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The ability to model the evolution of compact binaries from the inspiral to coalescence is central to gravitational wave astronomy. Current waveform catalogues are built from vacuum binary black hole models, by evolving Einstein equations numerically and complementing them with knowledge from slow-motion expansions. Much less is known about the coalescence process in the presence of matter, or in theories other than general relativity. Here, we explore the close limit approximation as a powerful tool to understand the coalescence process in general setups. In particular, we study the head-on collision of two equal-mass, compact but horizonless objects. Our results show the appearance of ‘echoes’ and indicate that a significant fraction of the merger energy goes into these late-time repetitions. We also apply the close limit approximation to investigate the effect of colliding black holes on surrounding scalar fields. Notably, our results indicate that observables obtained through perturbation theory may be extended to a significant segment of the merger phase, where in principle only a numerical approach is appropriate. [ABSTRACT FROM AUTHOR]

In linear perturbation theory, a static perturber in the vicinity of a Schwarzschild black hole (BH) enhances [suppresses] the Gauss-Bonnet (GB) curvature invariant, R GB , in the high [low] tide regions. By analysing exact solutions of the vacuum Einstein field equations describing one or two BHs immersed in a multipolar gravitational field, which is locally free of pathologies, including conical singularities, we study the corresponding non-linear tides on a fiducial BH, in full General Relativity (GR). We show that the tidal field due to a far away, or close by, static BH creates high/low tides that can deviate not only quantitatively but also qualitatively from the weak field/Newtonian pattern. Remarkably, the suppression in low tide regions never makes R GB negative on the BH, even though the horizon Gaussian curvature may become negative; but R GB can vanish in a measure zero set, a feature qualitatively recovered in a Newtonian analogue model. Thus, purely gravitational, static, tidal interactions in GR, no matter how strong, cannot induce GB− scalarization. We also show that a close by BH produces noticeable asymmetric tides on another (fiducial) BH. [ABSTRACT FROM AUTHOR]

In the presence of certain non-minimal couplings between a scalar field and the Gauss-Bonnet curvature invariant, Kerr black holes can scalarize, as long as they are spinning fast enough. This provides a distinctive violation of the Kerr hypothesis, occurring only for some high spin range. In this paper we assess if strong magnetic fields, that may exist in the vicinity of astrophysical black holes, could facilitate this distinctive effect, by bringing down the spin threshold for scalarization. This inquiry is motivated by the fact that self-gravitating magnetic fields, by themselves, can also promote "spin-induced" scalarization. Nonetheless, we show that in the vicinity of the horizon the effect of the magnetic field B on a BH of mass M , up to B M ≲ 1 , works against spin-induced scalarization, requiring a larger dimensionless spin j from the black hole. A geometric interpretation for this result is suggested, in terms of the effects of rotation vs. magnetic fields on the horizon geometry. • New conceptual design methodology that integrates reliability for multirotors. • Controllability analysis based on ACAI adapted for failures and reliability analysis. • Sizing based on analytical database-free methodology with MDO. • Introducing failure case sizing factors to link controllability analysis with sizing. • Major impact of reliability considerations on UAV design and rotor specifically. [ABSTRACT FROM AUTHOR]

Bosonic fields can give rise to self-gravitating structures. These are interesting hypothetical new "dark matter stars" and good descriptions of dark matter haloes if the fields are very light. We study the dynamical response of Newtonian boson stars (NBS) when excited by external matter (stars, planets or black holes) in their vicinities. Our setup can describe the interaction between a massive black hole and the surrounding environment, shortly after the massive body has undergone a "kick", due to the collapse of baryonic matter at the galactic center, or dark matter depletion as a reaction to an inspiralling binary. We perform the first self-consistent calculation of dynamical friction acting on moving bodies in these backgrounds. Binaries close to coalescence "stir" the NBS core, and backreaction affects gravitational waveforms at leading − 6 P N order with respect to the dominant quadrupolar term; the coefficient is too small to allow detection by next-generation interferometers. We also show that the gravitational collapse to a supermassive black hole at the center of a NBS is accompanied by only a small change in the surrounding core. The NBS eventually gets accreted, but for astrophysical parameters this occurs only after several Hubble times. [ABSTRACT FROM AUTHOR]