is considered and analyzed. Our construction is inspired from a recently proposed static wormhole geometry, the multi-parameter Simpson-Visser line element, which is known to unite wormholes and black holes (regular and singular) in a single framework.
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Current ground-based gravitational wave detectors are tuned to capture the collision of compact objects such as stellar origin black holes and neutron stars; over 20 such events have been published to date. Theoretically, however, more exotic compact objects may exist, collisions of which should also generate copious gravitational waves. In this paper, we model the inspiral of a stellar mass black hole into a stable, non-spinning, traversable wormhole, and find a characteristic waveform -- an anti-chirp and/or burst -- as the black hole emerges, i.e., outspirals, into our region of the Universe. This novel waveform signature may be useful in searches for wormholes in future gravitational wave data or used to constrain possible wormhole geometries in our Universe.
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Black holes (BHs) play a central role in physics. However, gathering observational evidence for their existence is a notoriously difficult task. Current strategies to quantify the evidence for BHs all boil down to looking for signs of highly compact, horizonless bodies. Here, we study particle creation by objects which collapse to form ultra-compact configurations, with surface at an areal radius $R=R_{f}$ satisfying $1-(2M/R_{f})= epsilon^{2}ll 1$ with $M$ the object mass. We assume that gravitational collapse proceeds in a `standard manner until $R=R_{f}+2M epsilon^{2beta}$, where $beta>0$, and then slows down to form a static object of radius $R_{f}$. In the standard collapsing phase, Hawking-like thermal radiation is emitted, which is as strong as the Hawking radiation of a BH with the same mass but lasts only for $sim 40~(M/M_{odot})[44+ln (10^{-19}/epsilon)]~mu mbox{s}$. Thereafter, in a very large class of models, there exist two bursts of radiation separated by a very long dormant stage. The first burst occurs at the end of the transient Hawking radiation, and is followed by a quiescent stage which lasts for $sim 6times 10^{6}~(epsilon/10^{-19})^{-1}(M/M_{odot})~mbox{yr}$. Afterwards, the second burst is triggered, after which there is no more particle production and the star is forever dark. In a model with $beta=1$, both the first and second bursts outpower the transient Hawking radiation by a factor $sim 10^{38}(epsilon/10^{-19})^{-2}$.
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