What does a binary black hole merger look like?

We present a method of calculating the strong-field gravitational lensing caused by many analytic and numerical spacetimes. We use this procedure to calculate the distortion caused by isolated black holes and by numerically evolved black hole binaries. We produce both demonstrative images illustrating details of the spatial distortion and realistic images of collections of stars taking both lensing amplification and redshift into account. On large scales the lensing from inspiraling binaries resembles that of single black holes, but on small scales the resulting images show complex and in some cases self-similar structure across different angular scales.Comment: 10 pages, 12 figures. Supplementary images and movies can be found at http://www.black-holes.org/the-science-numerical-relativity/numerical-relativity/gravitational-lensin

Simulated Radio and Neutrino Imaging of a Microquasar

Microquasar stellar systems emit electromagnetic radiation and high-energy particles. Thanks to their location within our own galaxy, they can be observed in high detail. Still, many of their inner workings remain elusive; hence, simulations, as the link between observations and theory, are highly useful. In this paper, both high-energy particle and synchrotron radio emissions from simulated microquasar jets are calculated using special relativistic imaging. A finite ray speed imaging algorithm is employed on hydrodynamic simulation data, producing synthetic images seen from a stationary observer. A hydrodynamical model is integrated in the above emission models. Synthetic spectra and maps are then produced that can be compared to observations from detector arrays. As an application, the model synthetically observes microquasars during an episodic ejection at two different spatio-temporal scales: one on the neutrino emission region scale and the other on the synchrotron radio emission scale. The results are compared to the sensitivity of existing detectors

A novel approach to relativistic ray-tracing technique in N-body simulations

N-body simulations are fundamental to cosmology and essential for high-precision investigations. Theoretical predictions are made in the simulations and compared to observations, owing to their known cosmological parameters, and hence makes them crucial for future tests of general relativity (GR) on cosmological scales – specifically, a test of GR via cosmic magnification in the weak lensing regime. Whilst N-body simulations are the theoretical tool that is requisite for generating mock weak lensing galaxy catalogues, it is ray-tracing technique that permits the study of light propagation within the catalogues; to trace simulated light paths through spacetime. However, there must be assurance that ray-tracing technique does not ignore the effects of gravitational lensing. Most studies simulate light paths along straight trajectories in three-dimensional space. Yet on larger scales, this assumption will lead to inaccuracies; photons follow a curved trajectory as they pass a gravitational field. A small number of relativistic ray-tracing codes have been developed to address this issue. Therefore, I investigate an existing relativistic ray-tracing algorithm and evaluate, experiment and modify the code for the purpose of testing GR physics via cosmic magnification in future research. A novel experimentation design has been applied to the code – a proof-of-concept methodological approach – that ultimately seeks to input an extended list of particle values and output gravitational lensing results. More specifically, the modified code assigns the non-gridded gravitational potentials from a Gadget-2 dark matter halo simulation file onto a three-dimensional grid, in which the values are interpolated and integrated through the remainder of the modified code. Gadget-2 simulation files are a popular choice for cosmologists and astrophysicists to conduct their studies of light propagation via ray-tracing, hence this modified design is a contribution to the field. Additionally, the results are further verified by establishing contour plots of the displacement angles, which will be compared to the projected mass surface density, Σ, in the next stage of research; by inputting the solutions to the geodesic equations and outputting a projection of the three-dimensional mass distribution onto a two-dimensional surface. This modified relativistic ray-tracing algorithm will be employed for an upcoming test of GR on cosmological scales, where the simulation will be populated with real data from the EMU radio galaxy survey. Theoretical predictions of cosmic magnification will be made, via the cross-correlation of distant radio galaxies and nearby optical galaxies, in which the lensing measurements will indicate if there is conformity to GR

Enseñanza de la estructura espacio-tiempo: un análisis bibliométrico (1988-2020) y futuras direcciones de investigación

Se efectuó un análisis bibliométrico de la producción científica con fines educativos, en todos los niveles, sobre la estructura del espacio-tiempo, para reconstruir la estructura intelectual, conceptual y de redes sociales de la comunidad científica implicada, en el periodo 1988 hasta agosto del 2020. La información se obtuvo de las bases de datos Web of Science, rastreando los valores lógicos “spacetime and teaching” o “spacetime and pedagogical”, totalizando ciento catorce artículos. Se siguió la metodología del análisis bibliométrico descriptivo. Los resultados y el análisis se muestran con Bibliometrix, una herramienta de código abierto para la investigación cuantitativa en cienciometría y bibliometría. Se concluyó que la estructura del espacio-tiempo está fuertemente presente en la relatividad general, teoría cuántica y en las soluciones de Schwarzschild y que los modelos pedagógicos están relacionados con los tópicos de la teoría de campos cuánticos, mientras que la enseñanza la física busca comprender la estructura del espacio tiempo en la teoría especial y general de la relatividad

Strong-field gravitational lensing by black holes

In this thesis we study aspects of strong-field gravitational lensing by black holes in general relativity, with a particular focus on the role of integrability and chaos in geodesic motion. We first investigate binary black hole shadows using the Majumdar–Papapetrou static binary black hole (or di-hole) solution. It is shown that the propagation of null geodesics on this spacetime background is a natural example of chaotic scattering. We demonstrate that the binary black hole shadows exhibit a self-similar fractal structure akin to the Cantor set. Next, we use techniques from the field of non-linear dynamics to quantify these fractal structures in binary black hole shadows. Using a recently developed numerical algorithm, called the merging method, we demonstrate that parts of the Majumdar–Papapetrou di-hole shadow may possess the Wada property. We then study the existence, stability and phenomenology of circular photon orbits in stationary axisymmetric four-dimensional spacetimes. We employ a Hamiltonian formalism to describe the null geodesics of the Weyl–Lewis–Papapetrou geometry. Using the Einstein–Maxwell equations, we demonstrate that generic stable photon orbits are forbidden in pure vacuum, but may arise in electrovacuum. Finally, we apply a higher-order geometric optics formalism to describe the propagation of electromagnetic waves on Kerr spacetime. Using the symmetries of Kerr spacetime, we construct a complex null tetrad which is parallel-propagated along null geodesics; we introduce a system of transport equations to calculate certain Newman–Penrose quantities along rays; we derive generalised power series solutions to these transport equations through sub-leading order in the neighbourhood of caustic points; and we introduce a practical method to evolve the transport equations beyond caustic points