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Ringing up another light echo.

Ringing up another light echo

Although supernova 1987A, located in the Large Magellanic Cloud about 160,000 light-years from Earth, has been fading since the spring of 1987, astronomers are still seeing traces of light from its brightest period. That light reaches the Earth after reflecting off interstellar dust, taking a somewhat longer time to complete its journey than visible light coming directly from the supernova. Such a feature is known as a light echo.

Last year, astronomers reported observing two glowing light-echo rings approximately centered on the supernova (SN: 6/18/88, p.388). Now, Howard E. Bond and his colleagues at the Space Telescope Science Institute in Baltimore report discovery of a third ring inside the other two.

Whereas the previously discovered rings appear to correspond to two separate sheets of dust about 1,000 light-years and 400 light-years in front of the supernova as seen from the Earth, the newly observed ring suggests the presence of dust lying only 20 light-years from the supernova. Because there was no sign of the third ring in earlier observations, the researchers, conclude there is apparently a cavity or bubble in the material surrounding the supernova, at least in the direction of the Earth.

Other astronomers have already confirmed the presence of this new light-echo feature and continue to monitor changes in the other two rings. Because the echoes have retained their near-circular shapes, astronomers suspect the interstellar dust must be highly concentrated into two layers. Furthermore, the very small deviations from a circular form impose tight constraints on the curvature and inclination of these dust sheets.
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Title Annotation:supernova 1987A
Publication:Science News
Date:Mar 11, 1989
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