Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article A Metric for Gravitational Collapse Around a Schwarzschild Black Hole(World Scientific Publishing, 2023) Erdem, Recai; Demirkaya, Betül; Gültekin, KemalWe consider the problem of gravitational collapse of a fluid under the effect of a small Schwarzschild black hole (e.g. a primordial one). We assume the fluid initially may be approximated by a uniform homogeneous dust. Starting from this configuration we obtain a class of metrics under some physically justified assumptions. We find that the metric we obtain includes the dust collapse as a subcase. After discussing some basic properties of the solution, we discuss the case of dust collapse in more detail. We find that the radial and tangential pressures outside the horizon may take positive or negative values depending on the values of the parameters.Correction Correction To: “curved Space and Particle Physics Effects on the Formation of Bose–einstein Condensation Around a Reissner–nordstrøm Black Hole”(Springer, 2022) Erdem, Recai; Demirkaya, Betül; Gültekin, KemalAfter this correction Fig. 1 in [1] is replaced by Fig. 1 above which is essentially the same as the one in [1]. Figure 2 in [1] now becomes irrelevant. Figure 3 in [1] is replaced by Fig. 2 above which is essentially the same as the one in [1].Article Echoes From the Event Horizon of a Superfluid Vortex(IOP Publishing, 2022) Güven, Kaan; Demirkaya, BetülA vortex formed in the superfluid state of a Bose-Einstein condensate may exhibit superradiance a la blackhole for radially propagating acoustic fluctuations. The analogy is usually based on the so-called draining bathtub model of the vortex, in which an event horizon and ergosphere emerges when the radial velocity of the superfluid exceeds the propagation speed of sound in the condensate. The acoustic fluctuations mimic a massless scalar field in the curved Lorentzian space-time of the vortex and are governed by the Klein-Gordon wave equation. One common main approximation is the constant background density of the superfluid even in the presence of the vortex. This sets a constant relativistic sound speed. However, the vortex state solution of the Gross-Pitaevskii equation clearly shows that both the density and the speed of sound vary radially near the vortex core, where the event horizon and thus the superradiance will take place. What changes would this complex interdependence bring to the formulation and to the outcomes of the superradiance based on constant density approximation? Here, we recount this question posed under the guidance of Prof. Tekin Dereli and present recent results. We show that the self-consistent density modifies the amplification dynamics near the event horizon significantly, thereby altering the temporal and spectral fingerprint of the superradiance of the vortex.Article Citation - WoS: 2Citation - Scopus: 2Curved Space and Particle Physics Effects on the Formation of Bose-Einstein Condensation Around a Reissner-Nordstrom Black Hole(Springer, 2021) Erdem, Recai; Demirkaya, Betül; Gültekin, KemalWe consider two scalar fields interacting through a chi*chi phi*phi term in the presence of a Reissner-Nordstrom black hole. Initially, only chi particles are present. We find that the produced phi particles are localized in a region around the black hole and have a tendency toward condensation provided that phi particles are much heavier than the chi particles. We also find that such a configuration is phenomenologically viable only if the scalars and the black hole have dark electric charges.