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Bradbury R.J.,PO Box 31877 | Cirkovic M.M.,Astronomical Observatory of Belgrade | Dvorsky G.,Institute for Ethics and Emerging Technologies
JBIS - Journal of the British Interplanetary Society | Year: 2011

We critically assess the prevailing currents in the Search for Extraterrestrial Intelligence (SETI), embodied in the notion of radio-searches for intentional artificial signals as envisioned by pioneers such as Frank Drake, Philip Morrison, Michael Papagiannis and others. In particular, we emphasize (1) the necessity of integrating SETI into a wider astrobiological and future studies context, (2) the relevance of and lessons to be learnt from the anti-SETI arguments, in particular Fermi's paradox, and (3) a need for complementary approach which we dub the Dysonian SETI. It is meaningfully derived from the inventive and visionary ideas of Freeman J. Dyson and his imaginative precursors, like Konstantin E. Tsiolkovsky, Olaf Stapledon, Nikola Tesla or John B. S. Haldane, who suggested macro-engineering projects as the focal points in the context of extrapolations about the future of humanity and, by analogy, other intelligent species. We consider practical ramifications of the Dysonian SETI and indicate some of the promising directions for future work.

Wild V.,CNRS Paris Institute of Astrophysics | Wild V.,University of Edinburgh | Charlot S.,CNRS Paris Institute of Astrophysics | Brinchmann J.,Leiden University | And 6 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

We present a systematic study of the shape of the dust attenuation curve in star-forming galaxies from the far-ultraviolet (far-UV) to the near-infrared (NIR; ∼0.15-2μ m), as a function of specific star formation rate (ψS) and axial ratio (b/a), for galaxies with and without a significant bulge. Our sample comprises 23000 (15000) galaxies with a median redshift of 0.07, with photometric entries in the Sloan Digital Sky Survey (SDSS), UKIRT Infrared Deep Sky Survey-Large Area Survey and Galaxy Evolution Explorer-All-Sky Imaging Survey catalogues and emission-line measurements from the SDSS spectroscopic survey. We develop a new pair-matching technique to isolate the dust attenuation curves from the stellar continuum emission. The main results are: (i) the slope of the attenuation curve in the optical varies weakly with ψS, strongly with b/a, and is significantly steeper than the Milky Way extinction law in bulge-dominated galaxies; (ii) the NIR slope is constant and matches the slope of the Milky Way extinction law; (iii) the UV has a slope change consistent with a dust bump at 2175 Å which is evident in all samples and varies strongly in strength with b/a in the bulge-dominated sample; (iv) there is a strong increase in emission-line-to-continuum dust attenuation (τV, line/τV, cont) with both decreasing ψS and increasing b/a; and (v) radial gradients in dust attenuation increase strongly with increasing ψS, and the presence of a bulge does not alter the strength of the gradients. These results are consistent with the picture in which young stars are surrounded by dense 'birth clouds' with low covering factor which disperse on time-scales of ∼107 yr and the diffuse interstellar dust is distributed in a centrally concentrated disc with a smaller scaleheight than the older stars that contribute the majority of the red and NIR light. Within this model, the path-length of diffuse dust, but not of birth-cloud dust, increases with increasing inclination and the apparent optical attenuation curve is steepened by the differential effect of larger dust opacity towards younger stars than towards older stars. Additionally, our findings suggest that: (i) galaxies with higher star formation rates per unit stellar mass have a higher fraction of diffuse dust, which is more centrally concentrated; (ii) the observed strength of the 2175-Å dust feature is affected predominantly by global geometry; and (iii) only highly inclined discs are optically thick. We provide new empirically derived attenuation curves for correcting the light from star-forming galaxies for dust attenuation. © 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Cirkovic M.M.,Astronomical Observatory of Belgrade | Sandberg A.,University of Oxford | Bostrom N.,University of Oxford
Risk Analysis | Year: 2010

We describe a significant practical consequence of taking anthropic biases into account in deriving predictions for rare stochastic catastrophic events. The risks associated with catastrophes such as asteroidal/cometary impacts, supervolcanic episodes, and explosions of supernovae/gamma-ray bursts are based on their observed frequencies. As a result, the frequencies of catastrophes that destroy or are otherwise incompatible with the existence of observers are systematically underestimated. We describe the consequences of this anthropic bias for estimation of catastrophic risks, and suggest some directions for future work. © 2010 Society for Risk Analysis.

Smailagic M.,Astronomical Observatory of Belgrade | Bon E.,Astronomical Observatory of Belgrade
Journal of Astrophysics and Astronomy | Year: 2015

Variability of active galactic nuclei is not well understood. One possible explanation is existence of supermassive binary black holes (SMBBH) in their centres. It is expected that major mergers are common in the Universe. It is expected that each supermassive black hole of every galaxy eventually finish as a SMBBH system in the core of newly formed galaxy. Here we model the emission line profiles of active galactic nuclei (AGN) assuming that the flux and emission line shape variations are induced by supermassive binary black hole systems (SMBBH). We assume that the accreting gas inside the circumbinary (CB) disk is photo ionized by mini accretion disk emission around each SMBBH. We calculate variations of emission line flux, shifts and shapes for different parameters of SMBBH orbits. We consider cases with different masses and inclinations for circular orbits and measure the effect to the shape of emission line profiles and flux variability. © 2015, Indian Academy of Sciences.

Vince O.,Astronomical Observatory of Belgrade
Astronomische Nachrichten | Year: 2010

We use optical color indices (colors) from the SDSS database to study the effect of dust in starburst galaxies by measuring the dependence of colors on galaxy inclination. Starburst galaxies with ongoing star formation, are rich with metals/dust and are, therefore, an excellent objects for studying the effect of dust in galaxies. They are selected using the [O III]λ5007/Hα vs. [N II]λ6584/Hβ diagram, that is, the BPT-diagram. We use Kauffmann's empirical demarcation line in the BPT-diagram to exclude galaxies with active galactic nuclei (AGN) from the sample because they have different physical and dust properties from normal galaxies. The sample is divided into bins according to galaxy stellar mass and 4000 Å break (which is a coarse measure of a galaxy star formation history; SFH) and the reddening with inclination is studied as a function of these two physical parameters. Assuming that the dust effect is negligible in the SDSS z-band, we derive the attenuation curves for these galaxies. We fit the attenuation curves with a simple power law and use power law index to interpret the relative distribution of dust and stars in the starburst galaxies. © 2010 WILEY-VCH Verlag GmbH&Co. KGaA, Weinheim.

Vince O.,Astronomical Observatory of Belgrade
Serbian Astronomical Journal | Year: 2012

Currently, the CCD camera most used by observers of the Astro- nomical Observatory of Belgrade is the ALTA Apogee U42. It is used for both photometric and astrometric observations. Therefore, it is very important to know different measurable parameters which describe the condition of the camera - linearity, gain, readout noise etc. In this paper, we present a thorough test of this camera.

Cirkovic M.M.,Astronomical Observatory of Belgrade | Cirkovic M.M.,University of Oxford
Risk Analysis | Year: 2012

Ought we to take seriously large risks predicted by "exotic" or improbable theories? We routinely assess risks on the basis or either common sense, or some developed theoretical framework based on the best available scientific explanations. Recently, there has been a substantial increase of interest in the low-probability "failure modes" of well-established theories, which can involve global catastrophic risks. However, here I wish to discuss a partially antithetical situation: alternative, low-probability ("small") scientific theories predicting catastrophic outcomes with large probability. I argue that there is an important methodological issue (determining what counts as the best available explanation in cases where the theories involved describe possibilities of extremely destructive global catastrophes), which has been neglected thus far. There is no simple answer to the correct method for dealing with high-probability high-stakes risks following from low-probability theories that still cannot be rejected outright, and much further work is required in this area. I further argue that cases like these are more numerous than usually assumed, for reasons including cognitive biases, sociological issues in science and the media image of science. If that is indeed so, it might lead to a greater weight of these cases in areas such as moral deliberation and policy making. © 2012 Society for Risk Analysis.

Cirkovic M.V.,Astronomical Observatory of Belgrade | Cirkovic M.V.,University of Oxford | Vukotic B.,Astronomical Observatory of Belgrade
International Journal of Astrobiology | Year: 2013

We live in the epoch of explosive development of astrobiology, a novel interdisciplinary field dealing with the origin, evolution and the future of life. The relationship between cosmology and astrobiology is much deeper than it is usually assumed-besides a similarity in the historical model of development of these two disciplines, there is an increasing number of crossover problems and thematic areas which stem from considerations of Copernicanism and observation selection effects. Such a crossover area is both visualized and heuristically strengthened by introduction of the astrobiological landscape, describing complexity of life in the most general context. We argue that this abstract landscape-like structure in the space of astrobiological parameters is a concept capable of unifying different strands of thought and research, a working concept and not only a metaphor. By analogy with phase spaces of complex physical systems, we can understand the astrobiological landscape as a set of viable evolutionary histories of life in a particular region of space. It is a notion complementary to the classical concept of biological morphological space, underscoring the fact that modern astrobiology offers a prospect of both foundational support and vast extension of the domain of applicability of the Darwinian biological evolution. Such a perspective would strengthen foundations upon which various numerical models can be built; the lack of such quantitative models has often been cited as the chief weakness of the entire astrobiological enterprise. © 2012 Cambridge University Press.

Jurkovic M.I.,Astronomical Observatory of Belgrade
EPJ Web of Conferences | Year: 2015

The initial reason for studying Type II Cepheids (CWB) was for period changes, binarity or any other signs of change other than the pulsation. The GCVS contained 71 objects of this kind in 2012 when the wok started, and that list is now extended to 100 CWB and 26 CWB: objects. The photometric data for the 71 objects was collected from ASAS, AAVSO, CATALINA, LINEAR, SuperWASP, NSVS surveys. Surprisingly, there is a discrepancy in the classification of the stars in this list. A large percentage of these objects might not be not Type II Cepheids, some of them are classical Cepheids, RR Lyrae, some eclipsing binaries, there is even a dwarf novae. © Owned by the authors, published by EDP Sciences, 2015.

Cirkovic M.M.,Astronomical Observatory of Belgrade
JBIS - Journal of the British Interplanetary Society | Year: 2016

Advanced Galactic civilizations might, if originally evolved in circumstellar habitable zones of their home planetary systems, occasionally engage in the process Martyn Fogg dubbed "stellification": converting gas giants into stellar objects. There have been several developments since the time of Fogg's original article (1989) which make this astroengineering feat generally appealing. The general concept of stellified substellar objects as a new class of astrophysical sources is introduced. Such sources might, in principle, be detectable from afar, and thus constitute artefacts in the sense of an unorthodox, Dysonian approach to SETI. Therefore, searching for a new kind of astroengineering artefacts - stellified brown dwarfs and giant planets - is warranted.

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