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Crab, spiral galaxy caught in UV light.

When the Astro Observatory spent nine days in space last December, only one of its instruments -- an ultraviolet imaging telescope -- carried camera and film. The telescope photographed more than 900 objects, including many never before imaged in the ultraviolet (SN: 1/26/91, p. 52). Now, scientists have released a second set of Astro photos, shedding light on structures both within our galaxy and far beyond.

Astro's portrait of the Crab nebula (left), a famed supernova remnant in the Milky Way, depicts the ultraviolet glow produced as electrons rush out from the spinning neutron star at the nebula's center. Intense magnetic fields surrounding the star force the charged particles to move in spiral paths and radiate ultraviolet light. In this false-color, near-ultraviolet image, blue represents the lowest intensity and the white at the nebula's center highlights the region of highest intensity.

However, comparing this image with one taken in the far-ultraviolet (not shown) reveals that the hottest, highest-energy regions do not lie at the center, reports Robert W. O'Connell of the University of Virginia at Charlottesville. He and other Astro scientists believe the energy unleashed as the high-speed electrons smash into a dense shell of and gas surrounding the neutron star may explain the hotspot's slightly off-center location.

A third Astro image (right) reveals new details about star formation within the spiral galaxy M74, about 55 million light-years from Earth. The white spots surrounding the nucleus signify regions of starbirth in the spiral arms. Scientists had already identified this starbirth pattern in ground-based, visible-light observations. But the ultraviolet photo illuminates a feature never before clearly pictured: several disruptions in M74's spiral arms that may hint at how the arms formed.

O'Connell and other Astro investigators presented the three photos at last week's American Astronomical Society meeting in Seattle.
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Title Annotation:ultraviolet images of the Crab nebula and a galaxy
Publication:Science News
Date:Jun 8, 1991
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