arXiv subjects

E. M. Howard

Publications and source records attributed to E. M. Howard.

5 recordsLinked to original sources

arXiv2016

Modelling the flare activity of Sgr A*

Latest observational data provides evidence that the emissions from Sgr A* originate from an accretion disc within ten gravitational radii of the dynamical centre of Milky Way. We investigate the physical processes responsible for the variable observed emissions from the compact radio source Sgr A*. We study the evolution of the variable emission region and analyse light curves and time-resolved spectra of emissions originated at the surface of the accretion disk, close to the event horizon, near the marginally stable orbit of a Kerr black hole.

astro-ph.HE↗

arXiv2016

Modelling the flaring emission at the Galactic Centre

The massive black hole at the Galactic Centre is known to be variable in radio, millimeter, near-IR and X-rays. We investigate the physical processes responsible for the variable observed emissions from the compact radio source Sgr A*. We study the evolution of the variable emission region and present light curves and time-resolved spectra of emissions from the accretion disk, close to the event horizon, near the marginally stable orbit of a Kerr black hole.

astro-ph.HE↗

arXiv2016

Relativistic Signatures at the Galactic Center

Studies of the inner few parsecs at the Galactic Centre provide evidence of a supermassive black hole, associated with the unusual, variable radio and infrared source Sgr A*. Our major aim is the study and analysis of the physical processes responsible for the variable emission from the compact radio source Sgr A*. In order to understand the physics behind the observed variability, we model the time evolution of the flare emitting region by studying light curves and spectra of emission originating at the surface of the accretion disk, close to the event horizon, near the marginally stable orbit of a rotating black hole. Here we discuss the methods used in the analysis of the time-variable spectral features and subsequently present preliminary modeling results.

astro-ph.HE↗

arXiv2016

Causal structure of general relativistic spacetimes

We present some of the recent results and open questions on the causality problem in General Relativity. The concept of singularity is intimately connected with future trapped surface and inner event horizon formation. We offer a brief overview of the Hawking Penrose singularity theorems and discuss a few open problems concerning the future Cauchy development (domain of dependence), breakdown criteria and energy conditions for the horizon stability. A key question is whether causality violating regions, generating a Cauchy horizon are allowed. We raise several questions concerning the invisibility and stability of closed trapped surfaces from future null infinity and derive the imprisonment conditions. We provide an new perspective of the causal boundaries and spacelike conformal boundary extensions for time oriented Lorentzian manifolds and more exotic settings.

gr-qc↗

arXiv2016

Causal Stability Conditions for General Relativistic Spacetimes

A brief overview of some open questions in general relativity with important consequences for causality theory is presented, aiming to a better understanding of the causal structure of the spacetime. Special attention is accorded to the problem of fundamental causal stability conditions. Several questions are raised and some of the potential consequences of recent results regarding the causality problem in general relativity are presented. A key question is whether causality violating regions are locally allowed. The new concept of almost stable causality is introduced; meanwhile, related conditions and criteria for the stability and almost stability of the causal structure are discussed.

gr-qc↗