We present an isolated Milky-Way-like simulation in the gadget2
N-body smoothed particle hydrodynamics (SPH) code. The Galactic disc star formation rate (SFR) surface densities and a stellar mass ...indicative of the Solar neighbourhood are used as thresholds to model the distribution of stellar mass in life-friendly environments. SFR and stellar component density are calculated by averaging the gadget2 particle properties on a 2D grid mapped on the Galactic plane. The peak values for possibly habitable stellar mass surface density move from 10 to 15 kpc cylindrical galactocentric distance in a 10-Gyr simulated time span. At 10 Gyr, the simulation results imply the following. Stellar particles that have spent almost all of their lifetime in habitable-friendly conditions typically reside at ∼16 kpc from the Galactic Centre and are ∼3 Gyr old. Stellar particles that have spent ≥90 per cent of their 4–5 Gyr long lifetime in habitable-friendly conditions are also predominantly found in the outskirts of the Galactic disc. Fewer than 1 per cent of these particles can be found at a typical Solar system galactocentric distance of 8–10 kpc. Our results imply that the evolution of an isolated spiral galaxy is likely to result in galactic civilizations emerging at the outskirts of the galactic disc around stellar hosts younger than the Sun.
ABSTRACT
The problem of the extent of habitable zones in different kinds of galaxies is one of the outstanding challenges for contemporary astrobiology. In the present study, we investigate ...habitability in a large sample of simulated galaxies from the illustris Project in order to at least roughly quantify the hospitality to life of different galactic types. The pioneering study of Dayal et al. is critically examined and some of its results are amended. In particular, we find a tentative evidence for a second mode of galactic habitability comprising metal-rich dwarfs similar to IC 225, LMC, or M32. The role of the galactic environment and the observation-selection effects is briefly discussed and prospects for further research on the topic outlined.
•Human enhancement for future space missions is a reasonable option.•Different methods of human enhancement for space include gene editing or implants.•Ethics should support a careful application of ...human enhancement for space missions.
Future human space missions to Mars and beyond may be realized for different research, economic, political or survival reasons. Since space remains a hazardous environment for humans, space exploration and exploitation requires the development and deployment of effective countermeasures. In this paper, we discuss prospects for human enhancement by gene editing, synthetic biology, or implants, for the purposes of future space missions. We argue that there are good reasons to consider such options, and that ethical arguments can be made in favor of human enhancement to enable long-term space exploration.
The Great Silence Cirkovic, Milan M
2018, 2018-04-26, 2018-05-03
eBook
Researchers believe that the universe is vast enough that life has evolved and become technological many times - yet we have seen no trace of extraterrestrial intelligence. This conundrum, known as ...the Fermi pardox, is the deepest mystery in the search for extraterrestrial intelligence. Put simply, where is everybody?.
Astrobiology is an expanding, interdisciplinary field investigating the origin, evolution and future of life in the universe. Tackling many of the foundational debates of the subject, from ...discussions of cosmological evolution to detailed reviews of common concepts such as the 'Rare Earth' hypothesis, this volume is the first systematic survey of the philosophical aspects and conundrums in the study of cosmic life. The author's exploration of the increasing number of cross-over problems highlights the relationship between astrobiology and cosmology and presents some of the challenges of multidisciplinary study. Modern physical theories dealing with the multiverse add a further dimension to the debate. With a selection of beautifully presented illustrations and a strong emphasis on constructing a unified methodology across disciplines, this book will appeal to graduate students and specialists who seek to rectify the fragmented nature of current astrobiological endeavour, as well as curious astrophysicists, biologists and SETI enthusiasts.
Recent studies of Galactic evolution revealed that the dynamics of the stellar component might be one of the key factors when considering galactic habitability. We run an N-body simulation model of ...the Milky Way, which we evolve for 10 Gyr, to study the secular evolution of stellar orbits and the resulting galactic habitability related properties, i.e., the density of the stellar component and close stellar encounters. The results indicate that radial migrations are not negligible, even in a simple axisymmetric model with mild levels of dynamical heating, and that the net outward diffusion of the stellar component can populate galactic outskirts with habitable systems. Habitable environment is also likely even at sub-Solar galactocentric radii, because the rate of close encounters should not significantly degrade habitability. Stars that evolve from non-circular to stable nearly circular orbits typically migrate outwards, settling down in a broad Solar neighbourhood. The region between
$R \approx 3$
kpc and
$R \approx 12$
kpc represents the zone of radial mixing, which can blur the boundaries of the Galactic Habitable Zone (GHZ), as it has been conventionally understood. The present-day stable population of the stars in the Solar neighbourhood originates from this radial mixing zone, with most of the stars coming from the inner regions. The Solar system can be considered as a typical Milky Way habitable system because it migrated outwards from the metal-rich inner regions of the Disk and has a circular orbit in the present epoch. We conclude that the boundaries of the GHZ cannot be sharply confined for a given epoch because of the mixing caused by the stellar migrations and secular evolution of stellar orbits.
Context. Regarding the significant interest in both dark matter and the application of MOND to early-type galaxies, we investigate the MOND theory by comparing its predictions, for models of constant ...mass-to-light ratio, with observational data of the early-type galaxy NGC 4649. Aims. We study whether measurements for NGC 3379 and NGC 1399 are typical of early-type systems and we test the assumption of a Newtonian constant M/L ratio underlying most of the published models. Methods. We employ the globular clusters of NGC 4649 as a mass tracer. The Jeans equation is calculated for both MOND and constant mass-to-light ratio assumptions. Spherical symmetry is assumed and the calculations are performed for both isotropic and anisotropic cases. Results. We found that both Jeans models with the assumption of a constant mass-to-light ratio and different MOND models provide good agreement with the observed values of the velocity dispersion. The most accurate fits of the velocity dispersion were obtained for the mass-to-light ratio in the B-band, which was equal to 7, implying that there is no need for significant amounts of dark matter in the outer parts (beyond 3 effective radii) of this galaxy. We also found that tangential anisotropies are most likely present in NGC 4649.
Cosmology and Hilbert's sixth problem Cirkovic, Milan
Serbian Astronomical Journal/Serbian Astronomical journal,
01/2020, Letnik:
2020, Številka:
200
Journal Article
Odprti dostop
There have been tantalizing indications from many quarters of physical
cosmology that we are living in the multiverse - a huge set of cosmological
domains ("universes"). What is the structure of this ...larger whole is an
entirely open problem on the interface between physics and metaphysics. A
goal of the present paper is to draw attention to the connection between
this problem and an old and celebrated puzzle in mathematical physics. Among
the unresolved problems David Hilbert posed in 1900 as a challenge for the
dawning century, none is more philosophically controversial than the Sixth
Problem, requiring the axiomatization of physical theories. In the new
century and the new millennium, this problem has remained a challenge,
usually swept under the rug as "not belonging to mathematics" (as if that
impacts its epistemical status) or simply "unresolved". Recent radical
ontological/cosmological hypothesis of Max Tegmark, identifying mathematical
and physical structures, might shed some new light onto this allegedly
antiquated subject: it might be the case that the problem has already been
solved, insofar we have formalized mathematical structures! While this can
be seen as "cutting the Gordian knot" rather than patiently resolving the
issue, we suggest that there are several advantages to taking Tegmark's
solution seriously, notably in the domain of (future) physics of the
observer.
Abstract
It is well known that the chances of success of the search for extraterrestrial intelligence depend on the longevity of technological civilizations or, more broadly, on the duration of the ...signs of their existence, or technosignatures. Here, we re-examine this general tenet in more detail, and we show that its broader implications have not been given their proper significance. In particular, an often overlooked aspect is that the duration of a technosignature is in principle almost entirely separable from the age of the civilization that produces it. We propose a classification scheme of technosignatures based on their duration, and we use Monte Carlo simulations to show that, given an initial generic distribution of Galactic technosignatures, only the ones with the longest duration are likely to be detected. This tells us, among other things, that looking for a large number of short-lived technosignatures is a weaker observational strategy than focusing the search on a few long-lived ones. It also suggests abandoning any anthropocentric bias in approaching the question of extraterrestrial intelligence. We finally give some ideas of possible pathways that can lead to the establishment of long-lived technosignatures.
Abstract
In a recent refreshing paper, Cowie (2022, The Philosophical Quarterly) analyses the hypothesis of artificial origin of the mysterious interstellar object 1I/2017 U1 ʻOumuamua, as well as ...the wider question of justification of the artefactual origin explanation for anomalous astronomical phenomena. This highly commendable philosophical project should be further developed in order to establish more general methodology for dealing with traces and manifestations of extraterrestrial intentional actors. In the present note, I demonstrate a couple of weaknesses of the standard account, mainly dealing with philosophy of technology, and suggest ways of improving upon it.
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