2. The Sun’s life-cycle

2020 ◽  
pp. 42-64
Author(s):  
Philip Judge
Keyword(s):  
Life Cycle ◽  
Magnetic Fields ◽  
Main Sequence ◽  
Milky Way ◽  
The Sun ◽  
Centre Of Mass ◽  
Fusion Reactions ◽  
The Past ◽  
Nuclear Fusion Reactions ◽  
The Universe

‘The Sun’s life-cycle’ describes the birth of the Sun out of the debris of stars which exploded early in the life of the Milky Way. When stars form, they employ a disc structure, with matter spinning around the centre of mass like a carousel, aided by magnetic fields. At four and a half million years old, the Sun, like most stars in the Universe, is on the main sequence stage of its life. In this stage, nuclear fusion reactions in its core fuse hydrogen into helium. Both observations and theory infer that the Sun spun faster in the past and was both hotter and less luminous.

The Long View of Planetary Systems

2018 ◽  
Author(s):  
Karel Schrijver
Keyword(s):  
Solar System ◽  
Milky Way ◽  
Planetary Systems ◽  
Giant Planets ◽  
Milky Way Galaxy ◽  
Population Statistics ◽  
The Past ◽  
General Terms ◽  
The Galaxy ◽  
The Universe

How many planetary systems formed before our’s did, and how many will form after? How old is the average exoplanet in the Galaxy? When did the earliest planets start forming? How different are the ages of terrestrial and giant planets? And, ultimately, what will the fate be of our Solar System, of the Milky Way Galaxy, and of the Universe around us? We cannot know the fate of individual exoplanets with great certainty, but based on population statistics this chapter sketches the past, present, and future of exoworlds and of our Earth in general terms.

scholarly journals Small Scale Solar Magnetic Fields: Theory

1977 ◽  
Vol 4 (2) ◽  
pp. 241-250 ◽  
Author(s):  
N. O. Weiss
Keyword(s):  
Magnetic Fields ◽  
Field Strength ◽  
Solar Physics ◽  
Small Scale ◽  
The Sun ◽  
Solar Magnetic Fields ◽  
Solar Granulation ◽  
The Past ◽  
Maximum Field Strength ◽  
Maximum Field

One of the most exciting developments in solar physics over the past eight years has been the success of ground based observers in resolving features with a scale smaller than the solar granulation. In particular, they have demonstrated the existence of intense magnetic fields, with strengths of up to about 1600G. Harvey (1976) has just given an excellent summary of these results.In solar physics, theory generally follows observations. Inter-granular magnetic fields had indeed been expected but their magnitude came as a surprise. Some problems have been discussed in previous reviews (Schmidt, 1968, 1974; Weiss, 1969; Parker, 1976d; Stenflo, 1976) and the new observations have stimulated a flurry of theoretical papers. This review will be limited to the principal problems raised by these filamentary magnetic fields. I shall discuss the interaction of magnetic fields with convection in the sun and attempt to answer such questions as: what is the nature of the equilibrium in a flux tube? how are the fields contained? what determines their stability? how are such strong fields formed and maintained? and what limits the maximum field strength?

scholarly journals A comparison of the density gradients of main sequence stars obtained by two different methods in different galactic latitudes

1970 ◽  
Vol 38 ◽  
pp. 232-235
Author(s):  
W. Becker ◽  
R. Fenkart
Keyword(s):  
Main Sequence ◽  
Milky Way ◽  
Absolute Magnitude ◽  
Galactic Centre ◽  
Density Gradients ◽  
The Sun ◽  
Main Sequence Stars

The Basel Observatory program of the determination of disc- and halo-density gradients for different intervals of absolute magnitude comprises in addition to Milky Way fields several directions, all pointing to Selected Areas near a plane perpendicular to the galactic equator and passing through the sun and the galactic centre. It was started with SA 51 (Becker, 1965) and continued with Sa 57, 54 and 141 (Fenkart, 1967, 1968, 1969).

THE PAST, PRESENT AND FUTURE OF THE SUN'S MAGNETISM

2012 ◽  
Vol 18 ◽  
pp. 130-135
Author(s):  
J. D. DO NASCIMENTO
Keyword(s):  
Magnetic Fields ◽  
Global Scale ◽  
Evolutionary Stage ◽  
The Sun ◽  
Fundamental Parameters ◽  
The Past ◽  
Bona Fide ◽  
The Subject ◽  
Solar Analogs ◽  
Active Investigation

Magnetic field in the Sun is produced through the dynamo process in a way that is not yet completely understood. The question whether the Sun is peculiar as compared with other stars has been the subject of active investigation over the past 5 decades, but no studies have been focused on the properties of rotation and surface magnetic fields. The availability of ESPaDOnS offers an exceptional possibility to study the specificity of rotation and magnetic properties of Sun-like stars by means of spectropolarimetric observations. In this review, we present some results concerning the investigation of magnetic fields and dynamo evolution in cool active solar-like stars. Our results are based on the systematic searching for genuine solar analogs and observation of a sample of bona fide solar twins and solar analogs, whose fundamental parameters and evolutionary stage was determined in our previous studies. Our main aim is to investigate how rotation and magnetism evolve and how the depth of the convection zone may influence the global-scale toroidal magnetic fields at the stellar surface.

scholarly journals Origin of strong magnetic fields in Milky Way-like galaxies

2015 ◽  
Vol 11 (S317) ◽  
pp. 274-275
Author(s):  
Alexander M. Beck
Keyword(s):  
Magnetic Fields ◽  
Galaxy Formation ◽  
Milky Way ◽  
Cosmic Time ◽  
Strong Magnetic Fields ◽  
Origin And Evolution ◽  
The Universe

AbstractMagnetic fields are observed on all scales in the Universe (see e.g. Kronberg 1994), but little is known about the origin and evolution of those fields with cosmic time. Seed fields of arbitrary source must be amplified to present-day values and distributed among cosmic structures. Therefore, the emergence of cosmic magnetic fields and corresponding dynamo processes (see e.g. Zel'dovich et al. 1983; Kulsrud et al. 1997) can only be jointly understood with the very basic processes of structure and galaxy formation (see e.g. Mo et al. 2010).

scholarly journals The Gaia-ESO Survey: Churning through the Milky Way

2018 ◽  
Vol 609 ◽  
pp. A79 ◽  
Author(s):  
M. R. Hayden ◽  
A. Recio-Blanco ◽  
P. de Laverny ◽  
S. Mikolaitis ◽  
G. Guiglion ◽  
...  
Keyword(s):  
Milky Way ◽  
Past History ◽  
Stellar Populations ◽  
Solar Neighborhood ◽  
The Sun ◽  
Radial Migration ◽  
Orbital Parameters ◽  
The Past ◽  
Major Merger ◽  
History Of

Context. There have been conflicting results with respect to the extent that radial migration has played in the evolution of the Galaxy. Additionally, observations of the solar neighborhood have shown evidence of a merger in the past history of the Milky Way that drives enhanced radial migration. Aims. We attempt to determine the relative fraction of stars that have undergone significant radial migration by studying the orbital properties of metal-rich ([Fe/H] > 0.1) stars within 2 kpc of the Sun. We also aim to investigate the kinematic properties, such as velocity dispersion and orbital parameters, of stellar populations near the Sun as a function of [Mg/Fe] and [Fe/H], which could show evidence of a major merger in the past history of the Milky Way. Methods. We used a sample of more than 3000 stars selected from the fourth internal data release of the Gaia-ESO Survey. We used the stellar parameters from the Gaia-ESO Survey along with proper motions from PPMXL to determine distances, kinematics, and orbital properties for these stars to analyze the chemodynamic properties of stellar populations near the Sun. Results. Analyzing the kinematics of the most metal-rich stars ([Fe/H] > 0.1), we find that more than half have small eccentricities (e< 0.2) or are on nearly circular orbits. Slightly more than 20% of the metal-rich stars have perigalacticons Rp> 7 kpc. We find that the highest [Mg/Fe], metal-poor populations have lower vertical and radial velocity dispersions compared to lower [Mg/Fe] populations of similar metallicity by ~10 km s-1. The median eccentricity increases linearly with [Mg/Fe] across all metallicities, while the perigalacticon decreases with increasing [Mg/Fe] for all metallicities. Finally, the most [Mg/Fe]-rich stars are found to have significant asymmetric drift and rotate more than 40 km s-1 slower than stars with lower [Mg/Fe] ratios. Conclusions. While our results cannot constrain how far stars have migrated, we propose that migration processes are likely to have played an important role in the evolution of the Milky Way, with metal-rich stars migrating from the inner disk toward to solar neighborhood and past mergers potentially driving enhanced migration of older stellar populations in the disk.

4. What are planets made of?

2021 ◽  
pp. 47-75
Author(s):  
Raymond T. Pierrehumbert
Keyword(s):  
Life Cycle ◽  
Solar System ◽  
Milky Way ◽  
Planetary Systems ◽  
Big Bang ◽  
Heavy Elements ◽  
Milky Way Galaxy ◽  
First Stars ◽  
The Big Bang ◽  
The Universe

‘What are planets made of?’ assesses what planets are made of, beginning by looking at the life cycle of stars, and the kinds of stars which populate the Universe. Although the first stars of the Universe could not have formed planetary systems, the process did not take long to get under way. The Milky Way galaxy formed not long after the Big Bang and has been building its stock of heavy elements ever since. Thus, our Solar System incorporates ingredients from a mix of myriad expired stars, most of which have been processed multiple times through short-lived stars.

scholarly journals Cosmic magnetic field observations with next generation instrumentation

2009 ◽  
Vol 5 (H15) ◽  
pp. 430-431
Author(s):  
Rainer Beck
Keyword(s):  
Magnetic Fields ◽  
Milky Way ◽  
Low Frequency ◽  
Radio Telescopes ◽  
Radio Waves ◽  
Huge Number ◽  
Fundamental Physics ◽  
New Era ◽  
Weak Magnetic Fields ◽  
The Universe

AbstractThe origin of magnetic fields in the Universe is an open problem in astrophysics and fundamental physics. Forthcoming radio telescopes will open a new era in studying cosmic magnetic fields. Low-frequency radio waves will reveal the structure of weak magnetic fields in the outer regions and halos of galaxies and in intracluster media. At higher frequencies, the EVLA and the SKA will map the structure of magnetic fields in galaxies in unprecedented detail. All-sky surveys of Faraday rotation measures (RM) towards a huge number of polarized background sources with the SKA and its pathfinders will allow us to model the structure and strength of the regular magnetic fields in the Milky Way, the interstellar medium of galaxies, in galaxy clusters and the intergalactic medium.

Introductory remarks

1994 ◽  
Vol 346 (1678) ◽  
pp. 1-2 ◽  
Keyword(s):  
Gamma Rays ◽  
Gamma Ray ◽  
Neutrino Flux ◽  
The Sun ◽  
Gamma Ray Astronomy ◽  
The Past ◽  
The Subject ◽  
Neutrino Astronomy ◽  
The Universe ◽  
Particle Physicist

Nearly twenty years ago, G. D. Rochester and I organized a Discussion Meeting here on the origin of the cosmic radiation. P art of that meeting was devoted to primary gamma rays, and this meeting was followed a few years later by a meeting devoted entirely to gamma ray astronomy. At that time gamma rays represented a ‘new window on the Universe’. Now it is the turn of neutrinos to move into that slot, although it must be said that neutrino astronomy is not as far on as gamma ray astronomy was at that stage. Nevertheless, the subject has started and has already thrown up some dramatic questions, questions of interest to both astronomer and elementary particle physicist. In the more conventional astronomies, the Sun appears to be quite well behaved, and reasonably understood, with the interests of many centring on more distant and ‘dramatic’ objects, such as supernovae and extragalactic sources. With neutrinos, however, supernovae seem to be well behaved — at the superficial level, at least and based on one event — but the Sun does not. The remarkable deficit in solar neutrino flux recorded by Davis and collaborators over the past decades has been confirmed and we look forward to hearing the details of these confirmations, as well as the energy dependence of the flux and its comparison with expectation.

scholarly journals Study of the effects of magnetic braking on the lithium abundances of the Sun and solar-type stars

2020 ◽  
Vol 496 (2) ◽  
pp. 1343-1354
Author(s):  
R Caballero Navarro ◽  
A García Hernández ◽  
A Ayala ◽  
J C Suárez
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Globular Clusters ◽  
Main Sequence ◽  
The Sun ◽  
Depletion Rate ◽  
Solar Type ◽  
Magnetic Braking ◽  
Physical Phenomena ◽  
The Impact

ABSTRACT The study of lithium (Li) surface abundance in the Sun and young stellar globular clusters which are seemingly anomalous in present-day scenarios, as well as the influence of rotation and magnetic braking (MB) on its depletion during pre-main sequence (PMS) and main sequence (MS). In this work, the effects of rotational mixing and of the rotational hydrostatic effects on Li abundances are studied by simulating several grids of PMS and MS rotating and non-rotating models. Those effects are combined with the additional impact of the MB (with magnetic field intensities ranging between 3.0 and 5.0 G). The data obtained from simulations are confronted by comparing different stellar parameters. The results show that the surface Li abundance for the Sun-like models at the end of the PMS and throughout the MS decreases when rotational effects are included, that is the Li depletion rate for rotating models is higher than for non-rotating ones. This effect is attenuated when the MB produced by a magnetic field is present. This physical phenomena impacts also the star effective temperature (Teff) and its location in the HR diagram. The impact of MB in Li depletion is sensitive to the magnetic field intensity: the higher it is, the lower the Li destruction. A direct link between the magnetic fields and the convective zone (CZ) size is observed: stronger magnetic fields produce shallower CZ’s. This result suggests that MB effect must be taken into consideration during PMS if we aim to reproduce Li abundances in young clusters.

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