scholarly journals The galactic magnetic field derived from cosmic-ray electrons

1968 ◽  
Vol 46 (10) ◽  
pp. S642-S645 ◽  
Author(s):  
H. Okuda ◽  
Y. Tanaka
Keyword(s):  
Magnetic Field ◽  
Solar System ◽  
Electron Spectrum ◽  
Galactic Center ◽  
Galactic Disk ◽  
Cosmic Ray ◽  
Field Configuration ◽  
Galactic Magnetic Field ◽  
Upper Limits ◽  
The Magnetic Field

An estimate of the galactic magnetic field is obtained by combining new results in the cosmic-ray electron spectrum and the recent radio data. The lower and upper limits of the magnetic field in the galactic disk are derived from two alternative models of field configuration; i.e. (0.5–1.0) × 10−5 gauss near the solar system and (1.0–2.0) × 10−5 gauss near the galactic center, respectively. The magnetic field in the halo is estimated to be larger than 2.5 × 10−6 gauss.

scholarly journals Cosmic ray driven dynamo in barred and ringed galaxies

2010 ◽  
Vol 6 (S274) ◽  
pp. 398-400
Author(s):  
K. Kulpa-Dybeł ◽  
K. Otmianowska-Mazur ◽  
B. Kulesza-Żydzik ◽  
G. Kowal ◽  
D. Wóltański ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Radio Emission ◽  
High Frequency ◽  
Galactic Disk ◽  
Cosmic Ray ◽  
Field Configuration ◽  
Magnetic Field Configuration ◽  
Global Evolution ◽  
Weak Magnetic Fields ◽  
The Magnetic Field

AbstractWe study the global evolution of the magnetic field and interstellar medium (ISM) of the barred and ringed galaxies in the presence of non-axisymmetric components of the potential, i.e. the bar and/or the oval perturbations. The magnetohydrodynamical dynamo is driven by cosmic rays (CR), which are continuously supplied to the disk by supernova (SN) remnants. Additionally, weak, dipolar and randomly oriented magnetic field is injected to the galactic disk during SN explosions. To compare our results directly with the observed properties of galaxies we construct realistic maps of high-frequency polarized radio emission. The main result is that CR driven dynamo can amplify weak magnetic fields up to few μG within few Gyr in barred and ringed galaxies. What is more, the modelled magnetic field configuration resembles maps of the polarized intensity observed in barred and ringed galaxies.

scholarly journals Magnetic field evolution in dwarf and Magellanic-type galaxies

2018 ◽  
Vol 611 ◽  
pp. A7 ◽  
Author(s):  
H. Siejkowski ◽  
M. Soida ◽  
K. T. Chyży
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Large Scale ◽  
Magnetic Energy ◽  
Galactic Disk ◽  
Cosmic Ray ◽  
Dark Matter Halo ◽  
Field Evolution ◽  
Low Mass ◽  
The Magnetic Field

Aims. Low-mass galaxies radio observations show in many cases surprisingly high levels of magnetic field. The mass and kinematics of such objects do not favour the development of effective large-scale dynamo action. We attempted to check if the cosmic-ray-driven dynamo can be responsible for measured magnetization in this class of poorly investigated objects. We investigated how starburst events on the whole, as well as when part of the galactic disk, influence the magnetic field evolution. Methods. We created a model of a dwarf/Magellanic-type galaxy described by gravitational potential constituted from two components: the stars and the dark-matter halo. The model is evolved by solving a three-dimensional (3D) magnetohydrodynamic equation with an additional cosmic-ray component, which is approximated as a fluid. The turbulence is generated in the system via supernova explosions manifested by the injection of cosmic-rays. Results. The cosmic-ray-driven dynamo works efficiently enough to amplify the magnetic field even in low-mass dwarf/Magellanic-type galaxies. The e-folding times of magnetic energy growth are 0.50 and 0.25 Gyr for the slow (50 km s−1) and fast (100 km s−1) rotators, respectively. The amplification is being suppressed as the system reaches the equipartition level between kinetic, magnetic, and cosmic-ray energies. An episode of star formation burst amplifies the magnetic field but only for a short time while increased star formation activity holds. We find that a substantial amount of gas is expelled from the galactic disk, and that the starburst events increase the efficiency of this process.

The Accuracy of Radiocarbon Dates

Antiquity ◽  
1963 ◽  
Vol 37 (147) ◽  
pp. 213-219 ◽  
Author(s):  
W. F. Libby
Keyword(s):  
Magnetic Field ◽  
Solar System ◽  
Cosmic Ray ◽  
Average Life ◽  
Radiocarbon Dates ◽  
Cosmic Ray Intensity ◽  
Rapid Mixing ◽  
The Past ◽  
The Earth ◽  
The Magnetic Field

The first test of the accuracy of dates obtained by the radiocarbon technique was made by determining whether dates so obtained agreed with the historical dates for materials of known age (n. 1). The validity of the radiocarbon method continues to be an important question, especially in the light of the numerous results that have been accumulated and the greater precision of the technique during the past few years (n. 2).The radiocarbon content of the biosphere depends on three supposedly independent geophysical quantities: (i) the average cosmic ray intensity over a period of 8000 years (the average life of radiocarbon) as measured in our solar system but outside the earth's magnetic field (n. 1); (ii) the magnitude (but not the orientation, because of the relatively rapid mixing over the earth's surface) of the magnetic field in the vicinity of the earth, averaged over the same period (n. 1,3); and (iii) the degree of mixing of the oceans during the same period (n. 1). The question of the accuracy of radiocarbon dates therefore is of interest to geophysicists in general as well as to the archaeologists, geologists and historians who use the dates.Previous workers in this area (n. 1, 2) have reported some discrepancies, and it is the purpose here to consider the matter further.

scholarly journals 8.14. Magnetic fields in star-forming regions of our Galaxy

1998 ◽  
Vol 184 ◽  
pp. 371-372
Author(s):  
B. Hutawarakorn ◽  
R. J. Cohen
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Zeeman Splitting ◽  
Theoretical Work ◽  
Field Configuration ◽  
Galactic Magnetic Field ◽  
Star Forming ◽  
Star Forming Regions ◽  
The Magnetic Field

Masers provide a direct way of measuring magnetic fields in star-forming regions. OH ground-state masers at 18 cm wavelength exhibit strong circular polarization due to Zeeman splitting. The implied magnetic field strength is typically a few mG, which is sufficient for the field to be dynamically important, e.g. in channelling the observed bipolar outflows. Moreover there are indications that magnetic fields in maser regions are aligned with the large-scale Galactic magnetic field (Reid & Silverstein 1990), and that bipolar molecular outflows are also aligned with the local Galactic magnetic field (Cohen, Rowland & Blair 1984). Some theoretical work in fact suggests that the magnetic field is intimately connected with the origin of the molecular outflow (e.g. Pudritz & Norman 1983; Uchida & Shibata 1985). It is therefore important to investigate the magnetic field configuration in these regions in as much detail as possible.

scholarly journals 8.1. Magnetic phenomena in galactic nuclei

1998 ◽  
Vol 184 ◽  
pp. 331-340 ◽  
Author(s):  
Mark Morris
Keyword(s):  
Magnetic Field ◽  
Galactic Center ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Galactic Nuclei ◽  
Relativistic Electrons ◽  
Predominant Orientation ◽  
The Right ◽  
The Magnetic Field ◽  
Intercloud Medium

The magnetic environment of the Galactic nucleus contrasts sharply with that of the Galactic disk. The inner few hundred parsecs of our Galaxy appear to be dominated by a strong (~milligauss) and uniform dipole field which dominates the pressure within the central intercloud medium. An attractive hypothesis for the origin of the central vertical field is that it results from the concentration of protogalactic field by radial inflow of gas throughout the Galaxy's lifetime. The predominant orientation of the magnetic field within dense molecular clouds is parallel to the galactic plane, which can be understood in terms of the strong tidal shear to which these clouds are subjected. The contrasting geometries of the cloud and intercloud fields allow for magnetic field line reconnection at cloud surfaces, which, under the right circumstances, could produce the relativistic electrons which delineate the nonthermal radio filaments near the Galactic center with their synchrotron emission. The characteristics of the Galactic center “magnetosphere” should be generalizable to all gas-rich spiral galaxies. Inadequate spatial resolution currently prevents us from exploring magnetic fields in other galactic nuclei to the same depth as in the Galactic center, but existing evidence is consistent with similar magnetic geometries elsewhere.

scholarly journals A novel analytical model of the magnetic field configuration in the Galactic center

2020 ◽  
Vol 644 ◽  
pp. A71
Author(s):  
M. Guenduez ◽  
J. Becker Tjus ◽  
K. Ferrière ◽  
R.-J. Dettmar
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Field Model ◽  
Galactic Center ◽  
Cosmic Ray ◽  
Field Structure ◽  
Magnetic Field Structure ◽  
Center Region ◽  
Magnetic Field Model ◽  
The Magnetic Field

Context. Cosmic-ray propagation is strongly dependent on the large-scale configuration of the Galactic magnetic field. In particular, the Galactic center region provides highly interesting cosmic-ray data from gamma-ray maps and it is clear that a large fraction of the cosmic rays detected at Earth originate in this region of the Galaxy. Yet because of confusion from line-of-sight integration, the magnetic field structure in the Galactic center is not well known and no large-scale magnetic field model exists at present. Aims. In this paper, we develop a magnetic field model, derived from observational data on the diffuse gas, nonthermal radio filaments, and molecular clouds. Methods. We derive an analytical description of the magnetic field structure in the central molecular zone by combining observational data with the theoretical modeling of the basic properties of magnetic fields. Results. We provide a first description of the large-scale magnetic field in the Galactic center region. We present first test simulations of cosmic-ray propagation and the impact of the magnetic field structure on the cosmic-ray distribution in the three dimensions. Conclusions. Our magnetic field model is able to describe the main features of polarization maps; it is particularly important to note that they are significantly better than standard global Galactic magnetic field models. It can also be used to model cosmic-ray propagation in the Galactic center region more accurately.

Observing the galactic magnetic field

1967 ◽  
Vol 31 ◽  
pp. 375-380
Author(s):  
H. C. van de Hulst
Keyword(s):  
Magnetic Field ◽  
Fair Agreement ◽  
Solar Neighbourhood ◽  
Galactic Magnetic Field ◽  
The Magnetic Field

Various methods of observing the galactic magnetic field are reviewed, and their results summarized. There is fair agreement about the direction of the magnetic field in the solar neighbourhood:l= 50° to 80°; the strength of the field in the disk is of the order of 10-5gauss.

Structure in the radiation of the galactic disk

1967 ◽  
Vol 31 ◽  
pp. 355-356
Author(s):  
R. D. Davies
Keyword(s):  
Magnetic Field ◽  
Galactic Disk ◽  
Galactic Magnetic Field ◽  
Measured Polarization

Observations at various frequencies between 136 and 1400 MHz indicate a considerable amount of structure in the galactic disk. This result appears consistent both with measured polarization percentages and with considerations of the strength of the galactic magnetic field.

scholarly journals The Origin and Dynamical Effects of the Magnetic Fields and Cosmic Rays in the Disk of the Galaxy

1970 ◽  
Vol 39 ◽  
pp. 168-183
Author(s):  
E. N. Parker
Keyword(s):  
Magnetic Field ◽  
Cosmic Rays ◽  
Magnetic Fields ◽  
Dynamical Behavior ◽  
Cosmic Ray ◽  
Interested Reader ◽  
Written Text ◽  
The Galaxy ◽  
Basic Ideas ◽  
The Magnetic Field

The topic of this presentation is the origin and dynamical behavior of the magnetic field and cosmic-ray gas in the disk of the Galaxy. In the space available I can do no more than mention the ideas that have been developed, with but little explanation and discussion. To make up for this inadequacy I have tried to give a complete list of references in the written text, so that the interested reader can pursue the points in depth (in particular see the review articles Parker, 1968a, 1969a, 1970). My purpose here is twofold, to outline for you the calculations and ideas that have developed thus far, and to indicate the uncertainties that remain. The basic ideas are sound, I think, but, when we come to the details, there are so many theoretical alternatives that need yet to be explored and so much that is not yet made clear by observations.

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