Scholar iON
Academic Synthesis
The selected scholarly papers collectively explore diverse aspects of astrophysics, ranging from computational methods to theoretical and historical insights. Romeo et al. (2004) introduce a wavelet-based code for enhancing the precision of N-body simulations by efficiently de-noising data, reflecting advancements in computational astrophysics that leverage mathematical tools for future-oriented performance gains. Luminet (1998) and Dovciak et al. (2004) delve into black hole physics, with Luminet providing a foundational overview of black holes’ role in understanding cosmic phenomena, and Dovciak et al. presenting a sophisticated model for analyzing X-ray spectra from black-hole accretion discs, underscoring the complexity and dynamism of spectral analysis in strong gravity contexts. Shaviv (2011) addresses the historical discourse on the discovery of the expanding universe, specifically examining the controversy surrounding Hubble and Lemaitre, ultimately rejecting claims of plagiarism while highlighting the nuanced nature of scientific recognition and credit. This body of research underscores the interdisciplinary and evolving nature of astrophysical studies, bridging computational advancements, theoretical exploration, and historical analysis.
Wavelets are a new and powerful mathematical tool, whose most celebrated applications are data compression and de-noising. In Paper I (Romeo, Horellou & Bergh 2003, astro-ph/0302343), we have shown that wavelets can be used for removing noise efficiently from cosmological, galaxy and plasma N-body simulations. The expected two-orders-of-magnitude higher performance means, in terms of the well-known Moore's law, an advance of more than one decade in the future. In this paper, we describe a wavelet add-on code designed for such an application. Our code can be included in common grid-based N-body codes, is written in Fortran, is portable and available on request from the first author. The code can also be applied for removing noise from standard data, such as signals and images.
Our understanding of space and time is probed to its depths by black holes. These objects, which appear as a natural consequence of general relativity, provide a powerful analytical tool able to examine macroscopic and microscopic properties of the universe. This introductory article presents in a pictorial way the basic concepts of black hole's theory, as well as a description of the astronomical sites where black holes are suspected to lie, namely binary X-ray sources and galactic nuclei.
We report on a new general relativistic computational model enhancing, in various respects, the capability of presently available tools for fitting spectra of X-ray sources. The new model is intended for spectral analysis of black-hole accretion discs. Our approach is flexible enough to allow easy modifications of intrinsic emissivity profiles. Axial symmetry is not assumed, although it can be imposed in order to reduce computational cost of data fitting. The main current application of our code is within the XSPEC data-fitting package, however, its applicability goes beyond that: the code can be compiled in a stand-alone mode, capable of examining time-variable spectral features and doing polarimetry of sources in the strong-gravity regime. Basic features of our approach are described in a separate paper (Dovciak, Karas & Yaqoob 2004). Here we illustrate some of its applications in more detail. We concentrate ourselves on various aspects of line emission and Compton reflection, including the current implementation of the lamp-post model as an example of a more complicated form of intrinsic emissivity.
Recently Block published an astro-ph{http://arxiv.org/abs/1106.3928 (2011).} insinuating that Lemaitre discovery paper of the Expanding Universe was censored prior to its translation into English and publication in the Monthly Notices of the Royal Astronomical Society. Consequently, Lemaitre's credit for the discovery of the velocity-distance correlation was not recognized. We examine here the chain of events leading to the discovery of the 'Hubble law'. Our summary: (a) Lemaitre found a theoretical linear correlation between velocity and distance. (b) Lemaitre assumed the existence of a linear relation between velocity and distance and calculated the coefficient. (c) Hubble took the data plotted it and demonstrated that a linear relation represents the observed data. (d) Hubble never believed in Lemaitre's solution, namely in an expanding universe. Consequently, Hubble never cited Lemaitre. We conclude that the charge that Lemaitre's paper was censored or ignored let alone plagiarized by Hubble, is not founded, and explain why Lemaitre's earlier theoretical discovery and derived 'Hubble constant' was not cited or recognized, by Hubble as well as by many other leading researchers.