Direct measurement of the optical depth in a spiral galaxy
Article Abstract:
The correlation of optical extinction with light emission in spiral galaxies probably explains why spiral galaxies sometimes appear to be both opaque and transparent. This result was obtained by determining the degree of optical extinction observed in pairs of galaxies in which the nearer galaxy is illuminated from behind by the farther galaxy. The large degree of light extinction detected in many cases probably derived from the spiral structures that generate most of the light.
Publication Name: Nature
Subject: Zoology and wildlife conservation
ISSN: 0028-0836
Year: 1992
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More whirls in the whirlpool
Article Abstract:
High-resolution photos in near-infrared wavelengths reveal inner spiral arms of unprecedented length and continuity in galaxy M51. The so-called Whirlpool galaxy is already famed for its grand-design structure and clarity, but new pictures show the arms making three complete revolutions. This is incompatible with current theory, and indicates that the evolution of density-wave spiral galaxies may be influenced by unknown forces or interactions among known forces.
Publication Name: Nature
Subject: Zoology and wildlife conservation
ISSN: 0028-0836
Year: 1993
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Inner spiral structure of the galaxy M51
Article Abstract:
K-band images of spiral galaxy M51 show its spiral arms extending through three continuous revolutions, twice as far as optical images show. They reach to an angular distance of 10'', rather than the visible 30'' from the center. The extent of this inner spiral structure is inconsistent with current theory, and may be due to tidal torque from a neighboring galaxy, interaction with M51's own central bar or distortions from density waves.
Publication Name: Nature
Subject: Zoology and wildlife conservation
ISSN: 0028-0836
Year: 1993
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