scholarly journals Possible Constituents of Halos

1987 ◽  
Vol 117 ◽  
pp. 395-409
Author(s):  
Martin J. Rees
Keyword(s):  
Galaxy Formation ◽  
Massive Stars ◽  
Critical Density ◽  
Big Bang ◽  
Galactic Halos ◽  
Low Mass Stars ◽  
Groups Of Galaxies ◽  
Low Mass ◽  
The Big Bang ◽  
The Universe

There still seem to be three serious contenders for the dark matter in galactic halos and groups of galaxies: (i) very low mass stars, (ii) black hole remnants of very massive stars or (iii) some species of particle (e.g. axions, photinos, etc.) surviving from the big bang. There are genuine prospects of detecting individual objects in all three of these categories, and thereby narrowing down the present range of options. If the Universe has the critical density (Ω = 1), rather than the lower value (Ω = 0.1–0.2) inferred from dynamical evidence, then the galaxies must be more clustered than the overall distribution even on scales 10–20 Mpc. “Biased” galaxy formation could account for this.

The First Stars

2013 ◽  
Author(s):  
Abraham Loeb ◽  
Steven R. Furlanetto
Keyword(s):  
Phase Transition ◽  
Early Universe ◽  
Galaxy Formation ◽  
Big Bang ◽  
First Stars ◽  
Complex Chemical ◽  
Radiative Processes ◽  
Complex Processes ◽  
The Big Bang ◽  
The Universe

This chapter considers the emergence of the complex chemical and radiative processes during the first stages of galaxy formation. It studies the appearance of the first stars, their feedback processes, and the resulting ionization structures that emerged during and shortly after the cosmic dawn. The formation of the first stars tens or hundreds of millions of years after the Big Bang had marked a crucial transition in the early Universe. Before this point, the Universe was elegantly described by a small number of parameters. But as soon as the first stars formed, more complex processes entered the scene. To illustrate this, the chapter provides a brief outline of the prevailing (though observationally untested) theory for this cosmological phase transition.

scholarly journals Joint Discussion 10: 3D views on cool stellar atmospheres – theory meets observation

2009 ◽  
Vol 5 (H15) ◽  
pp. 331-343
Author(s):  
K.N. Nagendra ◽  
P. Bonifacio ◽  
H.-G. Ludwig
Keyword(s):  
Chemical Composition ◽  
High Efficiency ◽  
Big Bang ◽  
Stellar Atmosphere ◽  
Stellar Atmospheres ◽  
Stellar Spectra ◽  
Low Mass ◽  
Computational Resources ◽  
The Big Bang ◽  
The Universe

Much of what we know about the chemical composition of the Universe actually stems from the chemical composition of stars, which is often deciphered from the spectra emerging from their atmospheres. Cool, low-mass and long-living stars allow to study the evolution of the Universe's chemistry from a time shortly after the big bang until today. The observation and interpretation of stellar spectra is a classical field in astronomy but is still undergoing vivid developments. The enormous increase in available computational resources opened-up possibilities which led to a revolution in the degree of realism to which modelers can mimic Nature. High-resolution, high-stability, high-efficiency spectrographs are now routinely providing stellar spectra whose full information content can only be exploited if a very much refined description of a stellar atmosphere is at hand.

scholarly journals Probing the Cosmic Frontier of Galaxies

2015 ◽  
Vol 11 (A29B) ◽  
pp. 808-811
Author(s):  
Pascal A. Oesch
Keyword(s):  
Galaxy Formation ◽  
Mass Density ◽  
Formation Rate ◽  
Big Bang ◽  
Ir Camera ◽  
Blank Field ◽  
Open Questions ◽  
First Galaxies ◽  
The Big Bang ◽  
The Universe

AbstractUnderstanding when and how the first galaxies formed and what sources reionized the universe are key goals of extragalactic astronomy. Thanks to deep surveys with the powerful WFC3/IR camera on the HST, the observational frontier of galaxy build-up now lies at only ~450 Myr after the Big Bang, at redshifts z ~10-12. In combination with deep data from Spitzer/IRAC we can now probe the evolution of the stellar mass density over 96% of cosmic history. However, detecting and characterizing galaxies at these early epochs is challenging even for HST and the sample sizes at the earliest redshifts are still very small. The Hubble Frontier Fields provide a prime new dataset to improve upon our current, sparse sampling of the UV luminosity function at z>8 from blank fields to answer some of the most pressing open questions. For instance, even the evolution of the cosmic star-formation rate density at z>8 is still debated. While our measurements based on blank field data indicate that galaxies with SFR>0.7 Msol/yr disappear quickly from the cosmic record between z~8 and z~10, other previous results, e.g., from the CLASH survey favor a more moderate decline. Here, we briefly review the recent progress in studying galaxy build-up out to z~10 from the combined blank field and existing Frontier Field datasets and discuss their implications for primordial galaxy formation and cosmic reionization.

Cosmology

2017 ◽  
Author(s):  
Nicholas Manton ◽  
Nicholas Mee
Keyword(s):  
Galaxy Formation ◽  
Large Scale ◽  
Cosmological Parameters ◽  
Big Bang ◽  
Newtonian Gravity ◽  
Microwave Background ◽  
Cosmological Redshift ◽  
Frw Model ◽  
The Big Bang ◽  
The Universe

This chapter is about the large-scale structure of the universe, how it is described in general relativity and recent advances in determining the cosmological parameters. The Hubble distance–redshift relationship is discussed. The assumptions of the FRW cosmologies are presented and the FRW solutions of Einstein equation are derived. The FRW model is interpreted in terms of Newtonian gravity. Cosmological redshift is explained. The evidence for dark matter and its possible origin are discussed. The evidence for the Big Bang is presented, including the cosmic microwave background and the latest measurements of the CMB by the Planck probe. The evidence for dark energy is discussed, along with its interpretation as an FRW cosmology with a non-zero cosmological constant. Computer models of galaxy formation are discussed. Outstanding cosmological puzzles are presented along with their possible solution by inflationary models.

Linear Growth of Cosmological Perturbations

2013 ◽  
Author(s):  
Abraham Loeb ◽  
Steven R. Furlanetto
Keyword(s):  
Galaxy Formation ◽  
Big Bang ◽  
Density Fluctuations ◽  
Microwave Background ◽  
Cosmological Recombination ◽  
Small Density ◽  
Evolution Of Structure ◽  
First Galaxies ◽  
The Big Bang ◽  
The Universe

This chapter shows that, after cosmological recombination, the Universe had entered the “dark ages,” during which the relic cosmic microwave background (CMB) light from the Big Bang gradually faded away. During this “pregnancy” period (which lasted hundreds of millions of years), the seeds of small density fluctuations planted by inflation in the matter distribution grew until they eventually collapsed to make the first galaxies. In addition to the density evolution, the second key “initial condition” for galaxy formation is the temperature of the hydrogen and helium gas that had likewise collapsed into the first galaxies. Here, the chapter describes the first stages of these processes and introduces the methods conventionally used to describe the fluctuations. It follows the evolution of structure in the linear regime, when the perturbations are small.

scholarly journals Joint Discussion 7 The Universe at zz>6

2006 ◽  
Vol 2 (14) ◽  
pp. 245-245
Author(s):  
Daniel Schaerer ◽  
Andrea Ferrara (eds)
Keyword(s):  
Galaxy Formation ◽  
Big Bang ◽  
First Stars ◽  
Dark Ages ◽  
Important Challenge ◽  
The Big Bang ◽  
The Universe

The exploration of the earliest phase of star and galaxy formation after the Big Bang remains an important challenge of contemporary astrophysics and represents a key science driver for numerous future facilities. During this phase the first stars and galaxies appear and start to light up and ionize the then neutral Universe ending thereby the so called cosmic dark ages and leading progressively to the complete reionization we observe now at redshift z≃6 or earlier.

scholarly journals The limits of cosmology: role of the Moon

2020 ◽  
Vol 379 (2188) ◽  
pp. 20190561 ◽  
Author(s):  
Joseph Silk
Keyword(s):  
Galaxy Formation ◽  
Star Clusters ◽  
Far Infrared ◽  
Big Bang ◽  
Habitable Zone ◽  
The Moon ◽  
The Big Bang ◽  
The Universe ◽  
Infrared Telescopes

The lunar surface allows a unique way forward in cosmology, to go beyond current limits. The far side provides an unexcelled radio-quiet environment for probing the dark ages via 21 cm interferometry to seek elusive clues on the nature of the infinitesimal fluctuations that seeded galaxy formation. Far-infrared telescopes in cold and dark lunar polar craters will probe back to the first months of the Big Bang and study associated spectral distortions in the CMB. Optical and IR megatelescopes will image the first star clusters in the Universe and seek biosignatures in the atmospheres of unprecedented numbers of nearby habitable zone exoplanets. The goals are compelling and a stable lunar platform will enable construction of telescopes that can access trillions of modes in the sky, providing the key to exploration of our cosmic origins. This article is part of a discussion meeting issue ‘Astronomy from the Moon: the next decades’.

scholarly journals Evolution of D and 3He in the Galaxy

2000 ◽  
Vol 198 ◽  
pp. 525-534 ◽  
Author(s):  
Monica Tosi
Keyword(s):  
Big Bang ◽  
Isotopic Ratios ◽  
Galactic Chemical Evolution ◽  
Low Mass Stars ◽  
Carbon Isotopic ◽  
The Galaxy ◽  
Low Mass ◽  
Red Giant ◽  
The Big Bang ◽  
Self Consistency

The predictions of Galactic chemical evolution models for D and 3He are described in connection with those on the other Galactic quantities for which observational constraints are available.Models in agreement with the largest set of data predict deuterium depletions from the Big Bang to the present epoch smaller than a factor of 3 and do not allow for D/H primordial abundances larger than ∼ 4 × 10—5. Models predicting higher D consumption do not reproduce other observed features of our Galaxy.If both the primordial D and 3He are low, models assuming that 90% of low-mass stars experience an extra-mixing during the red giant phase reproduce all the 3He observed abundances. The same percentage allows to fit also the observed carbon isotopic ratios, thus supporting the self-consistency of the extra-mixing mechanism.

What is the dark matter in galactic halos and clusters?

1986 ◽  
Vol 320 (1556) ◽  
pp. 573-583
Keyword(s):  
Black Holes ◽  
Dark Matter ◽  
Early Universe ◽  
Massive Stars ◽  
Galactic Halos ◽  
Early Generation ◽  
Low Mass Stars ◽  
Low Mass

The dark matter in galactic halos and clusters could be very faint low-mass stars, or in black holes (the remnants of an early generation of very massive stars); alternatively, it could be some species of particle surviving from the early Universe. Although none of these three very different possibilities can yet be excluded, there are real prospects that observations and experiments may soon allow us to discriminate among them. The dynamically inferred dark matter contributes a fraction Ω = 0.1-0.2 of the critical cosmological density. The problem of reconciling the data with the theoretically appealing hypothesis that Ω = 1 is briefly addressed.

scholarly journals Massive star archeology in globular clusters

2014 ◽  
Vol 9 (S307) ◽  
pp. 96-97
Author(s):  
W. Chantereau ◽  
C. Charbonnel ◽  
G. Meynet
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Massive Star ◽  
Massive Stars ◽  
Hot Stars ◽  
Low Mass Stars ◽  
Multiple Populations ◽  
Long Time ◽  
Low Mass ◽  
The Universe

AbstractGlobular clusters are among the oldest structures in the Universe and they host today low-mass stars and no gas. However, there has been a time when they formed as gaseous objects hosting a large number of short-lived, massive stars. Many details on this early epoch have been depicted recently through unprecedented dissection of low-mass globular cluster stars via spectroscopy and photometry. In particular, multiple populations have been identified, which bear the nucleosynthetic fingerprints of the massive hot stars disappeared a long time ago. Here we discuss how massive star archeology can be done through the lense of these multiple populations.

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