The strength of galactic magnetic fields
Article Abstract:
A study of the origin of galactic magnetic fields is reported. The magnitude of galactic magnetic fields had been estimated in other studies from the radio synchrotron emission arising from the accelaration of cosmic-ray electrons in the magnetic field, with the assumption that energy density in the magnetic field is equal to that in the cosmic-ray protons. The magnetic fields in irregular galaxies were estimated without making the energy equipartition assumption. The results suggest that galactic magnetic fields are too strong to have arisen from dynamo action alone. Instead, it was suggested that galactic magnetic fields arise from recent star formation.
Publication Name: Nature
Subject: Zoology and wildlife conservation
ISSN: 0028-0836
Year: 1993
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Dust particle impacts during the Giotto encounter with comet Grigg-Skjellerup
Article Abstract:
The results of the European Space Agency's Giotto Dust Impact Detection System are reported. The Giotto spacecraft came within 200 km of the nucleus of the comet Grigg-Skjellerup. Its front shield registered impacts from three meteoroid with sizes of 100, 2 and 20 micro-grams, indicating that large particles predominate in the cometary dust. The data is consistent with that from a 1986 encounter with the comet Halley, indicating a higher rate of mass loss, and thus a higher dust-to-gas ratio, from the nucleus of comets.
Publication Name: Nature
Subject: Zoology and wildlife conservation
ISSN: 0028-0836
Year: 1993
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High-energy cosmic-ray origin
Article Abstract:
The hypothesis that high-energy cosmic rays or particles result from a stochastic Fermi-type acceleration within the Milky Way Galaxy fails to provide physical values for the Galaxy's parameters at high enough energies. Moreover, incorporating the bias for head-on versus overtaking collisions turns the hypothesis into the one-dimensional restatement of a familiar result. However, the rebuttal view is that an improved version of the hypothesis based on analysis of the astrophysical data will satisfy these objections.
Publication Name: Nature
Subject: Zoology and wildlife conservation
ISSN: 0028-0836
Year: 1992
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