scholarly journals Exploring the origin of low-metallicity stars in Milky-Way-like galaxies with the NIHAO-UHD simulations

2020 ◽  
Vol 500 (3) ◽  
pp. 3750-3762
Author(s):  
Federico Sestito ◽  
Tobias Buck ◽  
Else Starkenburg ◽  
Nicolas F Martin ◽  
Julio F Navarro ◽  
...  
Keyword(s):  
High Resolution ◽  
Milky Way ◽  
Large Population ◽  
Big Bang ◽  
The Other ◽  
Cosmic Evolution ◽  
Early Formation ◽  
History Of ◽  
Low Metallicity ◽  
The Big Bang

ABSTRACT The kinematics of the most metal-poor stars provide a window into the early formation and accretion history of the Milky Way (MW). Here, we use five high-resolution cosmological zoom-in simulations (∼ 5 × 106 star particles) of MW-like galaxies taken from the NIHAO-UHD project, to investigate the origin of low-metallicity stars ([Fe/H] ≤ −2.5). The simulations show a prominent population of low-metallicity stars confined to the disc plane, as recently discovered in the MW. The ubiquity of this finding suggests that the MW is not unique in this respect. Independently of the accretion history, we find that ≳90 per cent of the retrograde stars in this population are brought in during the initial build-up of the galaxies during the first few Gyr after the Big Bang. Our results therefore highlight the great potential of the retrograde population as a tracer of the early build-up of the MW. The prograde planar population, on the other hand, is accreted during the later assembly phase and samples the full galactic accretion history. In case of a quiet accretion history, this prograde population is mainly brought in during the first half of cosmic evolution (t ≲ 7 Gyr), while, in the case of an ongoing active accretion history, later mergers on prograde orbits are also able to contribute to this population. Finally, we note that the MW shows a rather large population of eccentric, very metal-poor planar stars. This is a feature not seen in most of our simulations, with the exception of one simulation with an exceptionally active early building phase.

scholarly journals Li isotopes in metal-poor halo dwarfs: a more and more complicated story

2009 ◽  
Vol 5 (S268) ◽  
pp. 201-210
Author(s):  
Monique Spite ◽  
François Spite
Keyword(s):  
Cosmic Rays ◽  
Big Bang ◽  
The Other ◽  
Big Bang Nucleosynthesis ◽  
Lithium Abundance ◽  
The Galaxy ◽  
Li Isotope ◽  
Low Metallicity ◽  
The Big Bang ◽  
Early Galaxy

AbstractThe nuclei of the lithium isotopes are fragile, easily destroyed, so that, at variance with most of the other elements, they cannot be formed in stars through steady hydrostatic nucleosynthesis.The 7Li isotope is synthesized during primordial nucleosynthesis in the first minutes after the Big Bang and later by cosmic rays, by novae and in pulsations of AGB stars (possibly also by the ν process). 6Li is mainly formed by cosmic rays. The oldest (most metal-deficient) warm galactic stars should retain the signature of these processes if, (as it had been often expected) lithium is not depleted in these stars. The existence of a “plateau” of the abundance of 7Li (and of its slope) in the warm metal-poor stars is discussed. At very low metallicity ([Fe/H] < −2.7dex) the star to star scatter increases significantly towards low Li abundances. The highest value of the lithium abundance in the early stellar matter of the Galaxy (logϵ(Li) = A(7Li) = 2.2 dex) is much lower than the the value (logϵ(Li) = 2.72) predicted by the standard Big Bang nucleosynthesis, according to the specifications found by the satellite WMAP. After gathering a homogeneous stellar sample, and analysing its behaviour, possible explanations of the disagreement between Big Bang and stellar abundances are discussed (including early astration and diffusion). On the other hand, possibilities of lower productions of 7Li in the standard and/or non-standard Big Bang nucleosyntheses are briefly evoked.A surprisingly high value (A(6Li)=0.8 dex) of the abundance of the 6Li isotope has been found in a few warm metal-poor stars. Such a high abundance of 6Li independent of the mean metallicity in the early Galaxy cannot be easily explained. But are we really observing 6Li?

scholarly journals The Radiation-Dominated Universe in Nonstandard Cosmology

2020 ◽  
Vol 5 (4) ◽  
Author(s):  
Günter Scharf ◽  
Keyword(s):  
Evolution Equations ◽  
Big Bang ◽  
The Other ◽  
Spherically Symmetric ◽  
Velocity Perturbation ◽  
Model Universe ◽  
Cosmic Evolution ◽  
Big Crunch ◽  
The Big Bang ◽  
Irregular Singular Points

We continue the recent study of our model theory of low-density cosmology without dark matter. We assume a purely radiative spherically symmetric background and treat matter as anisotropic perturbations. Einstein’s equations for the background are solved numerically. We find two irregular singular points, one is the Big Bang and the other a Big Crunch. The radiation temperature continues to decrease for another 0.21 Hubble times and then starts to increase towards infinity. Then we derive the four evolution equations for the anisotropic perturbations. In the Regge- Wheeler gauge there are three metric perturbations and a radial velocity perturbation. The solution of these equations allow a detailed discussion of the cosmic evolution of the model universe under study.

scholarly journals Reconstructing the Cosmic Evolution of the Chemical Elements

Daedalus ◽  
2014 ◽  
Vol 143 (4) ◽  
pp. 71-80 ◽  
Author(s):  
Anna Frebel
Keyword(s):  
Chemical Analysis ◽  
Chemical Evolution ◽  
Milky Way ◽  
Chemical Elements ◽  
Big Bang ◽  
First Stars ◽  
Dense Cores ◽  
Cosmic Evolution ◽  
Supernova Explosions ◽  
The Big Bang

The chemical elements are created in nuclear fusion processes in the hot and dense cores of stars. The energy generated through nucleosynthesis allows stars to shine for billions of years. When these stars explode as massive supernovae, the newly made elements are expelled, chemically enriching the surrounding regions. Subsequent generations of stars are formed from gas that is slightly more element-enriched than that from which previous stars formed. This chemical evolution can be traced back to its beginning soon after the Big Bang by studying the oldest and most metal-poor stars still observable in the Milky Way today. Through chemical analysis, they provide the only available tool for gaining information about the nature of the short-lived first stars and their supernova explosions more than thirteen billion years ago. These events set in motion the transformation of the pristine universe into a rich cosmos of chemically diverse planets, stars, and galaxies.

scholarly journals FRONTIER RESEARCH IN ASTROPHYSICS IN THE GRAVITATIONAL WAVE ERA - II(EXOPLANETS AND EMERGENCE OF LIFE)

2021 ◽  
Vol 53 ◽  
pp. 235-244
Author(s):  
L. Sabau-Graziati ◽  
F. Giovannelli
Keyword(s):  
Gravitational Wave ◽  
Milky Way ◽  
Big Bang ◽  
Habitable Zone ◽  
Terrestrial Life ◽  
The Big Bang ◽  
Emergence Of Life

In this paper we will discuss exoplanets in the habitable zone of the Milky Way, the origin of terrestrial life, and what 'intelligent' humanity is doing, in order to complete the excursion on <i>The Bridge between the Big Bang and Biology</i>, started with the paper I (Giovannelli & Sabau-Graziati, 2020).

scholarly journals From cosmos to intelligent life: the four ages of astrobiology

2012 ◽  
Vol 11 (4) ◽  
pp. 345-350 ◽  
Author(s):  
Marcelo Gleiser
Keyword(s):  
Chemical Elements ◽  
Life Forms ◽  
Big Bang ◽  
Self Awareness ◽  
First Stars ◽  
History Of ◽  
Life On Earth ◽  
The Big Bang ◽  
The Universe ◽  
Intelligent Life

AbstractThe history of life on Earth and in other potential life-bearing planetary platforms is deeply linked to the history of the Universe. Since life, as we know, relies on chemical elements forged in dying heavy stars, the Universe needs to be old enough for stars to form and evolve. The current cosmological theory indicates that the Universe is 13.7 ± 0.13 billion years old and that the first stars formed hundreds of millions of years after the Big Bang. At least some stars formed with stable planetary systems wherein a set of biochemical reactions leading to life could have taken place. In this paper, I argue that we can divide cosmological history into four ages, from the Big Bang to intelligent life. The physical age describes the origin of the Universe, of matter, of cosmic nucleosynthesis, as well as the formation of the first stars and Galaxies. The chemical age began when heavy stars provided the raw ingredients for life through stellar nucleosynthesis and describes how heavier chemical elements collected in nascent planets and Moons gave rise to prebiotic biomolecules. The biological age describes the origin of early life, its evolution through Darwinian natural selection and the emergence of complex multicellular life forms. Finally, the cognitive age describes how complex life evolved into intelligent life capable of self-awareness and of developing technology through the directed manipulation of energy and materials. I conclude discussing whether we are the rule or the exception.

scholarly journals Repackaging Popular Culture: Commentary and Critique in Community

2012 ◽  
Vol 5 (2) ◽  
Author(s):  
Tully Barnett ◽  
Ben Kooyman
Keyword(s):  
Popular Culture ◽  
Science Fiction ◽  
Everyday Life ◽  
Pop Culture ◽  
Big Bang ◽  
Fan Culture ◽  
High Stakes ◽  
History Of ◽  
Nerd Culture ◽  
The Big Bang

Contemporaneous with the collision of Science Fiction/Fantasy with the mainstream evident in the success of nerd culture show The Big Bang Theory (2007- ), Joss Whedon’s The Avengers (2012), the growth of Comic Con audiences and so on, Dan Harmon developed Community (2009- ), a sitcom depicting a study group at a second-rate community college. The show exemplifies a recent gravitation away from the multi-camera, laugh-track driven sitcom formula, alternating between “straight” episodes dealing with traditional sitcom premises, though always inflected with self-aware acumen, and more ambitious, unconventional episodes featuring outlandish premises, often infused with the trappings of genre and geek fandom. The show presents apocalyptic action- and Western-style paintball wars, epidemics that evoke zombie cinema, a Yahtzee game that spirals into alternate timelines, and a high-stakes Dungeons and Dragons game that blurs the boundaries between reality and fantasy.  Both the straight and the unconventional episodes ultimately serve the same purpose, examining the intersection between nerd culture and everyday life. This essay discusses a number of episodes which exemplify Community’s intersections between everyday life and popular culture, charting the show’s evolving preoccupation with pop culture and intertwining of reality and fantasy. It discusses Community’s self-referentiality as a sitcom, its ambitious and elaborate recreations of and homages to pop culture artefacts, and its explicit gravitation towards Science Fiction and Telefantasy in its third season. Through its various homages to popular culture and ongoing depiction of fan culture, we posit that the show is both a work of fandom and a work about fandom, advocating for the pivotal role of fandom in everyday life and for popular culture as a tool for interpreting, comprehending and navigating life. In this respect, the show contributes to the long history of both the sitcom and Telefantasy as vehicles for cultural commentary.

scholarly journals Quasi-Steady State Cosmology

1994 ◽  
Vol 159 ◽  
pp. 293-299
Author(s):  
G. Burbidge ◽  
F. Hoyle ◽  
J.V. Narlikar
Keyword(s):  
Steady State ◽  
Early Universe ◽  
Particle Physics ◽  
Physical Theory ◽  
Big Bang ◽  
Quasi Steady State ◽  
Recent Developments ◽  
History Of ◽  
The Big Bang ◽  
The Universe

The standard big bang cosmology has the universe created out of a primeval explosion that not only created matter and radiation but also spacetime itself. The big bang event itself cannot be discussed within the framework of a physical theory but the events following it are in principle considered within the scope of science. The recent developments on the frontier between particle physics and cosmology highlight the attempts to chart the history of the very early universe.

More Reflections

Tempo ◽  
1983 ◽  
pp. 12-14
Author(s):  
Robert Simpson
Keyword(s):  
Big Bang ◽  
The Other ◽  
Central Axis ◽  
Apparent Absence ◽  
Actual Experience ◽  
Gravitational Pull ◽  
The Big Bang ◽  
The Universe

Any imaginative hypothesis must be seminal, and Jonathan Harvey's is no exception. As he points out, a number of composers have been fascinated by the idea of harmonic structures radiating above and below a central axis in reflecting intervals. He says ‘from either side’ rather than ‘above and below’, and perhaps advisedly, for as soon as the concept of ‘below’ is permitted, so is that of gravity. The thesis depends on the removal of gravity in what is essentially a placeless, directionless space, without perceptible ups, downs, or sides. Swedenborg's rarified and not altogether realistic ideas come from a mysticism that is unclear about the nature of space. There are relative directions in space; it has dimensions; it is full of energy and radiation; in it gravity is inescapable. A man floating between earth and moon may not be aware of it, but he will drift in one direction or the other, according to which gravitational pull is the stronger. We can estimate at least roughly the distances between the galaxies, and their relative positions, their rates of movement away from each other if they do not belong to the same group. If the theory that in music the bass has moved to the middle refers to the apparent absence of an absolute bottom to the universe, it can be regarded as at least plausible, though without much basis in actual experience, and scarcely susceptible to proof. Where is this axis from which things radiate? It is not, presumably, a fixed and all too audible persistent internal pedal. No doubt it was there at the beginning, like the Big Bang, to be afterwards detected only by means of some residual musical radiation. It becomes an imaginary, or remembered, point.

scholarly journals Connecting cosmological simulations to the real world

2003 ◽  
Vol 208 ◽  
pp. 245-260
Author(s):  
C.S. Frenk
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Big Bang ◽  
Accelerated Expansion ◽  
Astronomical Data ◽  
Cosmic Evolution ◽  
Small Quantum ◽  
The Big Bang ◽  
Current Paradigm ◽  
Coherent Picture

A timely combination of new theoretical ideas and observational discoveries has brought about significant advances in our understanding of cosmic evolution. Computer simulations have played a key role in these developments by providing the means to interpret astronomical data in the context of physical and cosmological theory. In the current paradigm, our Universe has a flat geometry, is undergoing accelerated expansion and is gravitationaly dominated by elementary particles that make up cold dark matter. Within this framework, it is possible to simulate in a computer the emergence of galaxies and other structures from small quantum fluctuations imprinted during an epoch of inflationary expansion shortly after the Big Bang. The simulations must take into account the evolution of the dark matter as well as the gaseous processes involved in the formation of stars and other visible components. Although many unresolved questions remain, a coherent picture for the formation of cosmic structure in now beginning to emerge.

Sign in / Sign up

Export Citation Format

Share Document